Papers for Wednesday, Oct 01 2025

The ``Tensions in Cosmology'' series of conferences has been established as one of the main venues where the cosmological community collectively assesses the cracks in the concordance model and explores possible theoretical and observational remedies. The 2025 edition, held once again in Corfu, Greece, came at a crucial time: the Hubble constant $H_0$ discrepancy has now exceeded $6\sigma$, and new high-precision data from DESI, JWST, ACT, and other facilities have made this tension more robust while opening new windows on the early and late Universe. The $S_8$ tension, though milder and survey-dependent, remains an important probe of late-time structure formation, while emerging anomalies involving dynamical dark energy and neutrino physics are gaining increasing attention as potential signs of physics beyond $\Lambda$CDM. Here we provide a report on the meeting and an update on the state of the tensions in 2025, highlighting progress since the pioneering 2022 event.

For decades, the theoretical understanding of planetary nebulae (PNe) has remained in tension with the observed universal bright-end cutoff of the PN luminosity function (PNLF). While the brightest younger PN populations are expected to be brighter in their [OIII] emission than observed, recent studies have proposed circumnebular extinction to be a key ingredient for bringing their brightness down to the observed bright end. In this work we use the recently introduced PICS (PNe In Cosmological Simulations) framework to investigate the impact of different circumnebular extinction treatments on the modeled PNe and their PNLF for a large range of stellar ages and metallicities. We test how different slopes in the observed relation of extinction versus central star mass modify the bright-end cutoffs of the PNLF, finding that steeper slopes lead to large changes for young stellar populations. In contrast, the differences for older PNe are much smaller. However, for individual PNe, the extinctions observed in nearby galaxies appear to be much higher than the models predict, showing that improvements on both the modeling and observational sides are needed to gain a better understanding of the brightest and strongly extincted PNe. These findings further advance the theoretical foundation for interpreting observed extragalactic PN populations coming from more complex composite stellar populations in the future.

Stellar shells and streams are remnants of satellite galaxies visible around galaxies. Advances in low-surface-brightness observations and increasing resolution of cosmological simulations now allow investigating the properties and origin of these features. The metallicity, age, and velocity dispersion of shells and streams are investigated to infer their progenitor galaxies properties. We employed the hydrodynamical cosmological simulations Magneticum Pathfinder to extract these properties and identify the progenitors of the shells and streams. We compared to observational results from surveys and individual galaxies, matching and testing the methodology used in observations. Mock observations of shells and streams agree well with observational data regarding their morphology and spatial distribution. We find that both types of features are associated with localized depressions in stellar velocity dispersion compared to the surrounding regions. They are not as clearly distinct in metallicity and ages, though overall shells and more metal rich and streams are younger. We confirm results from idealized models that shells form commonly from radial major mergers but also through minor mergers, while streams usually form from minor mergers on circular orbits. We do not find the widths of streams to correlate with the half-mass radii of their progenitors, but the progenitors follow the mass-metallicity relation. On average, the masses measured for shells and streams approximately corresponds to 20% of the progenitor mass. We introduce a class of star-forming streams, which originate from in-situ star formation rather than the disruption of a satellite galaxy. Measuring stellar population properties of shells and streams provides the means to reconstruct the progenitor properties, and especially distinguish those streams that are not made through the disruption of a galaxy but formed in-situ.

We present the implementation and testing of a subgrid non-explosive pre-supernova (NEPS) feedback module for the COLIBRE model of galaxy formation. The NEPS module incorporates three key physical processes sourced by young, massive stars that act immediately following star formation: momentum injection from stellar winds and radiation pressure, and thermal energy from photoheating in HII regions. The age- and metallicity-dependent energy and momentum budgets are derived from BPASS stellar population models and are coupled self-consistently to the local gas properties. We test the model using a suite of smoothed particle hydrodynamics simulations of isolated, unstable gaseous disks at various numerical resolutions (gas particle masses in the range $10^4-10^6$ $\rm M_{\odot}$). We find that the NEPS module successfully regulates star formation by providing pressure support that prevents catastrophic gas collapse. This regulation improves the numerical convergence of star formation rates and disk structure. In our model, feedback from HII regions is the dominant regulatory mechanism. Furthermore, we demonstrate a crucial synergy with subsequent supernova feedback; NEPS feedback pre-processes the interstellar medium, creating a more homogeneous environment that moderates the effect of explosive feedback from supernova events. Our NEPS module thus provides a physically motivated and numerically robust framework that mitigates resolution-dependent artefacts and promotes self-regulated galaxy growth.

Giant low-surface-brightness disk galaxies (gLSBGs) are rare objects with disk radii up-to 160 kpc and dynamical masses of an order of up to 10$^{12}$ $M_{\odot}$. Their very existence challenges currently accepted theories of galaxy formation and evolution, as it is difficult to build such large, dynamically cold disks through mergers without destroying them. We present deep MUSE mosaic observations of two nearby gLSBGs with compact elliptical satellites: UGC 1382, which hosts a globally counter-rotating gaseous disk, and AGC 192040, which does not. We analyze properties of ionized gas and present spatially resolved kinematics and metallicity maps; as well as stellar population analysis for the central regions of the galaxies. The radial gradients of gas-phase metallicities are flat for both galaxies. Our estimates of the effective oxygen yield suggest 'passive' gas in the outskirts of both stellar systems that is not involved in star formation. Our observational data indicate that both galaxies experienced mergers several Gyrs ago. However, the scenarios of formation of giant disks appear to be slightly different for these two systems. For AGC 192040 we propose the gas accretion from the filament followed by the intermediate-mass ratio merger with the companion on a prograde orbit. For UGC 1382 multiple gas-rich mergers with companions on retrograde orbits are preferred by the data.

A physical understanding of galaxy formation and evolution benefits from an understanding of the connections between galaxies, their host dark matter halos, and their environments. In particular, interactions with more-massive neighbors can leave lasting imprints on both galaxies and their hosts. Distinguishing between populations of galaxies with differing environments and interaction histories is therefore essential for isolating the role of environment in shaping galaxy properties. We present a novel neural-network based method, which takes advantage of observable measures of a galaxy and its environment to recover whether it (1) is a central or a satellite, (2) has experienced an interaction with a more massive neighbor, and (3) is currently orbiting or infalling onto such a neighbor. We find that projected distances to, redshift separations of, and relative stellar masses with respect to a galaxy's 25 nearest neighbors are sufficient to distinguish central from satellite halos in $> 90\%$ of cases, with projection effects accounting for most classification errors. Our method also achieves high accuracy in recovering interaction history and orbital status, though the network struggles to distinguish between splashback and infalling systems in some cases due to the lack of velocity information. With careful treatment of the uncertainties introduced by projection and other observational limitations, this method offers a new avenue for studying the role of environment in galaxy formation and evolution.

Shock fronts driven by active galactic nuclei in galaxy cluster cores represent a promising mechanism to heat the intracluster gas by converting kinetic energy into thermal energy through gas compression, thereby offsetting radiative cooling. Despite their potential importance, such shocks are challenging to detect, requiring deep X-ray exposures, and have only been identified in ten clusters. We present the first systematic detection and characterization of AGN-driven shocks in simulated clusters from the TNG-Cluster magnetohydrodynamic cosmological zoom-in simulations of galaxies. TNG-Cluster exhibits a rich variety of X-ray structures, including realistic populations of X-ray cavities, as well as shocks, produced by its AGN feedback model, without collimated, relativistic jets, nor cosmic rays. We produce mock Chandra observations with deep exposure times, for a sample of 100 clusters, mass-matched (M$_{500c}=1.2$ - $8.5 \times 10^{14}$ M$_\odot$) to the ten observed clusters with shocks. Using observational techniques, we identify shocks through surface brightness edges fitted with broken power laws and associated density and temperature jumps. We detect 50 shocks in 30 of the 100 clusters, with ~35% hosting multiple shocks. These shocks lie within a hundred kiloparsec of the central SMBH, are weak (Mach number < 2, median ~ 1.1), and are associated with cavities in about half of the cases. Both in observations and in TNG-Cluster, shocks tend to be located at larger radii than cavities, with median offsets of 46 and 27 kpc, respectively. The observationally inferred shock powers are comparable to the cluster cooling luminosities (10$^{44-46}$ erg s$^{-1}$), suggesting that shocks in the simulation are crucial heating mechanisms. Our results indicate that shocks play a role as important as cavities in balancing cooling in cluster cores, acting isotropically and up to larger distances.

In the past decade, Swift has performed several AGN high-cadence reverberation mapping campaigns, and generally found that the UV/optical interband lags are $\sim$3 times longer than predicted for a standard thin disk, thus coined "the accretion disk size problem". Here we present a systematic sample of Swift-monitored AGN. In this analysis, we confirm the accretion disk size problem, but find that the lag excess occurs only in the subset of obscured AGN, which show a significantly elevated mean normalization of $5.21 \pm 0.47$ ($p = 0.008$), whereas the unobscured AGN exhibit a mean excess consistent with standard disk predictions ($1.00 \pm 0.31$). Correlation and regression analyses similarly reveal X-ray column density as the strongest predictor of lag excess, explaining over 80% of its variance. We interpret these results as line-of-sight obscuration being linked to the too-long lags via additional reprocessed emission from the absorbing material itself. The consistency of lags in the unobscured subgroup with standard disk predictions suggests that the accretion disk size problem is not the result of shortcomings of standard accretion disk theory nor contamination by the broad-line region (BLR). X-ray to UV lag amplitudes and correlations show more complex and variable behavior in obscured AGN, suggesting that obscuration may disrupt or complicate the connection between high- and low-energy emission potentially through reprocessing, scattering, and/or ionization changes.

The hot gas in the outskirts of galaxy cluster-sized halos, extending around and beyond the virial radius into nearby accretion regions, remains among one of the least explored baryon components of large-scale cosmic structure. We present a stacking analysis of 680 galaxy clusters located in the western Galactic hemisphere, using data from the first two years of the SRG/eROSITA All-Sky Survey. The stacked X-ray surface brightness profile reveals a statistically significant signal extending out to 2r200m (~4.5 Mpc). The best-fit surface brightness profile is well described by a combination of terms describing orbiting and infalling gas, with a transition occurring around r200m. At this radius, the best-fit gas density is 2.5e-5 cm^-3, corresponding to a baryon overdensity of 30. By integrating the gas density profile out to r200m, we infer a gas fraction of 90% of the universal baryon fraction with the assumption of a typical halo concentration, indicating the completeness of the baryon budget within large radii. Additionally, we examine the hot gas distribution in massive clusters in the IllustrisTNG simulations from the halo center to the accretion region. This analysis reveals differences in radial gas profiles depending on whether the direction probes voids or nearby cosmic filaments. Beyond r200m, the density profile along the filament direction exceeds that along the void direction. This pattern aligns with the observed transition radius between the one-halo and two-halo terms, suggesting that r200m is the approximate radius marking the location at which cosmic filaments connect to galaxy clusters. Meanwhile, the comparisons of the gas density profile and gas fraction profile between the observation and the IllustrisTNG simulation suggest that the feedback processes in the stacking sample are more efficient than the IllustrisTNG model in distributing gas to large radii.

Cross-correlations techniques offer an alternative method to search for molecular species in JWST observations of exoplanet atmospheres. In a previous article, we applied cross-correlation functions for the first time to JWST NIRSpec/G395H observations of exoplanet atmospheres, resulting in a detection of CO in the transmission spectrum of WASP-39b and a tentative detection of CO isotopologues. Here we present an improved version of our cross-correlation technique and an investigation into how efficient the technique is when searching for other molecules in JWST NIRSpec/G395H data. Our search results in the detection of more molecules via cross-correlations in the atmosphere of WASP-39b, including $\rm H_{2}O$ and $\rm CO_{2}$, and confirms the CO detection. This result proves that cross-correlations are a robust and computationally cheap alternative method to search for molecular species in transmission spectra observed with JWST. We also searched for other molecules ($\rm CH_{4}$, $\rm NH_{3}$, $\rm SO_{2}$, $\rm N_{2}O$, $\rm H_{2}S$, $\rm PH_{3}$, $\rm O_{3}$ and $\rm C_{2}H_{2}$) that were not detected, for which we provide the definition of their cross-correlation baselines for future searches of those molecules in other targets. We find that that the cross-correlation search of each molecule is more efficient over limited wavelength regions of the spectrum, where the signal for that molecule dominates over other molecules, than over broad wavelength ranges. In general we also find that Gaussian normalization is the most efficient normalization mode for the generation of the molecular templates.

Red giants undergo the first dredge-up, a mixing event that creates a connection between their surface [C/N] and their mass and age. We derive a [C/N]-Age relationship for red giants calibrated on APOGEE DR17 abundances and APOKASC-3 asteroseismic ages. We find that we can use [C/N] to reliably recover asteroseismic ages between 1 and 10 Gyr with average uncertainties of 1.64 Gyr. We find that [C/N] yields concordant ages, with modest offsets, for stars in different evolutionary states. We also find that the [C/N]-birth mass relationship is robust for luminous giants, and argue that this is an advantage over direct asteroseismology for these stars. We use our ages to infer Galactic birth abundance trends in [Fe/H] and [Mg/H] as a function of position in the Galactic disk. We filter out stars with kinematic or chemical properties consistent with migrators and found the number of migrators to be much lower than expected by standard radial migration prescriptions. The remaining population shows weak chemical evolution trends, on the order of 0.01 dex/Gyr, over the last 10 Gyr across a wide range of radii.

Today's most detailed characterization of exoplanet atmospheres is accessible via transit spectroscopy (TS). Detecting transiting exoplanets only yields their size, and it is thus standard to measure a planet's mass before moving towards their atmospheric characterization, or even the publication of their discovery. This framework, however, can act as a bottleneck for high-throughput exoplanetology. Here, we review existing applications of an alternative approach deriving exoplanet masses in small JWST atmospheric exploration programs and quantify the potential of its systematic application. We find that for $\sim$20\% of transiting exoplanets with existing mass constraints, a small JWST exploration program could yield the planetary mass with a similar--or better -- precision. Such results suggest that proceeding directly with atmospheric exploration programs for favorable exoplanets (i.e., with a transmission spectroscopy metric, TSM, $\geq$100) could substantially reduce the time from detection to exoplanet atmospheric study and further support JWST's scientific output over its lifetime while saving up to 20\% of resources on radial-velocity (RV) facilities. Furthermore, it can substantially increase the sample of characterized planets of three distinct subpopulations (Neptune-sized, young, and hot-star exoplanets), each providing specific insights into formation and evolution processes. As the field of exoplanets increasingly turns to directly imaged planets, mastering the determination of planetary masses from atmospheric spectra will become essential.

The accretion flow in AGN is not well understood, motivating intensive monitoring campaigns of multiwavelength variability to probe its structure. One of the best of these is the 3 year optical/UV/X-ray approximately daily monitoring campaign on Fairall\,9, a fairly typical moderate accretion rate AGN. The UV lightcurve shows a clear increase over $\sim 50$ days between years 1 and 2, strongly coherent with the X-ray lightcurve rise. This changes the average spectral energy distribution such that the disc component is stronger while the X-ray spectrum steepens, so that the total X-ray power remains roughly constant. Outside of this global change, we apply a Fourier resolved analysis to test stochastic models where intrinsic fluctuations in the UV disc propagate down into the hard X-ray emission region via both changing the seed photon flux for Compton scattering (short light travel timescale) and changing the electron density (longer propagation timescale). Unlike these models, the hard X-rays are not particularly well correlated with the UV, and also have the wrong sign in that the hard X-rays marginally lead the UV fluctuations. We show that this is instead consistent with uncorrelated stochastic fluctuations in both the UV (slow) and X-ray (fast), which are linked together only weakly via light travel time. These variability properties, as well as the changes in the SED, has implications for our understanding of AGN structure and physics, as well as future monitoring campaigns.

Cosmic voids are key elements in our understanding of the large-scale structure of the Universe. They are crucial to constrain cosmological parameters, understand the structure formation and evolution of our Universe, and they could also be pristine laboratories for studying galaxy formation without all the hassle due to environmental effects. Thus, the ability to accurately and consistently identify voids, both in numerical simulations and in observations, becomes mandatory. We present Algorithm for Void Identification in coSMology (AVISM), a new void finder for analysing both cosmological simulation outputs and observational galaxy catalogues. In the first case, the code should handle raw particle or cell data, dark matter halos or synthetic galaxy catalogues. In the case of observational data, the code should be coupled with external tools providing with the required dynamical information to apply the algorithm. A set of numerical tests designed to assess the code's capabilities are carried out. AVISM's performance is also compared, both statistically and on a one-to-one basis, with the DIVE and ZOBOV state-of-the-art void finders using as input a dark matter halo catalogue from a large-volume cosmological simulation. An application to a galaxy survey is provided to demonstrate the code's ability to handle real data. We have designed a new void finder algorithm that combines geometrical and dynamical information to identify void regions plus a hierarchical merging process to reconstruct the whole 3D structure of the void. The outcome of this process is a void catalogue with complex boundaries without assuming a prior shape. This process can be repeated at different levels of resolution using finer grids, leading to a list of voids-in-voids and a proper description of void substructure.

