Papers for Wednesday, Mar 11 2026

With JWST, we are directly imaging cold (~200-300K), solar-age giant exoplanets for the first time. At these temperatures many molecular features appear and water-ice clouds may condense and affect the emission spectrum; early photometric measurements of cold giant planets are already showing some tension with the predictions of cloud-free, solar-metallicity atmosphere models. Here we present new JWST/MIRI coronagraphic observations of the cold giant exoplanet Eps Ind Ab at 11.3um. Together with archival data, we use these new observations to study the atmosphere of this cold exoplanet, and we also re-fit its orbit, finding an updated mass of $7.6\pm0.7$ Mj and an eccentricity of $0.24^{+0.11}_{-0.08}$. The planet is significantly brighter (by $0.88\pm0.08$ mag) at 11.3um than at 10.6um, indicating the presence of ammonia. However, this ammonia feature is shallower than expected. This could indicate a low-metallicity or nitrogen-depleted atmosphere, but our preferred explanation is the presence of thick water-ice clouds that suppress the ammonia feature and the near-IR emission of Eps Ind Ab. Photometry of the small but growing sample of cold, giant exoplanets demonstrates that they are consistently fainter than expected between 3 to 5um, consistent with the water-ice cloud hypothesis. 10.6um and 11.3um photometry of this cold exoplanet sample would be valuable to determine whether the suppressed ammonia feature is universal, and to frame a new open question about the underlying physical cause.

The ongoing observations from ground based gravitational-wave observatories have led to the detection of more than a hundred merger events between black holes. We use the LIGO-Virgo-KAGRA (LVK) observations from 2015 to early 2024, to test the population synthesis of these merging binaries; which will allow us to probe the formation mechanisms and environments of these black holes. We test if the current sample of binary black holes can be explained only by the merger of black holes coming from the collapse of the cores of massive stars, i.e. as just first generation black holes merging with each other. Those black holes' masses will roughly follow a power-law distribution. We also test if in addition to the merger between first generation black holes, there is evidence for a second population of black hole binaries in which at least one the binaries' members is the product of an earlier merger between black holes. These binaries are typically referred to as signals of hierarchical mergers. Such a population can possibly explain the observation of very massive black hole binaries by the LVK collaboration. We find that the LVK observations give a statistical preference in log-likelihood of up to $- 2 \Delta ln\mathcal{L} = -150$ or in log-Bayes factor of up to $ln\textrm{BF} = 71$, for the full sample of black hole binaries originating from a combination of black holes following a power-law distribution and black holes from hierarchical mergers. The ratio of black holes following a power-law mass-distribution to a mass-distribution expected from hierarchical mergers is found to be as high as one-to-one. We also consider that some of the LVK black hole merging binaries are the result of primordial black holes (PBHs), merging inside dark matter halos and in the intergalactic medium. Adding a third population is preferred. [abridged]

The recent pericentric passage of the Large Magellanic Cloud (LMC) through the Milky Way (MW) has dislodged its centre of mass, inducing a state of dynamical disequilibrium, the reflex motion, in the kinematics of outer stellar halo stars. Using data out to distances of $160 \, \rm kpc$ from the combined H3+SEGUE+MagE outer halo survey, we constrain the mass of the MW and LMC, as well as the resulting reflex motion and the velocity anisotropy of the stellar halo. Using a suite of 32,000 rigid MW--LMC simulations, each with a MW stellar halo evolved to the present day in the combined MW--LMC potential, we perform Simulation Based Inference by training a neural posterior estimator on the means and dispersions of the radial and tangential velocities of stars from the combined H3+SEGUE+MagE outer halo sample. Relative to halo stars at $100 \, \rm kpc$, we find the magnitude of the reflex velocity to be $v_{\rm travel} = 39.4^{+7.6}_{-7.2}\,\rm km \, s^{-1}$. Simultaneously, we determine the enclosed MW mass to be $M_{\rm MW}(< 50 \, \rm kpc) = 3.63 \pm 0.16 \times 10^{11}\, \rm M_{\odot}$ and the enclosed LMC mass to be $M_{\rm LMC}(< 50 \, \rm kpc) = 9.74^{+2.07}_{-1.81} \times 10^{10}\, \rm M_{\odot}$. Our results suggest that the total LMC mass must be at least $\sim20\%$ that of the MW. The velocity anisotropy prior to the LMC's infall is constrained to be $\beta_0 = 0.61 \pm 0.03$. Finally, we demonstrate that failing to account for the LMC in models biases the MW mass estimate to prefer slightly more massive values.