Stellar multiplicity plays a crucial role in shaping planet formation and dynamical evolution. We present a survey of 54 TESS Objects of Interest (TOIs) within 300 pc that exhibit significant Hipparcos-Gaia astrometric accelerations. We identified 35 TOIs with stellar companions at projected separations between $0.1^{\prime\prime}$ to $2^{\prime\prime}$ (or $10-200$ AU). We also identified 12 TOIs that could host planetary-mass or brown dwarf companions, including 6 that are newly discovered. Furthermore, we perform three-dimensional orbital characterization for 12 binaries hosting confirmed planets or planet candidates, allowing us to constrain the line-of-sight mutual inclination, $\Delta I_{\mathrm{los}}$, between the planetary and binary orbits. Combining our sample with previous measurements, we apply Bayesian hierarchical analysis to a total of 26 binary systems with S-type transiting planets ($r_p<5R_{\oplus}$). Specifically, we fit the $\Delta I_{\mathrm{los}}$ distribution with both single (Rayleigh) and mixture models (two-component Rayleigh and Rayleigh-isotropic mixture). We find the mixture models are strongly favored ($\log Z\gtrsim13.9$, or $\approx$5$\sigma$), indicating the observed planet-binary $\Delta I_{\mathrm{los}}$ values likely originate from two underlying populations: one nearly aligned ($\sigma_1 = 2^{\circ}.4^{+0.7}_{-0.9}$) and one with more scattered mutual inclinations ($\sigma_2 = 23^{\circ}.6^{+8.8}_{-7.1}$). Alternatively, the misaligned systems can be equally well described by an isotropic distribution of inclinations. This observed dichotomy likely reflects different dynamical histories. Notably, the misaligned population only emerges in systems with stellar periastron distances $>40$ AU while systems with close-in or eccentric stellar companions (periastron distances $<40$ AU) preserve planet-binary alignment.

We investigate how Milky Way-like environments influence the sizes and structural properties of low-mass galaxies by comparing satellites of Milky Way analogs from the Satellites Around Galactic Analogs (SAGA) Survey with two control samples: an environmentally agnostic population from the SAGA background (SAGAbg) sample and isolated galaxies from the SDSS NASA-Sloan Atlas. All sizes and structural parameters are measured uniformly using pysersic to ensure consistency across samples. We find the half-light sizes of SAGA satellites are systematically larger than those of isolated galaxies, with the magnitude of the offset ranging from 0.05 to 0.12 dex (10-24%) depending on the comparison sample and completeness cuts. This corresponds to physical size differences between 85-200 pc at 10^7.5 solar masses and 220-960 pc at 10^10 solar masses. This offset persists among star-forming galaxies, suggesting that environment can influence the structure of low-mass galaxies even before it impacts quenching. The intrinsic scatter in the size-mass relation is lower for SAGA satellites than isolated galaxies, and the Sérsic index distributions of satellites and isolated galaxies are similar. In comparison to star-forming satellites, quenched SAGA satellites have a slightly shallower size-mass relation and rounder morphologies at low-mass, suggesting that quenching is accompanied by structural transformation and that the processes responsible differ between low- and high-mass satellites. Our results show that environmental processes can imprint measurable structural differences on satellites in Milky Way-mass halos.

Early light curves of many core-collapse supernovae (SNe) are thought to be powered by the interaction of the shock wave with optically thick extended material, either a bound envelope or preexplosion ejected circumstellar matter (CSM). We analytically analyze the early emission produced by a shock with velocity $v$ traversing a material of mass $M_\mathrm{e}$ and opacity $\kappa$ extending to radius $R_\mathrm{e}$, and show the emission varies qualitatively with varying $\tau_\mathrm{e}=\kappa\!M_\mathrm{e}/(4\pi\!R_\mathrm{e}^2)$: For $\tau_\mathrm{e}\gg\!c/v$ a shock breakout occurs near $R_\mathrm{e}$ producing an ``edge breakout"- a UV-dominated breakout burst followed by ``cooling emission" of the shock-heated material; for $\tau_\mathrm{e}\lesssim\!c/v$ a ``wind breakout" occurs- the breakout pulse is prolonged and followed by extended emission shifting from UV to X-ray as the shock becomes collisionless. We derive the dependence on $\{v,\kappa,M_\mathrm{e},R_\mathrm{e}\}$ of the duration and luminosity characterizing the different emission phases, and show that current observations typically do not allow inference of all parameters. In particular, since the optical bands lie in the Rayleigh-Jeans tail of radiation emitted during the cooling phase, the observed cooling luminosity depends weakly on radius, $\propto\!R_\mathrm{e}^{1/4}$, leading to $1-2$ orders of magnitude uncertainty in its inferred value. This suggests, e.g., that the common day-scale light curve features in Stripped-Envelope SNe do not necessarily imply material extending to $R_\mathrm{e}\sim10^3\!R_\odot$ and are often consistent with low-mass $R_\mathrm{e}\sim\!10^2\!R_\odot$ bound envelopes. Early multiband coverage (especially in UV/X-ray) can break these degeneracies; the forthcoming \emph{ULTRASAT} UV mission will allow inferring the properties of extended material around the population of SNe progenitors.

We present the first VLTI/GRAVITY observations at R$_\lambda \sim 4000$ of $\beta$ Pic b. These four high S/N ($\sim$20) K-band spectra conserve both the pseudo-continuum and molecular absorption patterns. We analyze them with four self-consistent forward model grids (Exo-REM, ATMO, BT-Settl, Sonora) exploring $T_{\mathrm{eff}}$, log(g), metallicity, C/O, and $^{12}$CO/$^{13}$CO ratio. We also upgrade our forward modeling code \texttt{\textit{ForMoSA}} to account for the data multi-modality and combine the GRAVITY epochs with published 1-5 $\mu$m photometry, low- to medium-resolution spectra (0.9-7 $\mu$m), and high-resolution echelle spectra (2.1-5.2 $\mu$m). Sonora and Exo-REM are statistically preferred. Exo-REM yields $T_{\mathrm{eff}}$ $=1607.45^{+4.85}_{-6.20}$ K and log(g) $=4.46^{+0.02}_{-0.04}$ dex from GRAVITY alone, and $T_{\mathrm{eff}}$ $=1502.74^{+2.32}_{-2.14}$ K and log(g) $=4.00\pm0.01$ dex when including all datasets. Archival data significantly affect the retrieved parameters. C/O remains solar ($0.552^{+0.003}_{-0.002}$) while [M/H] reaches super-solar values (0.50$\pm$0.01). We report the first tentative constraint on log($^{12}$CO/$^{13}$CO) $\sim$1.12, though this remains inconclusive due to telluric residuals. Additionally, we estimate the luminosity to be log(L/L$_\odot$) $=-4.01^{+0.04}_{-0.05}$, implying a heavy-element content of up to $\sim$5% (20-80 M$_\oplus$) given the system age and dynamical mass measurements. Access to both continuum and molecular lines at K-band significantly impacts the metallicity, possibly owing to collision-induced absorption shaping the continuum. Echelle spectra do not dominate the final fit with respect to lower resolution data. Future multi-modal frameworks should include weighting schemes reflecting bandwidth and central wavelength coverage.

Understanding the origin of stars within a galaxy - whether formed in-situ or accreted from other galaxies (ex-situ) - is key to constraining its evolution. Spatially resolving these components provides crucial insights into a galaxy's mass assembly history. We aim to predict the spatial distribution of ex-situ stellar mass fraction in MaNGA galaxies, and to identify distinct assembly histories based on the radial gradients of these predictions in the central regions. We employ a diffusion model trained on mock MaNGA analogs (MaNGIA), derived from the TNG50 cosmological simulation. The model learns to predict the posterior distribution of resolved ex-situ stellar mass fraction maps, conditioned on stellar mass density, velocity, and velocity dispersion gradient maps. After validating the model on an unseen test set from MaNGIA, we apply it to MaNGA galaxies to infer the spatially-resolved distribution of their ex-situ stellar mass fractions - i.e. the fraction of stellar mass in each spaxel originating from mergers. We identify four broad categories of ex-situ mass distributions: flat gradient, in-situ dominated; flat gradient, ex-situ dominated; positive gradient; and negative gradient. The vast majority of MaNGA galaxies fall in the first category - flat gradients with low ex-situ fractions - confirming that in-situ star formation is the main assembly driver for low- to intermediate-mass galaxies. At high stellar masses, the ex-situ maps are more diverse, highlighting the key role of mergers in building the most massive systems. Ex-situ mass distributions correlate with morphology, star-formation activity, stellar kinematics, and environment, indicating that accretion history is a primary factor shaping massive galaxies. Finally, by tracing their assembly histories in TNG50, we link each class to distinct merger scenarios, ranging from secular evolution to merger-dominated growth.

Kinematic studies of young stars and star clusters have increased our understanding of the process of star formation and evolution in the Milky Way. FU Orionis objects are a specific class of young stellar object notable for their extremely high disk-to-star accretion rates. We use parallax and proper motion information from the Gaia astrometric survey to study five known FU Ori stars towards the Cygnus clouds, in the distance range ~500-900 parsecs, and seek evidence of their kinematic association with proximal stellar groups or clusters. We develop multiple search criteria within the Gaia datasets to look for nearby stellar aggregates and to reliably isolate their likely member stars. We show that V1057 Cygni and HBC 722 are kinematically consistent with the 3D locations as well as the inferred proper motion fields of the North America Nebula cluster. We show a similar association of V1515 Cygni with NGC 6914 in the Cygnus-X region, and of V2494 Cygni with stars in the dark cloud LDN 1003 and Braid Nebula. Further, we find that V1735 Cygni is consistent in both position and proper motion with the streamer structure of IC 5146, and we trace the streamer's similar proper motions to the main cluster. Color-magnitude diagrams of all identified clusters show the presence of pre-main-sequence populations, strengthening the likelihood of a physical association between the young FU Ori stars and their respective nearby clusters.

Exascale supercomputing unleashes the potential for simulations of astrophysical systems with unprecedented resolution. Taking full advantage of this computing power requires the development of new algorithms and numerical methods that are GPU friendly and scalable. In the context of multi-fluid dust-gas dynamics, we propose a highly accurate algorithm that is specifically designed for GPUs. We developed a multi-fluid gas-dust algorithm capable of computing friction terms on GPU architectures to machine precision, with the constraint for the drag-time step to remain a fraction of the global hydrodynamic time step for computational efficiency in practice. We present a scaling-and-squaring algorithm tailored to modern architectures for computing the exponential of the drag matrix, enabling high accuracy in friction calculations across relevant astrophysical regimes. The algorithm was validated through the Dustybox Dustywave and Dustyshock tests. The algorithm was implemented and tested in two multi-GPU codes with different architectures and GPU programming models: Dyablo, an adaptive mesh refinement code based on the Kokkos library, and Shamrock, a multi-method code based on Sycl. On current architectures, the friction computation remains acceptable for both codes (below the typical hydro time step) up to 16 species, enabling a further implementation of growth and fragmentation. This algorithm might be applied to other physical processes, such as radiative transfer or chemistry.

The delay in arrival time of the multiple images of gravitationally lensed supernovae (glSNe) can be related to the present-day expansion rate of the universe, $H_{0}$. Despite their rarity, Rubin Observatory's Legacy Survey of Space and Time (Rubin-LSST) is expected to discover tens of galaxy-scale glSNe per year, many of which will not be resolved due to their compact nature. Follow-up from ground- and space-based telescopes will be necessary to estimate time delays to sufficient precision for meaningful $H_{0}$ constraints. We present the Glimpse model (GausSN Light curve Inference of Magnifications and Phase Shifts, Extended) that estimates time delays with resolved and unresolved observations together for the first time, while simultaneously accounting for dust and microlensing effects. With this method, we explore best follow-up strategies for glSNe observed by Rubin-LSST. For unresolved systems on the dimmest end of detectability by Rubin-LSST, having peak i-band magnitudes of 22-24 mag, the time delays are measured to as low as 0.7 day uncertainty with 6-8 epochs of resolved space-based observations in each of 4-6 optical and NIR filters. For systems of similar brightness that are resolved by ground-based facilities, time delays are consistently constrained to 0.5-0.8 day precision with 6 epochs in 4 optical and NIR filters of space-based observations or 8 epochs in 4 optical filters of deep ground-based observations. This work improves on previous time-delay estimation methods and demonstrates that glSNe time delays of $\sim10-20$ days can be measured to sufficient precision for competitive $H_{0}$ estimates in the Rubin-LSST era.

The distribution of binary black hole (BBH) masses and its evolution with redshift provide key insights into the different formation channels of the compact objects and their evolution with cosmic time and stellar properties such stellar metallicity and star formation rate history. We present a non parametric, model-independent joint reconstruction of the redshift evolution of BBH mass distribution from gravitational wave (GW) catalog GWTC-4.0 from the fourth observation of LIGO-Virgo-KAGRA (LVK). This method simultaneously searches for the signature of any linear and quadratic redshift evolution with respect to the low redshift in a Bayesian framework taking into accounting the detector selection effects. We find tentative evidence for a linear redshift-dependent evolution of the mass distribution, consistent over a mass range ($m \gtrsim 50\,M_\odot$). While lower mass systems shows no signature of evolution. The quadratic term remains consistent with zero, indicating that a simple linear dependence adequately describes the population up to redshift $z \sim 1$. In future with more GW sources, this technique can shed light into the true nature of the redshift dependence and possibility to uncover subtle evolutionary features in BBH populations and to probe the cosmic history of black hole formation.

Although numerous dynamical techniques have been developed to estimate the total dark matter halo mass of the Milky Way, it remains poorly constrained, with typical systematic uncertainties of 0.3 dex. In this study, we apply a neural network-based approach that achieves high mass precision without several limitations that have affected past approaches; for example, we do not assume dynamical equilibrium, nor do we assume that neighboring galaxies are bound satellites. Additionally, this method works for a broad mass range, including for halos that differ significantly from the Milky Way. Our model relies solely on observable dynamical quantities, such as satellite orbits, distances to larger nearby halos, and the maximum circular velocity of the most massive satellite. In this paper, we measure the halo mass of the Milky Way to be $\log_{10} M_\mathrm{vir}/\Msun = 12.20^{+0.163}_{-0.138}$. Future studies in this series will extend this methodology to estimate the dark matter halo mass of M31, and develop new neural networks to infer additional halo properties including concentration, assembly history, and spin axis.

We investigate the resolved properties of star-forming clumps and their host galaxies at $0.5<z<5$ in the JWST CANUCS fields. We find that the fraction of clumpy galaxies peaks near $z\sim2$ for galaxies with masses of $\log(M_{g,*}/M_\odot)\geq10$, while galaxies with masses of $8.5 \leq \log(M_{g,*}/M_\odot) < 10$ show lower clumpy fractions with little redshift evolution. We identify and measure individual clump masses, finding that the aggregated clump stellar mass function (cSMF) follows a power-law slope of $\alpha = -2$ across all redshift bins, broadly consistent with \textit{in-situ} clump formation. However, when split by galaxy masses, the cSMF is found to be flatter ($\alpha\sim-1.6$) for massive galaxies and steeper ($\alpha\sim-2.3$) for lower mass galaxies, with little redshift evolution in both cases. We explore how different formation mechanisms and disruptive processes affect the shape of the clump mass function. In particular, we find that the cSMF slope is flatter with increasing gas fractions in younger clump populations ($<300$ Myr old), suggesting that higher gas availability leads to more massive clumps forming at the time of formation. Alternatively, many high-redshift galaxies in the sample have disturbed morphologies and simulations show that clumps of \textit{ex-situ} origins can flatten the cSMF slope. We also investigate the evolution of clump populations, where we find the cSMF slope become flatter as clumps evolve and age. We interpret this as an indication of the long-term survivability of massive clumps, with feedback mechanisms preferentially disrupting low-mass clumps. Overall, the galaxy-mass dependent cSMF and age distribution point to a complex history for clumps, involving different and competing mechanisms for their formation and destruction.

The upcoming galaxy large-scale surveys, such as the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST), will generate photometry for billions of galaxies. The interpretation of large-scale weak lensing maps, as well as the estimation of galaxy clustering, requires reliable redshifts with high precision for multi-band photometry. However, obtaining spectroscopy for billions of galaxies is impractical and complex; therefore, having a sufficiently large number of galaxies with spectroscopic observations to train supervised algorithms for accurate redshift estimation is a significant challenge and an open research area. We propose a novel methodology called Co-SOM, based on Co-training and Self-Organizing Maps (SOM), integrating labeled (sources with spectroscopic redshifts) and unlabeled (sources with photometric observations only) data during the training process, through a selection method based on map topology (connectivity structure of the SOM lattice) to leverage the limited spectroscopy available for photo-z estimation. We utilized the magnitudes and colors of Sloan Digital Sky Survey data release 18 (SDSS-DR18) to analyze and evaluate the performance, varying the proportion of labeled data and adjusting the training parameters. For training sets of 1% of labeled data ($\approx 20{,}000$ galaxies) we achieved a performance of bias $\Delta z = 0.00007 \pm 0.00022$, precision $\sigma_{zp} = 0.00063 \pm 0.00032$, and outlier fraction $f_{\mathrm{out}} = 0.02083 \pm 0.00027$. Additionally, we conducted experiments varying the volume of labeled data, and the bias remains below $10^{-3}$, regardless of the size of the spectroscopic or photometric data. These low-redshift results demonstrate the potential of semi-supervised learning to address spectroscopic limitations in future photometric surveys.

Forecasting the arrival of coronal mass ejections (CMEs) is vital for protecting satellites, power systems, and human spaceflight. We present HELIOPANDA: Heliospheric Observer for Predicting CME Arrival via Nonlinear Drag Assimilation, a framework that integrates the Drag-Based Model (DBM) with spacecraft observations using iterative parameter estimation and Kalman filter assimilation. We introduce a method for estimating the solar wind speed $w$ and drag parameter $\gamma$, two key but usually unknown quantities controlling CME propagation, through direct solutions of the DBM equations. We tested the method on 4,480 synthetic CME profiles spanning CME speeds of $200-3500$ km/s, solar wind speeds of $250-800$ km/s, and drag parameters of $0.1-1.0\times10^{-7}$ km$^{-1}$. The results demonstrate that the framework provides accurate reconstructions of the DBM input parameters, providing a solid basis for in-situ and remote-sensing applications. By testing a single virtual spacecraft positioned at nine distances along the Sun-Earth line, HELIOPANDA achieved arrival-time errors as low as 0.6 hours for a 600 km/s CME and 1 hour for a 2500 km/s CME when the spacecraft was located 30 million km from the Sun. We developed a Kalman filter framework to assimilate noisy heliospheric data into the DBM, enabling recursive updates of CME kinematics and robust estimates of $w$ and $\gamma$, and yielding Earth and Mars arrival-time predictions within $1-2$ hours using 160 simulated hourly measurements. By combining DBM, parameter recovery, and data assimilation, HELIOPANDA provides a pathway to real-time, multi-point CME forecasts, suited to observations from Solar Orbiter, Parker Solar Probe, PUNCH, and planned L4/L5 missions.

Redshifted self-absorption features in molecular lines are commonly interpreted as signatures of gravitational collapse in pre- and protostellar cores. The shape of the line profile then encodes information on the dynamics of the collapse. There exist well-established observational techniques to estimate infall velocities from these profiles, but these have historically been calibrated on constant-velocity slab models, whereas more realistic simulations of gravitational collapse produce highly non-uniform radial velocity profiles. We produce synthetic line observations of a simulated collapsing prestellar core, including a treatment of the time-dependent chemical evolution. Applying observational techniques to the synthetic line profiles, we find that the estimated infall velocities are significantly and systematically lower than the mass-weighted infall velocities from the simulation. This is primarily because the self-absorption features tend to originate from the outer regions of the core, well beyond the location of the peak infall velocity. Velocities and mass accretion rates measured via these techniques are likely to underestimate the true values.

The recent announcement of the detection of the ultra-high-energy (UHE) neutrino event KM3-230213A by the KM3NeT telescope represents a critical opportunity to explore the origins of cosmic neutrinos and their potential gamma-ray counterparts. With an inferred neutrino energy exceeding 100 PeV, this event stands as the most energetic neutrino observed to date. The large offset from the galactic plane (11 degrees) and the presence of several blazars with temporally correlated multiwavelength counterparts within the 3 degrees localization region raise the possibility of an extragalactic origin. Additionally, the event's apparent tension with IceCube constraints suggests that it could be transient in nature rather than cosmogenic. VERITAS conducted a targeted follow-up campaign to search for very-high-energy (VHE, greater than 100 GeV) gamma-ray emission associated with KM3-230213A. Observations were performed in February and March 2025, using a four-point wobble strategy centered on the best-fit neutrino position, covering nearly the entire 90 percent confidence region. These observations probe potential hadronic gamma-ray emission from a common origin with the neutrino, placing constraints on particle-acceleration scenarios. We present the results of this search, including upper limits on very-high-energy gamma-ray flux and their implications for possible source models of KM3-230213A.

Digital tracking detects faint solar system bodies by stacking many images along hypothesized orbits, revealing objects that are undetectable in every individual exposure. Previous searches have been restricted to small areas and short time baselines. We present a general framework to quantify both sensitivity and computational requirements for digital tracking of nonlinear motion across the full sky over multi-year baselines. We start from matched-filter stacking and derive how signal-to-noise ratio (SNR) degrades with trial orbit mismatch, which leads to a metric tensor on orbital parameter space. The metric defines local Euclidean coordinates in which SNR loss is isotropic, and a covariant density that specifies the exact number of trial orbits needed for a chosen SNR tolerance. We validate the approach with Zwicky Transient Facility (ZTF) data, recovering known objects in blind searches that stack thousands of images over six years along billions of trial orbits. We quantify ZTF's sensitivity to populations beyond 5 au and show that stacking reaches most of the remaining Planet 9 parameter space. The computational demands of all-sky, multi-year tracking are extreme, but we demonstrate that time segmentation and image blurring greatly reduce orbit density at modest sensitivity cost. Stacking effectively boosts medium-aperture surveys to the Rubin Observatory single-exposure depth across the northern sky. Digital tracking in dense Rubin observations of a 10 sq. deg field is tractable and could detect trans-Neptunian objects to 27th magnitude in a single night, with deep drilling fields reaching fainter still.

The surfaces of rotating stars serve as a window into their interiors, magnetic dynamos, and are important in other areas including exoplanet discovery and atmospheric characterization. While indirect techniques such as photometry and Doppler imaging have been studied for their ability to map stellar surfaces, the gold standard remains optical long-baseline interferometry. In this paper, we develop new closed-form solutions for the interferometric visibility of a rotating star with an arbitrary inhomogeneous surface. We introduce the concept of 'stellar rotation synthesis' in interferometry--an analog of Earth rotation synthesis--where stellar rotation adds information to the spherical harmonic modes representing the star's surface intensity. We implement these solutions in the open-source package harmonix, written in JAX with automatic differentiation, providing a rich ecosystem for fitting and inference. Inspired by similar studies for photometry and Doppler imaging, we use simulations of a fiducial star as observed by the CHARA Array and intensity interferometers to perform a comprehensive theoretical study of the information theory of the starspot mapping problem in interferometry. We show that adding simultaneous photometry from a space-based instrument such as TESS adds complementary spatial information to interferometry and can improve the precision on the map coefficients by over an order of magnitude, enabling the detailed mapping of nearby main-sequence stars with current facilities. Finally, we evaluate the performance of existing and proposed intensity interferometers for stellar surface mapping.

The Galactic bulge is one of the most information-dense regions to study resolved stellar populations, variables, and transients, such as microlensing events. Studies toward the Galactic bulge are complicated by the large and variable extinction along the line of sight. We measure the near-infrared $A_{K_S}$ extinction and $E(H-K_S)$ reddening in this region using $H$- and $K$-band photometry obtained with the 2017 UKIRT microlensing survey. We fit the apparent magnitude and color distribution of bright giants in the bulge to recover the apparent magnitude and color of Red Clump stars, which are known to be standard candles and crayons. We present $2^\prime \times 2^\prime$ resolution maps in UKIRT fields between $-2.15^{\circ} \le l \le 2.71^{\circ}$ and $-2.69^{\circ} \le b \le 2.03^{\circ}$ of the $A_{K_S}$ extinction and the $E(H-K_S)$ reddening. We find large variations in the $K_S$-band extinction and $E(H-K_S)$ reddening on all the scales we probe. We find that a constant, standard extinction law is a poor representation of the relationship between the extinction and reddening we measure in fields of different latitudes. These maps will be useful for understanding the near-infrared extinction law for sight lines close to the Galactic plane, as well as for final field selection for the Nancy Grace Roman Space Telescope Galactic Bulge Time Domain Survey.

Context: Solar flares accelerate electrons, creating non-thermal energy distributions. However, the acceleration sites and dominant acceleration mechanisms remain largely unknown. Aims: We study the characteristics of electron acceleration and subsequent non-thermal energy distribution in a 2D coronal plasmoid-mediated reconnecting current sheet. Methods: We used test particles and the guiding centre approximation to transport electrons in a static coronal 2D fan-spine topology magnetohydrodynamic (MHD) snapshot. The snapshot was from a Bifrost simulation that featured plasmoid-mediated reconnection at a current sheet. To sample initial particle conditions that lead to non-thermal energies, we used importance sampling. In this way, the characteristics of the non-thermal electrons were statistically representative of the MHD plasma. Results: The energy distribution of the electrons forms a non-thermal power law that varies with our tolerance of the guiding centre approximation's validity, from no obvious power law to a power law with an exponent of -4 (the power law also depends on the statistical weighing of the electrons). The non-thermal electrons gain energy through a gradual betatron acceleration close to magnetic null points associated with plasmoids. Conclusions: In this static, asymmetric, coronal, 2D fan-spine topology MHD configuration, non-thermal electron acceleration occurs only in the vicinity of null points associated with magnetic gradients and electric fields induced by plasmoid formation and ejection. However, the guiding centre approximation alone is not sufficient to properly estimate the shape of the non-thermal power law since, according to our results, electron acceleration is correlated with the adiabaticity of the particles' motion. The results also show that the particle power law formation is biased by the test particle sampling procedure.

We present \textit{JWST} NIRSpec and MIRI MRS observations of the central kiloparsec of M58 (NGC 4579), a nearby LINER galaxy hosting a low-luminosity AGN (LLAGN; $L_\mathrm{bol} \sim 10^{42}$ erg s$^{-1}$) with a low-power jet. These data provide an unprecedented view of the warm molecular gas phase and reveal clear signatures of feedback. We detect 44 H$_2$ lines, including bright pure rotational lines (S(1)-S(18)) and rovibrational lines up to $\nu=2$, probing a wide range of excitation conditions. Excitation diagrams show that rotational lines follow a power-law temperature distribution with an exponential cutoff, consistent with heating by low-velocity shocks. H$_2$ rovibrational lines deviate from thermal models primarily because of sub-thermal excitation at low density. Additionally, there may be a 10% contribution by AGN X-ray heating in the nucleus. The dust lanes associated with the spiral inflow appear dynamically undisturbed but show signs of shock heating, while the inner $\sim$200 pc exhibits turbulent kinematics produced by outflowing molecular gas. These results reveal the subtle yet measurable impact of LLAGN feedback on the interstellar medium, demonstrating that even weak, vertically oriented jets and low radiative accretion rates can perturb molecular gas and regulate nuclear reservoirs. This study highlights JWST's transformative ability to uncover hidden modes of AGN feedback.

This article details the optimisation and the characterisation of the hologram described in a companion paper published in 2021, which showed the superiority of a holographic optical element over a periodic grating as a disperser installed in the path of a converging beam on an on-axis detector (unbent spectrograph) for slitless spectroscopy. In this article, we describe in detail the development and optimisation of the final optical holographic element installed on the spectrograph of the auxiliary telescope (AuxTel) at the Rubin-LSST observatory. After recalling the general principle of a hologram used as a dispersing and focusing element, we describe the technical resources - optical bench and sky measurements - and modeling tools that enabled us to determine the optimum production parameters for the AuxTel hologram after 4 prototyping phases. We also describe the on-sky verifications and measurements carried out with various telescopes. Thanks to these various techniques, we have succeeded in obtaining a diffraction efficiency in the first order close to the maximum theoretically possible with our thin-type hologram. This hologram has been in place on AuxTel's spectrograph since February 2021, and has since given full satisfaction, coupled with analysis software adapted to slitless spectroscopy.

Calcium-rich gap transients are a faint, fast-evolving class of supernovae that show strong nebular Ca emission lines. Their progenitor systems are uncertain, but they are often associated with old and quiescent host galaxies. In this work, we compare the properties of the hosts of hydrogen-poor Ca-rich gap transients to the hosts of 3 other classes of supernova (SNe): normal Type Ia, 91bg-like, and Type II. We use data from the Zwicky Transient Facility (ZTF) Census of the Local Universe (CLU) experiment to build up our 4 SNe samples and identify the host galaxies. A combination of precomputed host properties from the CLU catalog and those derived from SED fitting are used to characterize each host's stellar mass, star formation rate, and specific star formation rate (sSFR). We find that the hosts of Ca-rich gap transients and 91bg-like SNe occupy a similar parameter space of mass and sSFR, and are more massive and quiescent compared to the hosts of Type Ia and Type II SNe. Additionally, we construct delay time distributions (DTDs) for our 4 samples, finding that Ca-rich gap transients and 91bg-like SNe have the longest peak delay times $\sim 10^4$ Myr, compared to the peak delay times of Type Ia SNe ($\sim 10^3$ Myr) and Type II SNe ($\sim 10$ Myr). The similarity of host environment and DTDs for Ca-rich gap transients and 91bg-like SNe motivates further analysis of the relationship of these two transient classes.

With the launch of the James Webb Space Telescope, we are firmly in the era of exoplanet atmosphere characterization. Understanding exoplanet spectra requires atmospheric chemical and climate models that span the diversity of planetary atmospheres. Here, we present a more general chemical and climate model of planetary atmospheres. Specifically, we introduce the open-source, one-dimensional photochemical and climate code Photochem, and benchmark the model against the observed compositions and climates of Venus, Earth, Mars, Jupiter and Titan with a single set of kinetics, thermodynamics and opacities. We also model the chemistry of the hot Jupiter exoplanet WASP-39b. All simulations are open-source and reproducible. To first order, Photochem broadly reproduces the gas-phase chemistry and pressure-temperature profiles of all six planets. The largest model-data discrepancies are found in Venus's sulfur chemistry, motivating future experimental work on sulfur kinetics and spacecraft missions to Venus. We also find that clouds and hazes are important for the energy balance of Venus, Earth, Mars and Titan, and that accurately predicting aerosols with Photochem is challenging. Finally, we benchmark Photochem against the popular VULCAN and HELIOS photochemistry and climate models, finding excellent agreement for the same inputs; we also find that Photochem simulates atmospheres 2 to 100 time more efficiently. These results show that Photochem provides a comparatively general description of atmospheric chemistry and physics that can be leveraged to study Solar System worlds or interpret telescope observations of exoplanets.

Cold dark matter (CDM) can be thought of as a 2D (or 3D) sheet of particles in 4D (or 6D) phase-space due to its negligible velocity dispersion. The large-scale structure, also called the cosmic web, is thus a result of the topology of the CDM manifold. Initial crossing of particle trajectories occurs at the critical points of this manifold, forming singularities that seed most of the collapsed structures. The cosmic web can thus be characterized using the points of singularities. In this context, we employ catastrophe theory in 2D to study the motion around such singularities and analytically model the shape of the emerging structures, particularly the pancakes, which later evolve into halos and filaments-the building blocks of the 2D web. We compute higher-order corrections to the shape of the pancakes, including properties such as the curvature and the scale of transition from their C to S shape. Using Gaussian statistics (with the assumption of Zeldovich flow) for our model parameters, we also compute the distributions of observable features related to the shape of pancakes and their variation across halo and filament populations in 2D cosmologies. We find that a larger fraction of pancakes evolve into filaments, they are more curved if they are to evolve into halos, are dominantly C-shaped, and the nature of shell-crossing is highly anisotropic. Extending this work to 3D will allow testing of predictions against actual observations of the cosmic web and searching for signatures of non-Gaussianity at corresponding scales.

Knowing the composition of Jupiter's atmosphere is crucial for constraining Jupiter's bulk metallicity and formation history. Yet, constraining Jupiter's atmospheric water abundance is challenging due to its potential non-uniform distribution. Here, we explicitly resolve the water hydrological cycle in Jupiter's mid-latitudes using high-resolution simulations. Falling precipitation leads to a significant large-scale depletion of water vapor beneath the lifting condensation level. A non-uniform water vapor distribution emerges in the mid-latitude simulation with a changing Coriolis parameter across latitudes and spatially uniform cooling and heating. Water abundance at the 7-bar level varies by up to a factor of ten across latitudes, from sub-solar to super-solar values. We propose that nonlinear large-scale eddies and waves tend to drift air parcels across latitudes along constant potential vorticity (PV) surfaces, thereby sustaining latitudinal dependencies in water vapor and the interplay between water distribution and large-scale dynamics. Therefore, water distribution is influenced by the vertical structure of density stratification and changing Coriolis parameter across Jupiter's mid-latitudes, as quantified by PV. Additionally, the water hydrological cycle amplifies the specific energy of air parcels through the latent heat effect, thereby slowing down vertical mixing with a latent heat flux. The horizontal gradient of water is expected to be more pronounced with a super-solar water abundance. We suggest that similar interplays between precipitating condensates, planetary rotation, and distribution of condensable species generally exist in the weather layer of fast-rotating giant planets. The ongoing Juno mission and future Uranus mission may further reveal the non-uniform distribution of condensed species and their interplay with large-scale dynamics.