We predict the gamma-ray line emission from $r$-process nuclei synthesized in the ejecta of the accretion-induced collapse (AIC) of a magnetized, rapidly rotating white dwarf. Using ejecta from a two-dimensional general-relativistic neutrino-magnetohydrodynamic simulation, further evolved with a radiation-hydrodynamics code coupled to an in-situ nuclear reaction network, we construct angle-dependent gamma-ray spectra in the $0.01$-$10\,\mathrm{MeV}$ band via composition-dependent ray-tracing through the ejecta. The emission between $\sim$1 and $10\,$d is dominated by $^{132}$I ($t_{1/2} = 2.3\,$h), continuously replenished by the decay of its parent $^{132}$Te ($t_{1/2} = 3.2\,$d), with additional contributions from $^{131}$I, $^{133}$Xe, and $^{132}$Te. At $t\gtrsim 20$ d, $^{56}$Co (from $^{56}$Ni decay) becomes the primary emitter. The simultaneous presence of $r$-process and iron-peak gamma-ray lines is distinctive of AIC ejecta and absent in binary neutron star mergers, where iron-peak nuclei are generally not synthesized. Comparing with the $3\sigma$ continuum sensitivities of planned MeV gamma-ray telescopes (COSI, AMEGO-X, e-ASTROGAM, GRAMS, GammaTPC), we find the brightest $r$-process lines detectable to $\sim 10\,\mathrm{Mpc}$ by GammaTPC and GRAMS, with the signal approaching their sensitivity threshold at $30\,\mathrm{Mpc}$. The $r$-process spectral features survive time integration over $\sim 30$ d exposures, demonstrating robustness against the long observation times required by gamma-ray detectors.

Low-mass stars from the first epoch of star formation may still persist in the Milky Way and its satellite dwarf galaxies today; however, their detection is confounded by surface pollution from interstellar accretion and internal mixing, which obscure their primordial composition and blur their distinction from second-generation stars. Asteroseismology offers a probe of the internal structure and evolutionary state of stars, and hence may aid in the search for primordial stars. In this second paper of the series, we present the first non-radial adiabatic pulsation analysis of low-mass, metal-free stellar models. We use a $0.85\,M_\odot$ red giant as a case study and compare its seismic signatures with those of higher-metallicity models. At the same central hydrogen fractions, Pop III main-sequence models display systematically higher $r_{02}\equiv\delta\nu_{02}/\Delta\nu$ ratio and lower $\Delta\nu$ than metal-enriched analogues, a direct consequence of their larger internal sound speeds and steeper core-envelope stratification. To interpret the structural dependence during giant evolution, we introduce a composite asteroseismic diagnostic, $\psi\equiv\Delta\nu/\Delta\Pi_1$, which traces how metallicity influences the balance between acoustic and buoyancy cavities through its imprint on opacity, core contraction, and mean molecular-weight gradients. Pop III models occupy a distinct locus in the $\psi-\Delta\Pi_1$ plane due to their radiative interiors with lower mean densities and delayed development of core mean molecular weight gradients. We find that asteroseismology is a powerful diagnostic for identifying relic Pop III stars despite potentially polluted surfaces, providing a clear pathway for future searches of the Galaxy's oldest surviving stars with upcoming surveys.

Axions and axion-like particles (ALPs) arise naturally in many extensions of the Standard Model and are among the well-motivated candidates for dark matter. In the presence of magnetic fields of galaxy clusters, Cosmic Microwave Background (CMB) photons can convert to ALPs, with the efficiency of the process governed by the cluster electron density and magnetic field profiles, the photon--ALP coupling strength ($g_{a\gamma}$), as well as the frequency ($\nu$) of the photon at the redshift of the cluster. The CMB blackbody spectrum suggests that this resonant conversion also takes place at radio wavelengths, following the spectral behaviour of the ALP distortion signal. This opens a new window to search for ALPs using cosmic variance cancellation (CVC), with multi-frequency tracers of the same phenomenon in CMB photon--ALP resonant conversion. The constraints on the ALP signal ratios from different combinations of microwave and radio bands of the Simons Observatory (SO) and the Square Kilometre Array (SKA) can be significantly improved using CVC compared to the case of using auto-only spectra from the two experiments. With the large number of galaxy clusters that will be observed by SO and SKA, we will be able to obtain much more information using CVC, especially for low-mass ALPs with stronger signals. Using the auto-only spectra from galaxy clusters up to redshift $z = 1$ for inference of the normalized ratio parameter, we obtain a standard deviation of $5.9 \times 10^{-2}$ for an ALP mass $m_a = 10^{-14} \, \mathrm{eV}$, which improves to $1 \times 10^{-2}$ using CVC. This method provides a universal probe of the ALP distortion signal using its spectral dependence and can also invalidate false detections of the ALP signal based on its frequency behaviour in different bands.