The October Draconid meteor shower, produced by comet 21P/Giacobini-Zinner, is notorious for rare but intense outbursts, some exceeding rates of about 10 000 meteors per hour. In 2025, Earth will encounter young trails ejected by the comet in 2005 and 2012, producing a meteor outburst and providing a rare opportunity to probe their structure and benchmark meteoroid stream models. We present predictions from three independent dynamical models (NIMS, MSFC, Sisyphus), calibrated against updated activity profiles including the newly observed 2019 and 2024 outbursts. All simulations predict enhanced activity on 2025 October 8, dominated by faint meteors (m < 0.01 g; +4 mag and fainter) primarily detectable by radar. Our best estimate is a radar outburst near 15:00 - 16:00 UT, driven mainly by the 2012 trail with a possible minor contribution from 2005. The 2025 Draconids may represent one of the strongest radar dominated outbursts of the decade. Coordinated observing campaigns, especially radar measurements across the Northern Hemisphere and optical coverage from Asia, will be essential to validate these forecasts, constrain the dust environment of comet 21P, and improve future predictions of young meteoroid trails.

Elemental abundances in solar flares are observed to vary both spatially and temporally, but the underlying mechanisms remain poorly understood. There is an interplay between advection and the preferential acceleration of low first ionization potential (FIP) elements that likely shapes the observed abundance distributions. Models of the FIP effect predict enhancements near loop footpoints that diffuse upward over time. We simulate strong evaporation events that advect this low-FIP enhancement into the corona. When the enhancement is sharply peaked, the corona does not become fractionated, exhibiting only a localized abundance peak near the loop apex that facilitates coronal rain formation. In contrast, a broad enhancement with relatively weak heating yields a uniformly fractionated corona, which is not sufficient for coronal rain formation. As the heating rate increases, the low-FIP material is increasingly compressed toward the loop apex, and rain is able to form. These results suggest a potential observational correlation between the presence and amount of coronal rain, the strength of flare heating, and the fractionation process itself.

Fulfilling the science goals of the Simons Observatory, a state-of-the-art cosmic microwave background (CMB) experiment, has required deploying tens of thousands of superconducting bolometers. Reading out data from the observatory's more than 67,000 transition-edge sensor (TES) detectors while maintaining cryogenic conditions requires an effective multiplexing scheme. The SLAC microresonator radio frequency (SMuRF) electronics have been developed to provide the warm electronics for a high-density microwave frequency multiplexing readout system, and this system has been shown to achieve multiplexing factors on the order of 1,000. SMuRF has recently been deployed to the Simons Observatory, which is located at 5,200 m on Cerro Toco in Chile's Atacama Desert. As the SMuRF system is exposed to the desert's diurnal temperature swings, resulting phase drift in RF transmission lines may introduce a systematic signal contamination. We present studies of phase drift in the room-temperature RF lines of the Simons Observatory's 6 m large-aperture telescope, which hosts the largest deployment to date of TES microwave frequency multiplexing to a single telescope. We show that these phase drifts occur on time scales which are significantly longer than sky scanning, and that their contribution to on-sky in-transition detector noise is within the readout noise budget.

Magnetic fields influence the structure and evolution of protostellar systems, thus understanding their role is essential for probing the earliest stages of star formation. We present ALMA Band 3 and 6 polarized continuum observations at $\sim$0.5$^{\prime \prime}$ resolution toward the Class 0 protostellar system HH 211. Three dust filaments ($\sim$4000 au in length) are found in the HH 211 protostellar envelope, two of which are aligned with core-scale ($\sim$10,000 au) magnetic fields detected by previous JCMT observations. This result suggests that the formation of the dust filaments may be influenced by magnetic fields. In the inner envelope ($\sim$1000 au), we detect a clear hourglass-shaped magnetic field morphology near the protostar and toroidal fields along the outflow directions. We also estimate the line-of-sight-averaged temperature and column density distributions in the inner envelope and find that the temperature is higher in the east, while the column density is enhanced in the southern and western regions. The southern dense regions of the inner envelope may trace either outflow cavity walls, due to their alignment with the outflow, or possible infalling channels in the midplane, given the close correspondence between the observed magnetic fields and the predicted infall trajectories.

The Hector Galaxy Survey is a new optical integral field spectroscopy (IFS) survey currently using the AAT to observe up to 15,000 galaxies at low redshift ($z < 0.1$). The Hector instrument employs 21 optical fibre bundles feeding into two double-beam spectrographs to enable wide-field multi-object IFS observations of galaxies. To efficiently process the survey data, we adopt the data reduction pipeline developed for the SAMI Galaxy Survey, with significant updates to accommodate Hector's dual-spectrograph system. These enhancements address key differences in spectral resolution and other instrumental characteristics relative to SAMI, and are specifically optimised for Hector's unique configuration. We introduce a two-dimensional arc fitting approach that reduces the RMS velocity scatter by a factor of 1.2--3.4 compared to fitting arc lines independently for each fibre. The pipeline also incorporates detailed modelling of chromatic optical distortion in the wide-field corrector, to account for wavelength-dependent spatial shifts across the focal plane. We assess data quality through a series of validation tests, including wavelength solution accuracy, spectral resolution, throughput characterisation, astrometric precision, sky subtraction residuals, and flux calibration stability (4\% systematic offset when compared to Legacy Survey fluxes). We demonstrate that Hector delivers high-fidelity, science-ready datasets, supporting robust measurements of galaxy kinematics, stellar populations, and emission-line properties, and provide examples. Additionally, we address systematic uncertainties identified during the data processing and propose future improvements to enhance the precision and reliability of upcoming data releases. This work establishes a robust data reduction framework for Hector, delivering high-quality data products that support a broad range of extragalactic studies.

Planet formation occurs within the same molecular cloud as the host star, suggesting a link between the elemental abundances of star and the planet. Exoplanet atmosphere studies often assume solar abundances for host stars, however, specific host star abundances might lead to more accurate constraints. In this work, we perform sensitivity studies for a metal rich stellar host HD 149026 and its exoplanet HD 149026b, to understand the effect of solar versus stellar abundance choice on the $P$-$T$ profiles, equilibrium chemical abundances and emission spectra, using self-consistent atmosphere models. We find that the differences are dependent on the model parameters, particularly C/O ratio, and for HD 149026b the difference in the eclipse depth is maximum $\sim$80 ppm, for C/O between 0.75-0.85. Recent JWST NIRCam observations of HD 149026b have yielded widely varying metallicity ranges, highly super-solar (59-275$\times$) using chemical equilibrium retrievals and 12-31$\times$ solar using self-consistent models, both using solar abundances. In this work, we constrain the metallicity of HD 149026b to be 53-113$\times$ solar, with solar abundances and 39-78$\times$ stellar, with stellar abundances. We constrain the self-consistent $P$-$T$ profile of HD 149026b to be substantially cooler (upto 500 K) than the self-consistent best-fit model in the previous work, in the emission spectra probed region, thus requiring higher CO$_2$ abundance to explain the observations, leading to comparatively higher metallicity constraint. We find that the inclusion of Fe opacity in computing self-consistent $P$-$T$ profiles for HD 149026b in our models is the major reason for these differences. We constrain the C/O ratio to 0.47-0.68 and the heat redistribution factor to 0.70-0.76, indicating higher heat redistribution than previously estimated.

We present updated observational constraints on the spatially flat $\phi$CDM model, where dark energy is described by a minimally coupled scalar field $\phi$ with an inverse power-law potential $V=V_0 \phi^{-\alpha}$. Using Planck 2018 CMB temperature, polarization (P18), and lensing power spectra (lensing), along with a compilation of non-CMB data including baryon acoustic oscillation, type Ia supernova, Hubble parameter, and growth rate measurements, we constrain $\phi$CDM and $\phi$CDM+$A_L$ models where $A_L$ is the CMB lensing consistency parameter. The scalar field parameter $\alpha$, which governs dark energy dynamics, is more tightly constrained by non-CMB data than by CMB data alone. For the full dataset, we obtain $\alpha = 0.055 \pm 0.041$ in the $\phi$CDM model and $\alpha = 0.095 \pm 0.056$ in the $\phi$CDM+$A_L$ model, mildly favoring evolving dark energy over a cosmological constant by $1.3\sigma$ and $1.7\sigma$. The Hubble constant is $H_0=67.55_{-0.46}^{+0.53}$ km s$^{-1}$ Mpc$^{-1}$ in the $\phi$CDM model, consistent with median statistics and some local determinations, but in tension with other local determinations. The constraints for matter density and clustering amplitude ($\Omega_m = 0.3096 \pm 0.0055$, $\sigma_8 = 0.8013_{-0.0067}^{+0.0077}$) of the flat $\phi$CDM model statistically agree with $\Lambda$CDM model values. Allowing $A_L$ to vary reduces tensions between CMB and non-CMB data, although we find $A_L = 1.105 \pm 0.037$, $2.8\sigma$ higher than unity, consistent with the excess smoothing seen in Planck data. Model comparison using AIC and DIC indicates that the $\phi$CDM model provides a fit comparable to $\Lambda$CDM, with the $\phi$CDM+$A_L$ slightly preferred. Overall, while the $\Lambda$CDM model remains an excellent fit, current data leave open the possibility of mildly evolving quintessence-like dynamical dark energy.

Polarization observations of the Milky Way and many other spiral galaxies have found a close correspondence between the orientation of spiral arms and magnetic field lines on scales of hundreds of parsecs. This paper presents polarization measurements at 214 $\mu$m toward ten filamentary candidate ``bones" in the Milky Way using the High-resolution Airborne Wide-band Camera (HAWC+) on the Stratospheric Observatory for Infrared Astronomy (SOFIA). These data were taken as part of the Filaments Extremely Long and Dark: A Magnetic Polarization Survey (FIELDMAPS) and represent the first study to resolve the magnetic field in spiral arms at parsec scales. We describe the complex yet well-defined polarization structure of all ten candidate bones, and we find a mean difference and standard deviation of $-74^{\circ} \pm 32^{\circ}$ between their filament axis and the plane-of-sky magnetic field, closer to a field perpendicular to their length rather than parallel. By contrast, the 850 $\mu$m polarization data from \textit{Planck} on scales greater than 10 pc show a nearly parallel mean difference of $3^{\circ} \pm 21^{\circ}$. These findings provide further evidence that magnetic fields can change orientation at the scale of dense molecular clouds, even along spiral arms. Finally, we use a power law to fit the dust polarization fraction as a function of total intensity on a cloud-by-cloud basis and find indices between $-0.6$ and $-0.9$, with a mean and standard deviation of $-0.7 \pm 0.1$. The polarization, dust temperature, and column density data presented in this work are publicly available online.

We present on results of a spatially resolved spectral analysis of G1.9+0.3, the youngest known supernova remnant in the Galaxy. The X-ray spectra are well described by synchrotron emission from a power-law electron distribution with an exponential cutoff. We found a cutoff energy $\epsilon_0 \sim 1 ~ \rm{keV}$ in both the radio bright rim and the X-ray bright rims. In the loss-limited case, the cutoff energy depends on the shock velocity $v_{\rm{sh}}$ and the Bohm factor $\eta$, following the relation $\epsilon_0 \propto v_{\rm{sh}}^2 \eta^{-1} $. Our analysis shows that $\eta$ ranges from 2 to 4 in the radio rim and from 12 to 15 in the X-ray rims. This suggests that the magnetic field in the radio rim is more turbulent than in the X-ray rims. The presence of CO clouds along the radio rim likely contributes to this difference. Interaction between the shock and these clouds can slow the shock down and generate turbulent eddies. The resulting turbulence eddies can amplify the magnetic field. We propose that the strong radio emission from the radio rim is primarily due to this amplified magnetic field. In contrast, a CO cloud located in the south-west appears to lie in the foreground, as indicated by its low turbulence and the absence of shock deceleration.

We present the result of a comparison between the dark matter distribution inferred from weak gravitational lensing and the observed galaxy distribution to identify dark structures with a high dark matter-to-galaxy density ratio. To do this, we use weak lensing convergence maps from the Dark Energy Survey Year 3 data, and construct corresponding galaxy convergence maps at $z\lesssim1.0$, representing projected galaxy number density fluctuations weighted by lensing efficiency. The two maps show overall agreement. However, we could identify 22 regions where the dark matter density exhibits an excess compared to the galaxy density. After carefully examining the survey depths and proximity to survey boundaries, we select seven of the most probable candidates for dark structures. This sample provides valuable testbeds for further investigations into dark matter mapping. Moreover, our method will be very useful for future studies of dark structures as large-scale weak-lensing surveys become available, such as the $\textit{Euclid}$ mission, the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST), and the Nancy Grace Roman Space Telescope.

The possibility of neutron decay into dark particles has been proposed as a way to resolve a growing discrepancy between two different measurements of the neutron lifetime. The most popular formulation is a dark sector consisting of a dark baryon $\chi$ and a dark scalar $\phi$, where a neutron in vacuum decays about 1% of the time via the channel $n\rightarrow \chi+\phi$. In this work, we consider the effect of this additional neutron decay channel on transport in neutrons star mergers. We find that the neutron dark decay rate in medium is quite slow, and thus the dark baryons modify the dense matter equation of state in a way that decreases the Urca bulk viscosity by, at most, a factor of 2-3. However, if the neutron dark decay was to occur more rapidly, then the bulk viscosity at merger temperatures of tens of MeV would be strongly enhanced, potentially rapidly damping oscillations in merger environments and therefore providing a signature of slowly equilibrating matter in the merger.

The abundance and mass function of primordial black holes (PBHs) are often estimated using the Press-Schechter (PS) formalism. In the case of halo formation, the PS formalism suffers from the miscounting of regions collapsing into halos, known as the cloud-in-cloud problem, which is usually corrected by introducing a multiplicative `fudge factor 2'. By analogy, this factor has sometimes been applied to PBH calculations, although its validity has remained unsettled. We reformulate the PS approach for PBHs within the excursion-set framework, where the smoothed density contrast undergoes a stochastic random walk as the smoothing scale varies and collapse is identified with the first threshold crossing. While the halo case is described by a Markovian process, we show that the PBH case is non-Markovian, even when the sharp-k filter Window function is adopted. Decomposing the total collapse probability into two distinct components of the stochastic motion, we numerically confirm that their contributions are exactly equal in the case of halo formation, justifying the fudge factor. For PBHs, however, we demonstrate that this equality no longer holds, and consistent inclusion of both contributions is essential to ensure a positive-definite mass function. Our results clarify the origin of the ambiguity surrounding the fudge factor and establish a robust theoretical foundation for PBH abundance calculations.

Stars captured by black holes (BHs) can be tore apart by strong tidal force, producing electromagnetic flares. Some 100 tidal disruption events (TDEs) have been observed, involving invariably normal gaseous stars whose debris falls onto the BH fueling the flares over years. White dwarfs (WDs)-the most prevalent compact stars a million times denser and thus tougher than gaseous stars-can only be disrupted by intermediate-mass black holes (IMBHs) of 10^2-10^5 solar masses. WD-TDEs are predicted to generate more powerful and short-lived flares, but their evidence has been lacking. Here we report observations of a fast, luminous X-ray transient EP250702a. Its one-day-long peak showed strong recurrent flares extending to several tens of MeV in gamma-rays, indicating relativistic jet emission. The jet X-rays dropped sharply from exceeding 3 x 10^49 to around 10^44 erg/s within 20 days. These characteristics are inconsistent with any known transient phenomena other than a jetted-TDE evolving within a short timespan previously unseen-indicating the disruption of a white dwarf by an IMBH. At late times, a new soft component progressively dominates the X-ray spectrum, exhibiting extreme super-Eddington luminosity, possibly from an accretion disc. WD-TDEs open a new window to study elusive IMBHs and the otherwise invisible interior of degenerate stars.

Galactic $\gamma$-ray sources can be produced by either high-energy protons via proton-proton collisions or electrons/positrons via inverse Compton scattering. Distinguishing between the hadronic and leptonic origin of $\gamma$-ray emission in Galactic sources remains challenging. Measurements of non-thermal X-ray spectra of these sources, which could originate from primary electrons in the leptonic scenario or secondary electrons/positrons in the hadronic scenario, have been suggested as an efficient way of discriminating between these scenarios. In this work, we investigate the morphology of the X-ray emission from secondary electrons/positrons. By calculating the surface brightness profile and the photon index profile of X-ray emission, we find that secondary electrons produce a distinctively flat X-ray surface brightness profile. Our results suggest that, in addition to the X-ray spectrum, the X-ray morphology is crucial to determine the radiation mechanism of ultrahigh-energy $\gamma$-ray sources and help to identify sources of PeV cosmic rays.

We consider a generalization of the classical nonrelativistic Störmer problem, describing the motion of charged particles in a purely magnetic dipole field, by taking into account the effects of the dissipation, assumed to be of friction type, proportional to the velocity of the particle, and of the presence of stochastic forces. In the presence of dissipative/stochastic effects, the motion of the particle in the magnetic dipole field can be described by a generalized Langevin type equation, which generalizes the standard Lorentz force equation. We perform a detailed numerical analysis of the dynamical behavior of the particles in a magnetic dipolar field in the presence of dissipative and stochastic forces, as well as of the electromagnetic radiation patterns emitted during the motion. The effects of the dissipation coefficient and of the stochastic force on the particle motion and on the emitted electromagnetic power are investigated, and thus a full description of the spectrum of the magnetic dipole type electromagnetic radiation and of the physical properties of the motion is also obtained. The power spectral density of the emitted electromagnetic power is also obtained for each case, and, for all considered Störmer type models, it shows the presence of peaks in the radiation spectrum, corresponding to certain intervals of the frequency.

The properties of radial nonlinear pulsations of massive blue stars are computed with the MESA software instrument in its dynamical mode. Pulsational instabilities could be computationally detected and followed if the evolutionary timestep was reduced to a fraction of the unfolding pulsation period. Stellar variability was recovered in regions on the HR plane that have been studied before and that are known to host LBVs and relatives. Mode properties are analyzed on the full stellar-evolution models, which are not in thermal equilibrium. Despite persistent numerical shortcomings, it appears possible to compute strange-mode - like pulsations of massive blue stars with MESA.

The search for gamma-ray counterparts to gravitational-wave events with the CALET Gamma-ray Burst Monitor (CGBM) requires accurate and robust background modeling. Previous CALET observing runs (O3 and O4) relied on averaged pre/post-event baselines or low-order polynomial fits, approaches that neglect correlated noise, temporal non-stationarity, and the propagation of background uncertainty into derived flux upper limits. These simplifications can lead to reduced sensitivity to faint or atypical transients. In this work, we present a novel Bayesian framework for background estimation based on Gaussian Process (GP) regression and change-point modeling. Our approach captures correlated structures in the detector background, quantifies predictive uncertainties, and propagates them into both detection statistics and Bayesian credible upper limits. We demonstrate, using archival CALET time-tagged event data and simulated signal injections, that our method improves sensitivity to weak short-duration bursts by up to an order of magnitude compared to traditional polynomial fits. This probabilistic background treatment enables a more physically robust interpretation of non-detections and offers a scalable, real-time compatible extension for future joint multi-messenger searches. All codes used in this paper are available at this https URL.

Tidal Disruption Events (TDEs) are astrophysical phenomena arising when stars are disrupted by supermassive black holes. The Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST), with its unprecedented depth and cadence, will detect thousands of TDEs, motivating the need for robust photometric classifiers capable of efficiently distinguishing these events from other extragalactic transients. We aim to develop and validate a machine learning pipeline for photometric TDE identification in LSST-scale datasets. Our classifier is designed to provide high precision and recall, enabling the construction of reliable TDE catalogs for multi-messenger follow-up and statistical studies. Using the second Extended LSST Astronomical Time Series Classification Challenge (ELAsTiCC2) dataset, we fit Gaussian Processes (GP) to light curves for feature extraction (e.g., color, rise/fade times, GP length scales). We then train and tune boosted decision-tree models (XGBoost) with a custom scoring function emphasizing high-precision recovery of TDEs. Our pipeline is tested on a diverse simulation of transient and variable events, including supernovae, active galactic nuclei, and superluminous supernovae. We achieve high precision (up to 95%) while maintaining competitive recall (about 72%) for TDEs, with minimal contamination from non-TDE classes. Key predictive features include post-peak colors and GP hyperparameters, reflecting characteristic timescales and spectral behaviors of TDEs. Our photometric classifier provides a practical and scalable approach to identifying TDEs in forthcoming LSST data. By capturing essential color and temporal properties through GP-based feature extraction, it enables efficient construction of clean TDE candidate samples.

It is generally believed that the electron-capture reactions happen when the oxygen-neon (ONe) cores grow in masses close to the Chandrasekhar limit, leading to the formation of neutron stars (NSs) via electron-capture supernovae (EC-SNe). EC-SNe are predicted to be the most likely short-lived and faint optical transients, and a small ejecta mass is expected during the collapse. This kind of SNe provide an alternative channel for producing isolated NSs and NS systems, especially for the formation of X-ray binaries and double NSs. However, there are still some uncertainties for the origin of EC-SNe. In this article, we review recent studies on the two classic progenitor channels of EC-SNe, i.e., the single star channel and the binary star channel. In the single star channel, EC-SNe can happen in super asymptotic giant branch stars or He stars, whereas in the binary star channel EC-SNe can occur in He stars in binaries (including He star+MS systems and NS+He star systems) or accretion-induced collapse in white dwarf binaries (including the single-degenerate scenario and the double-degenerate scenario). Recent progress on the two progenitor channels is discussed, including the initial parameter range for EC-SNe, the evolutionary paths to EC-SNe, related objects, and some observational constraints, etc. We also discuss the formation of double NSs through NS+He star binaries, in which the He star companion experiences an EC-SN. Research on EC-SNe is at a pivotal stage, with key theoretical uncertainties and observational challenges requiring integrated modeling and multi-wavelength observations for robust identification.

CSS100217 is considered a peculiar tidal disruption event (TDE) candidate occurring in an active galactic nucleus (AGN). Unlike typical TDEs, where the post-flare luminosity is equal to that pre-flare, CSS100217 decayed to $\sim$ 0.4 magnitudes fainter than its pre-flare V band level. In this manuscript, we propose an obscured TDE model to explain the light curve of CSS100217. Assuming that the time-dependent obscuration, caused by the TDE unbound stellar debris, or by nuclear clouds moving around the supermassive black hole (SMBH), follows a Weibull distribution, we find that the light curve of CSS100217 can be described by the tidal disruption of a $4.6_{-0.9}^{+0.9}{\rm M_\odot}$ main-sequence star by a $3.3_{-0.3}^{+0.3}\times10^7{\rm M_\odot}$ black hole. The total energy of the event derived from our fit is $7.23\times10^{53}$ ergs and about 1.38 ${\rm M_\odot}$ of debris mass is accreted by the central SMBH. The model indicates that the contribution of the host galaxy to the observed pre-flare optical luminosity is not-significant compared to that of the AGN, which is consistent with the results of the spectral analysis. These results suggest that obscuration may play an important role in explaining the unusual TDE-like variability observed in CSS100217.

This paper reports the discovery and follow-up of four candidate redback spider pulsars: GPM J1723-33, GPM J1734-28, GPM J1752-30 and GPM J1815-14, discovered with the Murchison Widefield Array (MWA) from an imaging survey of the Galactic Plane. These sources are considered to be redback candidates based on their eclipsing variability, steep negative spectral indices, and potential Fermi $\gamma$-ray associations, with GPM J1723-33 and GPM J1815-14 lying within a Fermi 95% error ellipse. Follow-up pulsation searches with MeerKAT confirmed pulsations from GPM J1723-33, while the non-detections of the other three are likely due to scattering by material ablated from their companion stars. We identify possible orbital periods by applying folding algorithms to the light curves and determine that all sources have short orbital periods (<24 hours), consistent with redback spider systems. Following up on the sources at multiple radio frequencies revealed that the sources exhibit frequency-dependent eclipses, with longer eclipses observed at lower frequencies. We place broad constraints on the eclipse medium, ruling out induced Compton scattering and cyclotron absorption. Three sources are spatially consistent with optical sources in the Dark Energy Camera Plane Survey imaging, which may contain the optical counterparts. Each field is affected by strong dust extinction, and follow-up with large telescopes is needed to identify the true counterparts. Identifying potential radio counterparts to four previously unassociated Fermi sources brings us closer to understanding the origin of the unexplained $\gamma$-ray excess in the Galactic Centre.

A search for second-timescale optical transients is one of the frontiers of time-domain astronomy. However, it has been pointed out that reflections of sunlight from Earth-orbiting objects can also produce second-timescale ``glints.'' We conducted wide-field observations at 2 frames per second using Tomo-e Gozen on the 1.05 m Kiso Schmidt telescope. We identified 1554 point-source glints that appeared in only one frame (0.5 sec). Their brightness ranges from 11 to 16 mag, with fainter glints being more numerous. These glints are likely caused by satellites and space debris in high-altitude orbits such as the geosynchronous Earth orbit or highly elliptical orbits. Many glints brighter than 14 mag are associated with known satellites or debris with large apogees ($>$ 30,000 km). In contrast, most fainter glints are not associated with cataloged objects and may be due to debris with sizes of 0.3--1 m. The event rate of second-timescale glints is estimated to be $4.7 \pm 0.2\ {\rm deg^{-2}\ hr^{-1}}$ (average) and $9.0 \pm 0.3\ {\rm deg^{-2}\ hr^{-1}}$ (near the equator) at 15.5 mag. Our results demonstrate that high-altitude debris can represent a significant foreground in searches for second-timescale optical transients. They also imply that deep surveys such as Rubin/LSST will detect many of these glints in single-exposure images.

We report on the search for ultra-high-energy neutrinos from the prompt emission of gamma-ray bursts (GRBs) using Surface Detector (SD) data from Phase I of the Pierre Auger Observatory (2004-2021). A total of 570 GRBs occur within the most neutrino-sensitive field of view of the SD, considering both Earth-skimming and downward-going detection channels. For this purpose, GRB neutrino emission has been modeled using the numerical software NeuCosmA, incorporating gamma-ray measurements and inferred parameters such as the jet Lorentz factor and the minimum variability time scale. No neutrino candidates were found, and upper limits were obtained by stacking the individual GRB neutrino fluences. These limits are complementary to those of IceCube and ANTARES and provide the strongest constraints on prompt GRB neutrino fluence above $10^{18}$ eV. Additionally, limits on GRB fluence in alternative models of neutrino production have been derived using Auger data.

In this paper, we investigate the impact of higher-order distortions on the precise measurement of weak gravitational lensing shear and flexion. We begin by defining generalized higher-order distortions and outlining methods for measuring them. Then, using several lens models, we examine how these distortions affect shear and flexion measurements. Our results show that neglecting higher-order distortions can introduce systematic errors of a few percent in both shear and flexion measurements, indicating that these effects cannot be ignored. Although the strength of these errors depends on factors such as lensing strength and the size of background sources, we demonstrate that simultaneous measurement of higher-order distortions can reduce the systematic errors to below 1% in most cases.

Context: Investigating the vertical distribution of molecular content in protoplanetary disks remains difficult in most disks mildly inclined along the line of sight. In contrast, edge-on disks provide a direct (tomographic) view of the 2D molecular brightness. Aims: We study the radial and vertical molecular distribution as well as the gas temperature and density by observing the Keplerian edge-on disk surrounding the Flying Saucer, a Class II object located in Ophiuchus. Methods: We use new and archival ALMA data to perform a tomography of $^{12}$CO, $^{13}$CO, C$^{18}$O, CN, HCN, CS, H$_2$CO, c-C$_3$H$_2$, N$_2$D$^+$, DCN and $^{13}$CS. We analyze molecular tomographies and model data using the radiative transfer code DiskFit. Results: We directly measure the altitude above the mid-plane for each observed species. For the first time, we unambiguously demonstrate the presence of a common molecular layer and measure its thickness: most molecules are located at the same altitude versus radius. Beyond CO, as predicted by chemical models, the CN emission traces the upper boundary of the molecular layer, whereas the deuterated species (DCN and N2D+) resides below one scale-height. Our best fits from DiskFit show that most observed transitions in the molecular layer are thermalized because their excitation temperature is the same, around 17-20 K. Conclusions: These long-integration observations clearly reveal a molecular layer predominantly located around 1-2 scale height, at a temperature above the CO freeze-out temperature. The deuterated molecules are closer to the mid-plane and N2D+ may be a good proxy for the CO snowline. Some molecules, such as CN and H2CO, are likely influenced by the disk environment, at least beyond the mm dust disk radius. The direct observation of the molecular stratification opens the door to detailed chemical modeling in this disk which appears representative of T Tauri disks.

The $\Lambda$CDM model has long served as the cornerstone of modern cosmology, offering an elegant and successful framework for interpreting a wide range of cosmological observations. However, the rise of high-precision datasets has revealed statistically significant tensions, most notably the Hubble tension and the $S_8$ discrepancy, which challenge the completeness of this standard model. In this context, we explore the $\Lambda_{\rm s}$CDM model-an extension of $\Lambda$CDM featuring a single additional parameter, $z_\dagger$, corresponding to a sign-switching cosmological constant. This minimal modification aims to alleviate key observational tensions without compromising the model's overall coherence. Recent findings present in the literature indicate that the $\Lambda_{\rm s}$CDM model not only provides a better fit to Lyman-$\alpha$ forest data for $z_\dagger < 2.3$, but also accommodates both the SH0ES measurement of $H_0$ and the angular diameter distance to the last scattering surface when 2D BAO data are included. We present a comprehensive analysis combining the full Planck 2018 CMB data, the Pantheon Type Ia Supernovae sample, and the recently released Baryon Acoustic Oscillation (BAO) measurements from the Dark Energy Spectroscopic Instrument (DESI). Our finding reveal that the Preliminary DESI results, a possible $3.9\sigma$ deviation from $\Lambda$CDM expectations, reinforce the importance of exploring such dynamic dark energy frameworks. In sum, our study underscores the potential of $\Lambda_{\rm s}$CDM to reconcile multiple cosmological tensions and sheds light on the role of upcoming high-precision observations in reshaping our understanding of the universe's expansion history and the nature of dark energy.

Emission lines of FeI and NiI are commonly found in the coma of solar system comets, even at large heliocentric distances. These atoms are most likely released from the surface of the comet's nucleus or from a short-lived parent. The presence of these lines in cometary spectra is unexpected because the surface blackbody equilibrium temperature is too low to allow the sublimation of refractory minerals containing these metals. These lines were also found in the interstellar comet 2I/Borisov which has a NiI/FeI abundance ratio similar to that observed in solar system comets. On average, this ratio is one order of magnitude higher than the solar Ni/Fe abundance ratio. Here, we report observations of the new interstellar comet 3I/ATLAS, which were carried out with the ESO Very Large Telescope equipped with the UVES spectrograph. Spectra were obtained at six epochs, at heliocentric distances ranging from 3.14 to 2.14 au. NiI was detected at all epochs. FeI was only detected at heliocentric distances smaller than 2.64 au. We estimated the NiI and FeI production rates by comparing the observed line intensities with those produced by a fluorescence model. Comet 3I exhibits a high production rate of NiI atoms as well as a high NiI/FeI ratio, making it exceptional when compared to solar system comets and 2I/Borisov. Additionally, we found that the NiI/FeI ratio decreases rapidly with decreasing heliocentric distance, suggesting that comet 3I could soon become indistinguishable from solar system comets in this respect. We interpreted these observations assuming that the NiI and FeI atoms were released through the sublimation of Ni(CO)$_4$ and Fe(CO)$_5$ carbonyls, which supports the presence of these species in the cometary material.

Dark matter (DM) subhalos offer critical tests of cosmological models through their abundance and properties, yet most remain undetectable due to their lack of stars. We investigate whether their presence leaves measurable imprints on the projected stellar density fields of dwarf spheroidal galaxies (dSphs). Building on literature $N$-body experiments, we show that subhalo interactions induce subtle out-of-equilibrium fluctuations appearing as density corrugations. In a CDM framework, these fluctuations are dominated by the most massive subhalos in the host halo. We develop a Fourier-based framework to quantify these features, identifying characteristic peaks in the spatial frequency spectrum that are well described by Voigt profiles. The peak parameters are sensitive to both the subhalo mass function and the number of stellar tracers. For the configurations tested, $N_{\star} \sim 10^5$ stars suffice to detect subhalo populations with $M_{\rm subhalo} \lesssim 10^6~\mathrm{M}_{\odot}$, while larger masses produce stronger and more complex signatures. We assess the feasibility of this technique by analyzing Gaia and HST data: in this context, the Fornax dwarf shows residual low-frequency structures resembling those in our controlled subhalo experiments, making it an interesting case for follow-up. Prospectively, wide-field surveys such as Euclid, the Nancy Grace Roman Space Telescope, and the Vera C. Rubin Observatory are expected to deliver stellar samples of $N_{\star} \sim 10^5$ per dwarf, offering compelling prospects for probing subhalo imprints. Our results introduce a novel pathway to constrain the subhalo mass function in dSphs, and motivate follow-up work that incorporates alternative DM models and additional dynamical perturbations.

CTA~1 is a composite supernova remnant featuring a shell structure and an inner Pulsar Wind Nebula. The shell is visible in the radio band, while Fermi has detected the radio-quiet pulsar PSR J0007+7303 at its core. Gamma-ray detectors such as LHAASO and VERITAS have detected TeV emission in the vicinity of the pulsar. However, the derived SEDs from LHAASO WCDA and VERITAS show significant discrepancies, which could be due to a complicated energy-dependent morphology not accounted for in the spectral analysis, and different angular resolution of the two experiments. CTA~1 has been a target for dedicated observations by the SST-1M telescopes, a pair of small-sized Imaging Atmospheric Cherenkov Telescopes (IACTs) capable of operating in both mono and stereo modes. Located at the Ondřejov Observatory in Czech Republic, these telescopes are sensitive to the high energy range of the gamma-ray spectrum, spanning from 1 to 300 TeV. To investigate the very high-energy emission of CTA~1, the SST-1Ms have accumulated approximately 30 hours of selected observations, aiming to further constrain the characteristics of the source's high energy emission, and to shed some light into the discrepancy between different experiments.

The peak model of structure formation was built more than fifty years ago with the aim to address the origin of dark matter halo rotation in the tidal torque theory (TTT). Paradoxically, it has allowed one to explain and reproduce all halo properties found in cosmological simulations except their rotation, which remains to be understood. With the present two Papers we remedy this anomaly. In Paper I we derived the angular momentum (AM) of protohalos centered on triaxial peaks of suited scale, taking into account that, to leading order, their density profile is smooth and homogeneous. Here we use that result to derive the AM of these objects, accounting for the fact that their actual density profile is slightly outward decreasing and lumpy so that they do not collapse monolithically at once, but progressively from inside out, undergoing mergers during the process. By monitoring in detail their resulting mass and AM growth, we characterize the spin distribution of final halos and the precise mass and radial distribution of their inner mean specific AM. The results obtained explain and reproduce the rotational properties of simulated halos.

Understanding interactions of binary systems on the red giant branch is crucial to understanding the formation of compact stellar remnants such as helium-core white dwarfs (He-WDs) and hot subdwarfs. However, the detailed evolution of such systems, particularly those with nearly identical components, remains under-explored. We aim to analyse the double-lined spectroscopic binary system BD+20 5391, composed of two red giant stars, in order to characterise its orbital and stellar parameters and to constrain its evolution. Spectroscopic data were collected between 2020 and 2025 using the Ondřejov Echelle Spectrograph and the Mercator Échelle Spectrograph. The time-resolved spectra were fitted with models to determine the radial velocity curve and derive the system's parameters. We then used the position of both stars in the Hertzsprung-Russell diagram to constrain the system's current evolutionary state, and we discuss potential outcomes of future interactions between the binary components. We find that the two stars in BD+20 5391 will likely initiate Roche lobe overflow (RLOF) simultaneously, leading to a double-core evolution scenario. The stars' helium core masses at RLOF onset will be almost identical, at 0.33 $\mathrm{M}_{\odot}$. This synchronised evolution suggests two possible outcomes: common envelope ejection, resulting in a short-period double He-WD binary, or a merger without envelope ejection. In the former case, the resulting double He-WD may merge later and form a hot subdwarf star. This study provides a valuable benchmark example for understanding the evolution of interacting red giant binaries, which will be discovered in substantial numbers in upcoming large-scale spectroscopic surveys.

We consider a 12-parameter cosmological model with non-phantom dynamical dark energy (NPDDE), where non-phantom implies that the equation of state (EoS) of dark energy (DE), $w(z)\geq-1$ for all redshifts $z$. Thus, the DE EoS covers the parameter space corresponding to the popular single scalar-field dark energy models, i.e., Quintessence. The cosmological model comprises 6 parameters of the $\Lambda$-Cold Dark Matter ($\Lambda$CDM) model, and additionally the dynamical DE EoS parameters ($w_0$, $w_a$), the scaling of the lensing amplitude ($A_{\rm lens}$), sum of the neutrino masses ($\sum m_\nu$), the effective number of non-photon relativistic degrees of freedom ($N_{\rm eff}$), and the running of the scalar spectral index ($\alpha_s$). We derive constraints on the parameters by combining the latest Dark Energy Spectroscopic Instrument (DESI) Data Release (DR) 2 Baryon Acoustic Oscillation (BAO) measurements with cosmic microwave background (CMB) power spectra from Planck Public Release (PR) 4, CMB lensing data from Planck PR4 and Atacama Cosmology Telescope (ACT) DR6, uncalibrated Type Ia supernovae (SNe) data from the Pantheon+ and Dark Energy Survey (DES) Year 5 (DESY5) samples, and Weak Lensing (WL) data from DES Year 1. Our major finding is that with CMB+BAO+WL and CMB+BAO+SNe+WL, we find 3$\sigma$+ evidence for $A_{\rm lens} >1$, indicating a higher than expected CMB lensing amplitude relative to the NPDDE prediction of unity. This implies that for cosmology to accommodate realistic quintessence-like dark energy models (as opposed to unrealistic phantom DE), one would also need to explain a relatively significant presence of the lensing anomaly.

We report an X-ray polarization degree (PD) of $8.8\pm1.4\%~(1\sigma)$ from the accretion-disc-corona (ADC) neutron-star system 2S 0921-630 (=V395 Car) observed with the Imaging X-ray Polarimetry Explorer (IXPE). The PD increases with energy, while the polarization angle (PA) varies significantly across the band. These trends are consistent with a high-inclination ADC geometry where the vertically extended disc blocks direct sight of the central X-ray source, and the observed X-rays are those scattered in an equatorial disc wind. We also find tentative PD variability in the 2--3 keV band. To interpret the time-averaged polarization, we build spectropolarimetric models by Monte Carlo radiation transfer simulation with column density distribution of thermal-radiative wind launched by X-ray irradiation of the outer disc under an axisymmetric geometry. The model combines boundary-layer emission, its disc reflection, and the disc continuum, each with its intrinsic polarization. Scattering of this composite spectrum in the wind reproduces both the observed PD and its increase with energy. However, the observed PA evolution is not captured, which may indicate departures from axisymmetry--e.g. misalignment between the inner disc (and/or neutron-star spin) and the outer disc/wind, or a weak disc warping.

GW200105 is a compact binary coalescence (CBC) event, consisting of a neutron star and a black hole, observed in LIGO-Virgo-KAGRA's (LVK's) third observing run (O3). Recent reanalyses of the event using state-of-the-art waveform models have claimed observation of signatures of an eccentric orbit. It has nevertheless been pointed out in the literature that certain physical or modified gravity effects could mimic eccentricity by producing a spurious non-zero eccentricity value, at a given reference frequency, when recovered with an eccentric waveform model. We recently developed a model-independent Eccentricity Evolution Consistency Test (EECT, S. A. Bhat et al. 2025) to identify such mimickers, by comparing the measured frequency $\textit{evolution}$ of eccentricity, $e(f)$, with that expected from General Relativity (GR). In this $\textit{Letter}$, we apply EECT to GW200105 and find that it satisfies EECT within 68% confidence. Our analysis therefore lends complementary support in favour of the eccentricity hypothesis, while also providing a novel test of the consistency of $e(f)$ with GR.

We study the white dwarf (WD) cooling sequence of the Galactic Globular Cluster (GGC) NGC 2808 by using deep near-UV data from the Hubble Space Telescope and theoretical models, to investigate if this cluster hosts an excess of WDs. Excess in WDs is a rare phenomenon that has been found to exist only in a few GGCs. We compared star counts from different evolutionary phases on the near-UV color-magnitude diagram to evolutionary times predicted by BaSTI models. The investigation was carried out over a region within a radii of 1.5 $\arcmin$ of the cluster center and a region of similar dimension located 5$\arcmin$ away. We find a WD excess of $\approx$ 60 - 70\% when comparing star counts and evolutionary models of the WD cooling sequence to the main-sequence turn-off, and by using different values and fractions of Helium enhancement. This excess decreases to $\approx$ 30 - 40\% when the WD cooling sequence is compared to the horizontal branch. The WD excess is slightly larger in the internal field that covers the cluster center; however, the difference with the external field is compatible within the uncertainties. We argue that this excess is possibly related to the existence of SCWDs and Helium-core WDs in NGC~2808, and might be directly associated to the extended blue horizontal branch of this GGC.

Understanding the link between outer giant planets (OGPs) and inner light planets (ILPs) is key to understanding planetary system formation and architecture. The correlation between these two populations of planets is debated both theoretically -- different formation models predict either a correlation or an anticorrelation -- and observationally. Several recent attempts to constrain this correlation have yielded contradictory results, due to small-number statistics and heterogeneous samples. We present an ongoing long-term observational effort with CORALIE, HARPS, and ESPRESSO to probe the ILP occurrence in systems with and without OGP. In this first article of a series, we discuss how, from the design to the observations, we ensured the homogeneity of the samples, both in terms of stellar properties and observing strategy. We also present the first three detections of ILPs in our OGP host sample. We find a 8.3 mE planet at 5.75 d around HD 23079, a 10.4 mE planet at 4.6 d around HD 196067, and we confirm the 7.5 mE planet at 3.98 d around HD 86226. While a rigorous statistical analysis of our samples will be performed in subsequent studies, the relatively low number of detections in our sample seems to contradict previous studies that found a strong OGP-ILP correlation.

We revisit the Cosmic Microwave Background (CMB) constraints on the spatial curvature of the Universe, assessing how they change when the curvature parameter and the primordial inflationary scalar spectrum are treated consistently within theoretically motivated frameworks. Instead of relying on the phenomenological parametrisation commonly used to capture curvature effects at the largest scales, we present a case study based on closed quadratic inflation, where the primordial spectrum is derived in full generality and in a gauge-invariant manner. Within this framework, we analyze both the $\texttt{plik}$ PR3 and $\texttt{CamSpec}$ PR4 Planck CMB likelihoods and find that the constraints on $\Omega_{\mathcal{K}}$ shift towards spatial flatness. In $\texttt{plik}$ the preference for $\Omega_{\mathcal{K}}<0$ decreases from $\gtrsim 3.5\sigma$ to $\sim 2.5\sigma$, while in $\texttt{CamSpec}$ it reduces to $\sim 2\sigma$. At large angular scales ($\ell < 10$), our model explains the low-$\ell$ power suppression anomaly, notably improving the fit to the quadrupole. However, the reduced preference for highly negative values of $\Omega_{\mathcal{K}}$ only partially accounts for the lensing anomaly at high multipoles, worsening the fit to the $\texttt{plik}$ spectrum at small scales. By contrast, in the $\texttt{CamSpec}$ PR4 spectrum, where the lensing anomaly is less pronounced, the model yields an overall improvement. Our analysis highlights a key conceptual point: closed-inflation models tie the curvature parameter to the inflationary dynamics and the primordial spectrum, enforcing consistency conditions that do not necessarily allow for the large deviations from flatness seen in phenomenological parametrisations. In the case of quadratic inflation, these restrictions reduce the apparent evidence for negative curvature reported by earlier analyses, while allowing for a mildly closed geometry.

We present a multiwavelength analysis of the central stellar pair of $\rho$ Oph, components A and B. Using recent high-resolution \textit{Chandra X-ray Observatory} observations, we demonstrate with high confidence that the dominant X-ray source is $\rho$ Oph B, while $\rho$ Oph A is comparatively X-ray faint. This result contrasts with earlier \textit{XMM-Newton} observations, which, due to limited spatial resolutions, attributed the X-ray emission to $\rho$ Oph A. An analysis of $\rho$ Oph B's X-ray light curves and spectra reveals properties more consistent with a cool star than a hot star. We therefore propose that $\rho$ Oph B is an Algol-like binary system, consisting of a B-type primary and an active, X-ray-emitting GK-type companion.

The boundary of solar system object discovery lies in detecting its faintest members. However, their discovery in detection catalogs from imaging surveys is fundamentally limited by the practice of thresholding detections at signal-to-noise (SNR) $\geq 5$ to maintain catalog purity. Faint moving objects can be recovered from survey images using the shift-and-stack algorithm, which coadds pixels from multi-epoch images along a candidate trajectory. Trajectories matching real objects accumulate signal coherently, enabling high-confidence detections of very faint moving objects. Applying shift-and-stack comes with high computational cost, which scales with target object velocity, typically limiting its use to searches for slow-moving objects in the outer solar system. This work introduces a modified shift-and-stack algorithm that trades sensitivity for speedup. Our algorithm stacks low SNR detection catalogs instead of pixels, the sparsity of which enables approximations that reduce the number of stacks required. Our algorithm achieves real-world speedups of $10$--$10^3 \times$ over image-based shift-and-stack while retaining the ability to find faint objects. We validate its performance by recovering synthetic inner and outer solar system objects injected into images from the DECam Ecliptic Exploration Project (DEEP). Exploring the sensitivity--compute time trade-off of this algorithm, we find that our method achieves a speedup of $\sim30\times$ with $88\%$ of the memory usage while sacrificing $0.25$ mag in depth compared to image-based shift-and-stack. These speedups enable the broad application of shift-and-stack to large-scale imaging surveys and searches for faint inner solar system objects. We provide a reference implementation via the find-asteroids Python package and this URL: this https URL.

GRB 250702B/EP250702a is an interesting long-duration gamma-ray transient whose nature is in debate. To obtain a full picture in gamma-ray band, we implement a comprehensive targeted search of burst emission in a wide window of 30 days jointly with Insight-HXMT, GECAM and Fermi/GBM data within the ETJASMIN framework. In gamma-ray band, we find there is a 50-second precursor about 25 hours before the 4-hour main burst, which generally consists of 4 emission episodes. Remarkably, we find that the soft X-ray emission (after the main burst) decays as a power-law with start time aligning with the last episode of main emission and index of -5/3 perfectly consistent with the canonical prediction of fallback accretion. We conclude that the properties of precursor, main burst and the following soft X-ray emission strongly support the atypical collapsar Ultra-Long Gamma-Ray Burst (ULGRB) scenario rather than the Tidal Disruption Event (TDE), and all these gamma-ray and soft X-ray emission probably originate from relativistic jet whose luminosity is dominated by the fallback accretion rate during the death collapse of a supergiant star.

The enigma of cosmic ray origin and propagation stands as a key question in particle astrophysics. The precise spatial and spectral measurements of diffuse Galactic gamma-ray emission provide new avenues for unraveling this mystery. Based on 16 years of Fermi-LAT observations, we find that the diffuse gamma-ray spectral shapes are nearly identical for low energies (below a few GeV) but show significant dispersion at high energies (above a few GeV) across the Galactic disk. We further show that the diffuse emission can be decomposed into two components, a universal spectral component dominating at low energies which is consistent with the expectation from interactions of background cosmic rays and the interstellar matter, and a spatially variant component dominating at high energies which is likely due to local accelerators. These findings suggest that there is dual-origin of the Galactic diffuse emission, including the ``cosmic ray sea'' from efficient propagation of particles and the ``cosmic ray islands'' from inefficient propagation of particles, and thus shed new light on the understanding of the propagation models of Galactic cosmic rays.

The Solar Low-Energy X-ray Spectrometer (SoLEXS) on board India's Aditya-L1 mission was launched on 2 September 2023 and commenced solar observations on 13 December 2023 following successful aperture cover deployment. Operating from the Sun-Earth L1 Lagrange point, SoLEXS has been providing continuous Sun-as-a-star soft X-ray spectroscopy across 2-22 keV with 170 eV resolution at 5.9 keV and 1-second temporal cadence since 6 January 2024. The instrument employs two Silicon Drift Detectors with aperture areas of 7.1 mm$^2$ and 0.1 mm$^2$ to accommodate the full dynamic range of solar activity from A-class to X-class flares. This paper presents comprehensive ground and on board calibration procedures that establish SoLEXS's quantitative spectroscopic capabilities. Ground calibration encompassed energy-channel relationships, spectral resolution characterization, instrument response functions, and collimator angular response measurements, with thermo-vacuum testing validating performance stability across operational temperature ranges. On board calibration utilizing an internal $^{55}$Fe source demonstrated preserved post-launch spectral resolution (164.9-171.2 eV), while cross-calibration with GOES-XRS and Chandrayaan-2/XSM confirmed radiometric accuracy and flux agreement. The instrument's 100% observational duty cycle at L1 enables unprecedented continuous monitoring of solar flare evolution across all intensity classes, providing calibrated data for advancing coronal heating mechanisms, flare energetics, and flare-coronal mass ejection relationship studies through soft X-ray spectroscopy.

Accurate estimates of internal red-giant rotation rates are a crucial ingredient for constraining and improving current models of stellar rotation. Asteroseismic rotational inversions are a method to estimate these internal rotation rates. In this work, we focus on the observed differences in the rotationally-induced frequency shifts between prograde and retrograde modes, which were ignored in previous works when estimating internal rotation rates of red giants using inversions. We systematically study the limits of applicability of linear rotational inversions as a function of the evolution on the red-giant branch and the underlying rotation rates. We solve for the oscillation mode frequencies in the presence of rotation in the lowest-order perturbative approach. This enables a description of the differences between prograde and retrograde modes through the coupling of multiple mixed modes. We compute synthetic rotational splittings taking these near-degeneracy effects into account. We use red-giant models with one solar mass, a large frequency separation between 16 and 9 microhertz and core rotation rates between 500 and 1500 nHz covering the regime of observed parameters of Kepler red-giant stars. Finally, we use these synthetic data to quantify the systematic errors of internal rotation rates estimated by means of rotational inversions in the presence of near-degeneracy effects. We show that the systematic errors in the estimated rotation rates introduced by near-degeneracy effects surpass observational uncertainties for more evolved and faster rotating stars. The estimated rotation rates of some of the previously analysed red giants suffer from significant systematic errors that have not been taken into account yet. Notwithstanding, reliable analyses with existing inversion methods are feasible for a number of red giants within the parameter ranges determined here.

Time-delay cosmography, by monitoring the multiply imaged gravitational lenses in the time domain, offers a promising and independent method for measuring cosmological distances. However, in addition to the main deflector that produces the multiple images, the large-scale structure along the line-of-sight (LoS) will also deflect the traveling light rays, known as weak lensing (WL). Due to resolution limitations, accurately measuring WL on arcsecond scales is highly challenging. In this work, we evaluate the LoS effects on both lensing images and time-delay measurements using a more straightforward, high-resolution N-body simulation that provides a more realistic matter distribution compared to the traditional, computationally cheaper halo rendering method. We employ the multi-plane ray tracing technique, which is traditionally utilized to compute WL effects at the arcminute scale, extending its application to the strong lensing regime at the arcsecond scale. We focus on the quadruple-image system and present the following findings: 1. In addition to a constant external convergence, large-scale structures within a region approximately 2 arcminutes in angular size act as external perturbers, inducing inhomogeneous fluctuations on the arcsecond scale; 2. These fluctuations cannot be fully accounted for by external shear alone, necessitating the inclusion of external flexion; 3. While incorporating flexion provides a reasonably good fit to the lensing image, the time-delay distance still exhibits a $6.2$\textperthousand~bias and a $2.5\%$ uncertainty. This underscores the limitations of the single-plane approximation, as time-delay errors accumulate along the LoS.

Dense neutrino systems, which display collectivity mediated by the weak interaction, have deep parallels with mean-field kinetic systems governed by other fundamental forces. We identify analogues in fast flavor conversion (FFC) of some time-honored nonlinear phenomena in plasmas and self-gravitating systems. We focus in particular on nonlinear Landau damping and collisionless equilibria, which are likely important pieces of the unsolved puzzle of neutrino oscillations in core-collapse supernovae and neutron star mergers. Our analysis additionally reveals the previously unexplored phenomenon of flavor-wave synchronization.

Planets orbiting in the habitable zones of white dwarfs have recently been proposed as promising targets for biosignature searches. However, since the white dwarf habitable zone resides at 0.01 - 0.1 AU, planets residing there are subject to tidal heating if they have any orbital eccentricity. Previous work (Barnes & Heller 2013) identified nearby planetary companions as potential roadblocks to habitability of planets around white dwarfs, as such companions could induce secular oscillations in eccentricity for the potentially habitable planet, which could in turn heat a surface ocean and induce a runaway greenhouse for even very low values ($e \sim 10^{-4}$) of the eccentricity of the potentially habitable planet. In this work, we examine the potential for general relativistic orbital precession to protect habitable planets orbiting white dwarfs from such a runaway greenhouse, and demonstrate that for some system architectures, general relativity can be protective for planetary habitability.

Exoplanetary systems with multiple giant planets present an opportunity to understand planet formation, migration processes, and long-term system-wide dynamical interactions. In particular, they provide constraints to distinguish between smooth disk-driven migration or more dynamically excited system evolution pathways. We report the discovery and characterization of a unique multi-planet system hosting three gas giant planets orbiting the post-main sequence star TOI-375. The innermost planet, TOI-375 b, was initially detected by the TESS mission and then confirmed with photometric follow-up observations conducted using MEarth and LCOGT, and radial velocity measurements obtained with FEROS and CHIRON. The radial velocity data revealed the presence of two additional planetary candidates, TOI-375 c and TOI-375 d. We find that TOI-375 b is a hot Jupiter with an orbital period of $9.45469 \pm 0.00002$ days, mass $0.745 \pm 0.053,M_\mathrm{J}$, radius $0.961 \pm 0.043, R_\mathrm{J}$, and eccentricity $0.087 \pm 0.042$. The outer two planets, TOI-375 c and TOI-375 d, are warm-cold and cold Jupiters with orbital periods of $115.5^{+2.0}_{-1.6}$ days and $297.9^{+28.9}_{-18.6}$ days, and minimum masses of $2.11 \pm 0.22, M_\mathrm{J}$ and $1.40 \pm 0.28, M_\mathrm{J}$, respectively. In terms of formation and overall system architecture, the physical properties of TOI-375 b are consistent with the core accretion scenario, while the current configuration of the system could be explained by both disk-driven and high-eccentricity migration scenarios. The discovery of TOI-375 as the first known system hosting three or more fully evolved gas giants, with at least one transiting planet, makes it an excellent candidate for testing formation and migration theories.

Swift J174610.4-290018, a peculiar transient X-ray source originally discovered by the Swift satellite in February 2024 at the onset of its outburst, recently attracted intentional or coincident follow-up X-ray observations using Swift, NuSTAR and Chandra. We have performed a comprehensive analysis of the relevant X-ray data to investigate the spectral and temporal properties of this source between October 2000 and July 2024. Archival Chandra data reveal a plausible additional outburst in 2005, followed by a quiescent state in the next $\sim$19 years. The X-ray spectra in both the quiescent and outburst phases are consistent with a thermal plasma spectrum with relatively high temperatures ($\sim$10 keV) and prominent emission lines from both neutral and highly-ionized iron. A previously proposed low-mass X-ray binary/accretion disk corona scenario for Swift J174610, based on XRISM observations near the peak of the 2024 outburst, is examined against the newly derived X-ray properties and is disfavored, in particular due to its difficulty in explaining the quiescent state spectrum. Instead, we suggest a symbiotic binary/recurrent nova scenario, which gains support from many of the observed X-ray properties of Swift J174610 and a close comparison with the famous Galactic recurrent nova RS Oph. If confirmed, Swift J174610 would represent the first nova detected in the Galactic center, offering new insights into the otherwise elusive population of massive white dwarfs as well as wide binaries in the close vicinity of Sgr A*. Our findings call for multi-wavelength follow-up observations for this highly unusual X-ray source.

Next-generation large-scale structure spectroscopic surveys will probe cosmology at high redshifts $(2.3 < z < 3.5)$, relying on abundant galaxy tracers such as Ly$\alpha$ emitters (LAEs) and Lyman break galaxies (LBGs). Medium-band photometry has emerged as a potential technique for efficiently selecting these high-redshift galaxies. In this work, we present clustering analysis of medium-band selected galaxies at high redshift, utilizing photometric data from the Intermediate Band Imaging Survey (IBIS) and spectroscopic data from the Dark Energy Spectroscopic Instrument (DESI). We interpret the clustering of such samples using both Halo Occupation Distribution (HOD) modeling and a perturbation theory description of large-scale structure. Our modeling indicates that the current target sample is composed from an overlapping mixture of LAEs and LBGs with emission lines. Despite differences in target selection, we find that the clustering properties are consistent with previous studies, with correlation lengths $r_0\simeq 3-4\,h^{-1}$Mpc and a linear bias of $b\sim1.8-2.5$. Finally, we discuss the simulation requirements implied by these measurements and demonstrate that the properties of the samples would make them excellent targets to enhance our understanding of the high-$z$ universe.

Recent results from the Dark Energy Spectroscopic Instrument (DESI) have shown a strong statistical preference for a time-evolving dark energy model over $\Lambda$CDM when combining BAO, CMB, and supernova (SN) data. We investigate the robustness of this conclusion by isolating geometric information in weak lensing measurements from the DES Year 3 survey and combining it with different datasets. We introduce a hyperparameter, $\Omega_{\rm m}^{\rm growth}$, to decouple the growth contribution from the lensing 2-point correlation and thus bypass the possible effect of the $\sigma_8$ tension in our analysis. We then combine with the late-time geometric probes provided by BAO and SN, along with CMB primary data. The preference for evolving dark energy is consistent with the DESI-DR2 findings: when combining BAO, primary CMB, and weak lensing data, the $w_0w_a$CDM is preferred at about the $3\sigma$ significance. However, when we add SN, the result is sensitive to the choice of data: if we leave out $z<0.1$ SN data in the analysis, as a test of the effect of inhomogeneous calibration, we obtain a statistical significance below $2\sigma$ for time evolving dark energy. Indeed, the high-z only SN data \textbf{lowers} the evidence for evolving dark energy in all the data combinations we have examined. This underscores the importance of improved SN samples at low redshift and of alternative data combinations. We show that cosmic shear measurements with LSST Year 1 data will provide comparable power to current SN data. We discuss other low-redshift probes provided by lensing and galaxy clustering to test for evolving dark energy.

Recent JWST/NIRSpec observations have revealed strong methane emission at 3.326 microns in the $\approx$482 K brown dwarf CWISEP J193518.59$-$154620.3 (W1935). Atmospheric modeling suggests the presence of a $\approx$300 K thermal inversion in its upper atmosphere, potentially driven by auroral activity. We present an extension of the retrieved spectra of W1935 with and without inversion spanning 1--20 microns, to identify thermal inversion-sensitive spectral features and explore the origin of the object's peculiar characteristics. Our analysis indicates that atmospheric heating contributes approximately 15% to the bolometric luminosity. The model with inversion predicts an additional similar-strength methane emission feature at 7.7 microns and tentative ammonia emission features in the mid-infrared. Wavelengths beyond $\sim$2 microns are significantly influenced by the inversion, except for the 4.1--5.0 microns CO$_2$ and CO features that originate from atmospheric layers deeper than the region where the inversion occurs. W1935 appears as an outlier in Spitzer/IRAC mid-infrared color-magnitude diagrams (CMDs) based on the $m_{\rm Ch1}-m_{\rm Ch2}$ (IRAC 3.6 microns $-$ 4.5 microns) color, but exhibits average behavior in all other combinations that trace clear sequences. This anomaly is likely due to the Ch2 filter probing vertical mixing-sensitive CO$_2$ and CO features that do not correlate with temperature or spectral type. We find that the thermal inversion tends to produce bluer $m_{\rm Ch1}-m_{\rm Ch2}$ colors, so the overluminous and/or redder position of W1935 in diagrams involving this color cannot be explained by the thermal inversion. This analysis provides insights into the intriguing dispersion of cold brown dwarfs in mid-infrared CMDs and sheds light on their spectral diversity.

The Russian invasion of Ukraine damaged or compromised astronomical facilities and has prompted the displacement of researchers. A plan to restore Ukrainian astronomy, rooted in a deeper integration with the international community, is now being developed.

Despite extensive observational and theoretical efforts, the physical processes responsible for shaping the diversity of accelerated electron spectra observed in solar flares remain poorly understood. We use 2D particle-in-cell (PIC) simulations of magnetized plasmas subject to continuous shear-driven magnetic amplification to investigate whether electron temperature anisotropy instabilities in above-the-loop-top (ALT) regions can account for this diversity. We explore how the resulting spectra depend on key plasma parameters: the initial electron temperature $T_e$ and the initial ratio of electron cyclotron to plasma frequencies, $f_e = \omega_{ce}/\omega_{pe}$. In our simulations, the adiabatic evolution of the plasma generates electron temperature anisotropy with the electron temperature perpendicular to the magnetic field being larger than the parallel temperature. This eventually drives electromagnetic instabilities capable of scattering and accelerating electrons. The simulations consistently produce nonthermal tails in the electron spectra whose hardness increases with the initial value of $f_e$, while depending only weakly on $T_e$. For runs in which $f_e \lesssim 1.2$, the spectra exhibit double power-law shapes with downward (knee-like) breaks, and the electron scattering is dominated by OQES modes. In runs with $f_e\gtrsim 1.5$, PEMZ modes dominate and produce harder double power-law spectra with upward (elbow-like) breaks. Cases that include the $f_e\sim 1.2-1.5$ transition yield nearly single power-laws that end with bump-like breaks. Our results support the role of temperature anisotropy instabilities in accelerating electrons in ALT regions, offering a promising framework to help explain the wide range of nonthermal electron spectra reported in solar flare observations.

The outer Galaxy is characterized by a lower metallicity than regions near the Sun, suggesting differences in the formation and survival of molecules in star-forming regions. To understand chemical evolution across the Milky Way, deriving molecular abundances in star-forming regions in the outer Galaxy is essential for refining models of sub-Solar metallicity environments. We analyzed IRAM 30m observations at 3 and 2 mm toward 35 sources at Galactocentric distances of 9$-$24 kpc, within the "CHEMical complexity in star-forming regions of the outer Galaxy" (CHEMOUT) project. We focused on species with the highest detection rates (i.e., HCN, HCO$^+$, c-C$_3$H$_2$, H$^{13}$CO$^+$, HCO, SO) and searched for trends in column densities, abundances, and line widths with Galactocentric distance. Abundances for H$_2$CO and CH$_3$OH were updated using H$_2$ column densities from new NIKA2 dust maps. Fractional abundances relative to H$_2$ of most species (HCN, HCO$^+$, c-C$_3$H$_2$, HCO, H$_2$CO, CH$_3$OH) scale at most with the elemental carbon abundance ([C/H]) up to $\sim$24 kpc. SO shows a steeper gradient than sulfur abundance ([S/H]), while H$^{13}$CO$^+$ shows a shallower gradient than [$^{13}$C/H]. Gas turbulence, inferred from line widths, decreases with Galactocentric distance, suggesting a more quiescent environment in the outer Galaxy with respect to the inner Galaxy. In the outer Galaxy, the formation efficiency of most molecules, following the parent element availability, is comparable or higher (e.g., for H$^{13}$CO$^+$) than in the local Galaxy, whereas SO forms less efficiently. These results have significant implications for chemical models of the outermost star-forming regions and for understanding molecule formation under lower metallicity conditions.

Artificial Intelligence algorithms are introduced in this work as a tool to predict the performance of new chemical compounds as alternative propellants for electric propulsion, focusing on predicting their ionisation characteristics and fragmentation patterns. The chemical properties and structure of the compounds are encoded using a chemical fingerprint, and the training datasets are extracted from the NIST WebBook. The AI-predicted ionisation energy and minimum appearance energy have a mean relative error of 6.87% and 7.99%, respectively, and a predicted ion mass with a 23.89% relative error. In the cases of full mass spectra due to electron ionisation, the predictions have a cosine similarity of 0.6395 and align with the top 10 most similar mass spectra in 78% of instances within a 30 Da range.

Magnetoconvection at the solar surface governs the dynamics in the upper solar atmosphere and sustains the heliosphere. Properties of this fundamental process are poorly described near the solar poles. Here we report the first out-of-ecliptic remote-sensing observations of the south pole of the Sun from a high-latitude campaign of the Solar Orbiter spacecraft which reveal spatial and temporal evolution of supergranular convective cells. The supergranular cells have spatial scales of 20--40\,Mm. From eight days of observations starting on 2025 March 16, our analysis shows that the magnetic network migrates poleward, on average, at high latitudes (above 60\textdegree), with speeds in the range of 10--20\,m\,s$^{-1}$, depending on the structures being tracked. These results shed light on the buildup of the polar magnetic field that is central to our understanding of the solar cycle and the heliospheric magnetic field.

Charting the Epoch of Reionization demands robust assessments of what drives the production of ionizing photons in high-redshift star-forming galaxies (SFGs), and requires better predictive capabilities from current observations. Using a sample of $N=159$ SFGs at $1<z<8$, observed with deep medium-resolution spectroscopy from the JWST/NIRSpec EXCELS survey, we perform a statistical analysis of their ionizing photon production efficiencies ($\xi_\rm{ion}$). We consider $\xi_\rm{ion}$, measured with Balmer line measurements, in relation to a number of key galaxy properties including; nebular emission line strengths ($W_\lambda(\rm{H\alpha})$ and $W_\lambda$( [OIII])), UV luminosity ($M_\rm{UV}$) and UV slope ($\beta_\rm{UV}$), as well as dust attenuation ($E(B-V)_\rm{neb}$) and redshift. Implementing a Bayesian linear regression methodology, we fit $\xi_\rm{ion}$ against the principal observables while fully marginalising over all measurement uncertainties, mitigating against the impact of outliers and determining the intrinsic scatter. Significant relations between $\xi_\rm{ion}$ and $ W_\lambda(\rm{H\alpha})$, $W_\lambda$([OIII]) and $\beta_\rm{UV}$ are recovered. Moreover, the weak trends with $M_\rm{UV}$ and redshift can be fully explained by the remaining property dependencies. Expanding our analysis to multivariate regression, we determine that $W_\lambda(\rm{H\alpha})$ or $W_\lambda$([OIII]), along with $\beta_\rm{UV}$ and $E(B-V)_\rm{neb}$, are the most important observables for accurately predicting $\xi_\rm{ion,0}$. The latter identifies the most common outliers as SFGs with relatively high $E(B-V)_\rm{neb}\gtrsim0.5$, possibly indicative of obscured star-formation or strong differential attenuation. Combining these properties enable $\xi_\rm{ion,0}$ to be inferred with an accuracy of $\sim0.15\,$dex, with a population intrinsic scatter of $\sigma_\rm{int}\sim0.035\,$dex.

The Universe consists of a variety of objects that formed at different epochs, leading to variations in the formation time which represents the time elapsed from the onset of structure formation until the formation time of a particular object. In this work, we present two approaches to reconstruct and constrain the galaxy formation time $t_f(z)$ using non-parametric reconstruction methods, such as Gaussian Processes (GP) and High-performance Symbolic Regression (SR). Our analysis uses age estimates of 32 old passive galaxies and the Pantheon+ type Ia supernova sample, and considers two different values of the Hubble constant $H_0$ from the SH0ES and Planck Collaborations. When adopting the $\Lambda$CDM model and the GP reconstructions, we find $\left<t_f\right>=0.72_{-0.16}^{+0.14}$ Gyr (SH0ES) and $\left<t_f\right>=1.26_{-0.11}^{+0.10}$ Gyr (Planck). Without considering a specific cosmological model, we obtain $\left<t_f\right>=0.71 \pm {0.19}$ Gyr (SH0ES) and $\left<t_f\right> = 1.35_{-0.23}^{+0.21}$ Gyr (Planck). Similar values are obtained from the SR reconstructions, with both methods (GP and SR) indicating the same behavior regarding the time evolution of $t_f(z)$. The results also show significant differences in the formation time from SH0ES and Planck values, highlighting the impact of the $H_0$ tension on the cosmological estimates of $t_f(z)$. In particular, the different approaches used in the analysis agree with each other, demonstrating the robustness and consistency of our results. Overall, this study suggests that galaxies have different evolutionary timescales and that $t_f$ is not constant, with noticeable variations at lower redshifts ($z \lesssim 0.5$).

Recent disk observations have revealed multiple indirect signatures of forming gas giant planets, but high-contrast imaging has rarely confirmed the presence of the suspected perturbers. Here, we exploit a unique opportunity provided by the background star AS209bkg, which shines through a wide annular gap in the AS209 disk, to perform transmission spectrophotometry and directly measure the extinction from gap material for the first time. By combining new VLT/SPHERE and JWST/NIRCam observations with archival HST data from 2005, we model the spectral energy distribution (SED) of AS209bkg over a 19-year baseline. We find that the SED and its variability are best explained by increasing extinction along the line of sight as AS209bkg approaches the gap edge in projection. The extinction is best described by a combination of ISM-like extinction component and a grey extinction component. This points to the presence of grains in the disk outer gap that are larger than in the ISM. We find that the extinction in the gap at $\lambda\sim4.0~\mu$m is $A_{4\,\mu\mathrm{m}} = 2.7^{+0.7}_{-0.7}$ mag, while at H$\alpha$ ($\lambda=0.656~\mu$m), where most searches for accretion signatures take place, the extinction could be as high as $A_\mathrm{H\alpha} = 4.2^{+0.9}_{-1.2}$ mag ($A_V=4.6^{+1.0}_{-1.3}$ mag). This suggests that even wide, deep gaps can significantly obscure emission from protoplanets, even those following a hot-start evolutionary model. Our extinction measurements help reconcile the discrepancy between ALMA-based predictions of planet-disk interactions and the non-detections from sensitive optical and near-infrared imaging campaigns.

High-redshift (z > 2) massive quiescent (MQ) galaxies provide an opportunity to probe the key physical processes driving the fuelling and quenching of star formation in the early Universe. Observational evidence suggests a possible evolutionary link between MQs and dusty star-forming galaxies (DSFGs; or submillimetre galaxies), another extreme high-redshift population. However, galaxy formation models have historically struggled to reproduce these populations - especially simultaneously - limiting our understanding of their formation and connection, particularly in light of recent JWST findings. In previous work, we presented a re-calibrated version of the L-Galaxies semi-analytic model that provides an improved match to observationally-inferred number densities of both DSFG and MQ populations. In this work, we use this new model to investigate the progenitors of MQs at z > 2 and the physical mechanisms that lead to their quenching. We find that most MQs at z > 2 were sub-millimetre-bright ($S_{870}$ > 1 mJy) at some point in their cosmic past. The stellar mass of MQs is strongly correlated with the maximum submillimetre flux density attained over their history, and this relation appears to be independent of redshift. However, only a minority of high-redshift DSFGs evolve into MQs by z = 2. The key distinction between typical DSFGs and MQ progenitors lies in their merger histories: MQ progenitors experience an early major merger that triggers a brief, intense starburst and rapid black hole growth, depleting their cold gas reservoirs. In our model, AGN feedback subsequently prevents further gas cooling, resulting in quenching. In contrast, the broader DSFG population remains sub-millimetre-bright, with star formation proceeding primarily via secular processes, becoming quenched later.

Along the last ten years, a general relativistic method has been developed to generate analytical expressions for the black hole (BH) parameters in terms of observations, namely the frequency shift of photons emitted by orbiting test particles and their positions on the sky. Applications of the method to astrophysical systems such as Active Galactic Nuclei (AGNs), in particular to megamaser systems orbiting the central BH on their flat accretion disks, showed a coupling behavior in the mass-to-distance ratio $M/D$. Estimates for the ratio $M/D$ of a sample of BHs hosted at the core of several AGNs have been performed in recent years with the help of this method. However, both analytical expressions and statistical estimations depend only on the $M/D$ ratio rather than on independent parameters. It is of current general interest to work with decoupled parameters in order to safeguard the intrinsic physical information encoded in each of them, given their high scientific relevance in understanding the structure of our Universe. The purpose of this work is to find analytical expressions for the mass and distance of a Schwarzschild BH in terms of astrophysical observations by introducing a slight warping in the accretion disk of the orbiting megamasers. As a result, independent analytical formulas for the mass and distance of AGN supermassive BHs are presented in terms of astrophysical observations: maser frequency shifts, disk parameters, and the galaxy's peculiar redshift.

We study ultralight scalar fields with quadratic couplings to Standard-Model fermions and derive strong constraints from white-dwarf mass-radius data. Such couplings source scalar profiles inside compact stars, shift fermion masses, and can produce a new ground state of matter. We analyze couplings to electrons and to nucleons, incorporating composition and finite-temperature effects in white dwarf structure and equations of state. We identify two robust observables: (i) forbidden gaps - ranges of radii with no stable configurations - and (ii) characteristic shape distortions that drive white dwarf masses toward the Chandrasekhar limit (electron couplings) or shift the maximum mass (nucleon couplings). Confronting these predictions with precise measurements for Sirius B and Procyon B, together with the global white dwarf population, excludes large regions of unexplored parameter space and extends earlier QCD-axion-specific bounds to a broader class of scalar theories. Our stellar constraints rely only on sourcing and do not assume the scalar constitutes dark matter; where mass reductions are small, precision laboratory searches remain competitive. White-dwarf astrophysics thus provides a powerful, largely assumption-minimal probe of ultralight, quadratically coupled scalars.

We point out that ultralight scalar dark matter that modulates neutrino masses can be significantly thermal damped by cosmic neutrinos in the early universe. This dissipative effect arises as a backreaction from the neutrinos which are being driven slightly out of thermal equilibrium by the scalar. We estimate the rate of such thermal damping and explore its phenomenological implications. For a scalar that is produced early, we find that the effect of thermal damping results in a predictable final abundance largely insensitive to its initial condition while circumventing late time limits. This motivates a parameter-space line to target experimentally.

We uncover a universal sector of relativistic fluid dynamics by taking a novel ultrarelativistic limit in which the temperature tends to zero while the flow simultaneously approaches the speed of light. In this regime, hydrodynamics becomes an effective theory of \emph{null matter}, characterised by a preferred null vector, a preferred scale, and their gradients. We show that this theory of null matter constitutes an example of a hydrodynamic theory that can be linearly stable and causal in an arbitrary choice of frame. The framework developed here for null matter can offer insights into ultrarelativistic heavy-ion collisions, astrophysical phenomena with inherently large Lorentz factors, and the dynamics of black hole horizons.

Injecting 1-13.6 eV photons into the early universe can suppress the molecular hydrogen abundance and alter the star formation history dramatically enough to produce direct collapse black holes. These, in turn, could explain the recently observed population of puzzling high-redshift supermassive black holes that appear to require super-Eddington accretion. We show that axion dark matter decay in the intergalactic medium can account for this energy injection. We use a single zone model of the gas core and semi-analytically evolve its chemo-thermal properties to track the conditions for which the system becomes an atomic cooling halo-a necessary precursor for the production of heavy black hole seeds to explain the high-redshift black hole population. Windows of axions masses between 24.5-26.5 eV with photon couplings as low as $4\times 10^{-12}$/GeV may realize this atomic cooling halo condition. We highlight the significance of the band structure of molecular hydrogen on the effectiveness of this process and discuss estimates of the heavy seed population and prospects for testing this model.

Evolution of cosmic domain walls (DWs) settles to the scaling solution, which is often assumed to be independent of initial conditions. However, lattice simulations performed in this work reveal a clear dependence of the scaling DW area on the initial configuration of the sourcing scalar field, specifically, its infrared (IR) properties. Namely, the DW area grows as one suppresses IR modes in the initial scalar field spectrum. This growth is saturated, when the area parameter $\xi$ commonly used in the literature reaches the value $\xi_{max} \approx 1.2$. The dependence of $\xi$ on IR modes is argued to be of non-physical origin: it is likely to be due to effects of the lattice boundary. Assuming that physically the memory of initial conditions is erased, one recognizes $\xi \approx 1.2$ obtained in the situation with maximally suppressed IR modes as a genuine universal value of the area parameter in the scaling regime. We demonstrate that ignorance about initial conditions may affect predictions for the energy density of gravitational waves by the factor five. The spectral shape of gravitational waves is also affected by the choice of initial conditions, most notably in the low-frequency part. Likewise, we revisit annihilation of DWs under the influence of a potential bias. It has been previously found in Ref. [19] that the annihilation happens significantly earlier compared to the estimate based on the simple balance between the potential bias and surface energy density. We further support this observation and show that the tendency towards an earlier annihilation gets even stronger upon removing IR modes in simulations.

Dual-comb spectroscopy (DCS) utilizes a pair of broadband mutually coherent laser frequency combs to enable high-resolution, high-accuracy spectroscopic measurements with atomic-clock-level frequency referencing, and rapid, multiplexed acquisition without moving parts. It has traditionally been confined to specific domains: terahertz, infrared, visible, and ultraviolet, each requiring distinct comb sources and detection mechanisms tailored to the nature of the spectroscopic target. Yet, similar techniques may be implemented in the terahertz (THz) and mid-infrared (MIR) regions, such as optical rectification for comb generation and electro-optic sampling for detection, both using crystals with quadratic nonlinearity. However, in the Reststrahlen band near phonon resonances in these crystals, typically between 5 and 10 THz, both linear and nonlinear susceptibilities experience abnormally high dispersion, and light propagation is strongly suppressed. This confines DCS operation to spectral regions either below or above the Reststrahlen band and effectively separating the THz and MIR domains. Here we demonstrate high-resolution DCS performed simultaneously over two broad spectral bands, each spanning an octave or more. The measurements cover both the MIR (350-1150 cm$^{-1}$; 8.7-28.5 $\mu$m; 10.5-34.5 THz) and the THz region (80-160 cm$^{-1}$; 62.5-125 $\mu$m; 2.4-4.8 THz), effectively bridging these traditionally separate regions within a single acquisition. This enables direct cross-referencing of molecular absorption line strengths across widely separated spectral domains. As a proof of concept, we demonstrate the simultaneous acquisition of ro-vibrational and pure rotational absorption spectra of ammonia (NH$_3$) with a spectral resolution of 7.3 MHz (0.00024 cm$^{-1}$), sufficient to fully resolve Doppler-broadened line shapes across the entire measured spectral range.

We present a new analysis on sterile neutrino cosmologies using the Dark Energy Spectroscopic Instrument (DESI) second data release (DR2) baryon acoustic oscillation (BAO) measurements in combination with cosmic microwave background (CMB), CMB lensing, and supernova data. We show that BAO observables are intrinsically less sensitive to the combined effects of relativistic energy density, $N_{\rm eff}$, and the sum of neutrino masses, $\Sigma m_\nu$, which are both augmented in sterile neutrino cosmologies. With SH0ES local expansion rate, $H_0$, data, we find $N_{\rm eff} = 3.43 \pm 0.13$, reducing the Hubble tension to $2.4\sigma$. For a 0.1~eV sterile neutrino, we find $N_{\rm eff}=3.50$ as the best fit. For this representative $N_{\rm eff}$, we find an upper limit of $m_s < 0.17$ eV (95\% CL), greater than a factor of four weaker than standard constraints on $\Sigma m_\nu$. When SH0ES is included, light sterile neutrinos with masses $m_s\simeq0.1$--$0.2$ eV are favored at $\gtrsim 3\sigma$, whereas eV-scale sterile masses remain strongly excluded by the data in the cosmologies we study. Our findings confirm our previous results that partially thermalized sub-eV sterile neutrinos are preferred by the SH0ES $H_0$ data. The preferred $m_s$ mass scale overlaps with, but is not identical to, that favored in neutrino oscillation solutions to short-baseline anomalies.

Gravitational wave (GW) experiments have transformed our understanding of the Universe by enabling direct observations of compact object mergers and other astrophysical phenomena. This chapter reviews the concepts of GW detectors, such as LIGO, Virgo, and KAGRA, and describes their operating principles, data acquisition and analysis techniques, and some of the methods used to extract source properties. The scientific impact of GW observations is discussed as well, including contributions to astrophysics, tests of general relativity, and cosmology. We also examine the role of multimessenger astronomy and the complementarity between different GW detectors and with other astroparticle experiments. Finally, we outline future prospects with next-generation detectors, like the Einstein Telescope and Cosmic Explorer, and space-based missions.

We investigate the tidal disruption of a neutron star (NS) near a black hole (BH), and for the first time, to the best of our knowledge, near a naked singularity (NaS). For a BH with a mass greater than about $10 M_{\odot}$, the tidal disruption of NS should occur within the event horizon, and hence neither can the stellar material escape nor a distant observer observe the disruption. Since NaS does not have an event horizon, a significant portion of the NS's material can escape, and the tidal disruption can be observed by a distant observer. One could identify such an event from the observed emission from the disrupted NS's material and the decay of the light curve of the disruption event. The escape of a significant fraction of the NS's material may also have implications for the heavy elements in the universe. Moreover, observing such an event can be useful for confirming a NaS, probing its spacetime, and studying the motion of matter in such a geometry. This may help constrain the NS parameters and equation of state models. As a first step in this direction, we calculate here the tidal disruption radius and other parameters for a specific type (Joshi-Malafarina-Narayan type 1) of NaS and compare our results with observations.

Software code generation using Large Language Models (LLMs) is one of the most successful applications of modern artificial intelligence. Foundational models are very effective for popular frameworks that benefit from documentation, examples, and strong community support. In contrast, specialized scientific libraries often lack these resources and may expose unstable APIs under active development, making it difficult for models trained on limited or outdated data. We address these issues for the Gammapy library by developing an agent capable of writing, executing, and validating code in a controlled environment. We present a minimal web demo and an accompanying benchmarking suite. This contribution summarizes the design, reports our current status, and outlines next steps.

Hypernuclei and hypernuclear matter connect nuclear structure in the strangeness sector with the astrophysics of neutron stars, where hyperons are expected to emerge at high densities and affect key astrophysical observables. We present the first {\em ab initio} calculations that simultaneously describe single- and double-$\Lambda$ hypernuclei from the light to medium-mass range, the equation of state for $\beta$-stable hypernuclear matter, and neutron star properties. Despite the formidable complexity of quantum Monte Carlo~(QMC) simulations with multiple baryonic degrees of freedom, by combining nuclear lattice effective field theory with a newly developed auxiliary-field QMC algorithm we achieve the first sign-problem free {\em ab initio} QMC simulations of hypernuclear systems containing an arbitrary number of neutrons, protons, and $\Lambda$ hyperons, including all relevant two- and three-body interactions. This eliminates reliance on the symmetry-energy approximation, long used to interpolate between symmetric nuclear matter and pure neutron matter. Our unified calculations reproduce hyperon separation energies, yield a neutron star maximum mass consistent with observations, predict tidal deformabilities compatible with gravitational-wave measurements, and give a trace anomaly in line with Bayesian constraints. By bridging the physics of finite hypernuclei and infinite hypernuclear matter within a single {\em ab initio} framework, this work establishes a direct microscopic link between hypernuclear structure, dense matter composition, and the astrophysical properties of neutron stars.

Numerical relativity simulations provide a means by which to study the evolution and end point of strong over-densities in cosmological spacetimes. Specific applications include studies of primordial black hole formation and the robustness of inflation. Here we adopt a toy model previously used in asymptotically flat spacetimes to show that, for given values of the over-density and the mean curvature, solutions to the Hamiltonian constraint need not exist, and if they do exist they are not unique. Specifically, pairs of solutions exist on two branches, corresponding to strong-field and weak-field solutions, that join at a maximum beyond which solutions cease to exist. As a result, there is a limit to the extent to which an over-density can be balanced by intrinsic rather than extrinsic curvature on the initial slice. Even below this limit, iterative methods to construct initial data may converge to solutions on either one of the two branches, depending on the starting guess, leading to potentially inconsistent physical results in the evolution.