Luminous quasars at $z > 6$ are key probes of early supermassive black hole (SMBH) growth, massive galaxy evolution, and intergalactic medium properties during cosmic reionization. However, their discovery is very challenging due to their scarcity and overwhelming contamination, as foreground ultracool dwarfs (UCDs) outnumber $z>6$ quasars by 2-4 orders of magnitude. In this work, we leverage the extensive coverage of DESI Legacy Survey DR10 to conduct a self-supervised search for quasars at $z > 6$, directly analyzing multiband optical images and minimizing the biases of traditional catalog-driven color-color selection criteria. By applying a contrastive learning (CL) method followed by spectral energy distribution (SED) fitting prioritization, we identified 1139 high-priority quasar candidates, for which we expect a competitive $\sim$1:1 quasar-to-UCD ratio based on literature samples. We spectroscopically confirm 16 new quasars at $z = 5.94$-6.45, achieving a 45\% success rate. Remarkably, all 16 objects are relatively bright ($M_{1450} < -25.5$) quasars, including several with unusual properties such as narrow Ly$\alpha$ emission (FWHM $< 2600$ km s$^{-1}$), strong Ly$\alpha$+NV emission with equivalent width $>100$ Å, and mildly red observed-frame near-infrared (NIR) continua ($z - J > 0.4$). Notably, three of them would have been missed by traditional color-color selections. These results highlight the power of self-supervised machine learning combined with SED fitting prioritization to uncover rare distant sources beyond conventional techniques. Our approach offers a scalable and robust framework for data mining and can be readily extended to forthcoming wide-field surveys such as Rubin/LSST, 4MOST, Euclid, and Roman, improving the census of high-redshift quasars and constraints on SMBH formation and evolution in the first billion years of the Universe.

The magnetorotational collapse of massive stars copiously emits neutrinos of all flavors, with a prominent hierarchy between the non-electron and electron flavor average energies. Relying on a three-dimensional neutrino-magnetohydrodynamic simulation of a $13 M_\odot$ progenitor, we investigate flavor conversion in matter. We find that, in addition to resonant flavor conversion of neutrinos and antineutrinos in matter, (anti)neutrinos experience chirality-flipping interactions due to their non-zero magnetic moment ($\mu \lesssim 10^{-12} \mu_B$) and large magnetic field in the source ($B \simeq 10^{15}$ G). For Majorana neutrinos, this leads to resonant flavor-changing neutrino-antineutrino mixing. The event rate expected from a Galactic collapse at current and next-generation neutrino telescopes, such as IceCube and Hyper-Kamiokande, strongly depends on the orientation of the magnetorotational collapse with respect to the observer direction and flavor conversion scenario. The event rate is expected to be larger for an observer facing head on the jet launched during the stellar collapse and peaks around $400$-$600$ ms after bounce. Our work highlights that understanding the rich phenomenology of flavor conversion in magnetorotational collapses is essential to take full advantage of the joint detection of neutrinos and gravitational waves from these sources.

Recent improvements to stellar atmospheric models have merited updated flux calibration for high priority STIS observing modes. Specifically, in the FUV and NUV, continuum differences of 1-3% are present between the newest models (CALSPECv11) and previous models (CALSPECv04-v07). As a result of these improvements the STIS team has derived updated sensitivity curves and blaze shift coefficients for a variety of echelle modes in order to meet targeted flux accuracies. The first series of echelle sensitivity updates primarily targeted post-Servicing Mission 4 (SM4; in 2009) observations. In this ISR, we investigate instead applying a simple scaling (derived from the ratio of new vs old CALSPEC model continua) to the previously determined throughputs of STIS echelle modes. This alternative approach has a straightforward implementation and provides reasonable accuracy, especially in cases where available calibration data are lacking (e.g., pre-SM4 era). Adopting this scaling approach, we delivered pre-SM4 throughput updates for 8 echelle modes, resulting in typical improvements of 0.5-2.4% across the FUV and NUV.

The STIS echelle gratings can be used with a variety of different central wavelength settings. "Secondary" wavelength settings, designed to cover select absorption or emission lines, have not been calibrated as precisely as their primary mode counterparts. In particular, secondary echelle mode traces (and subsequent extraction regions) have been previously defined using straight line fits to each spectral order. In this work, we define a new general method for defining echelle traces that utilizes Gaussian process regression and accounts for the detailed curvature of each order across the detector. Across a variety of echelle grating and central wavelength settings, we find that this method can improve flux throughput by $\sim4\%$ especially near wavelengths located close to the edge of the detector. We have used this method to provide new traces and update reference files for 9 different echelle modes for both pre- and post-Servicing Mission 4 (SM4; in 2009) observations.

Gamma-ray bursts (GRBs) are extremely powerful stellar explosions that have been observed to huge distances with redshifts exceeding 9. Although GRBs are not standard candles, one may standardize them by calibrating certain correlations that link an intrinsic parameter to an observed one. Two such correlations that have been discovered are the Amati relation and the Yonetoku relation. In this paper, we compile a large sample of 241 Swift long GRBs for the purpose of examining whether the Amati and Yonetoku relations are immune to redshift evolution. Our methodology encompasses two approaches: the first involves binning the data by redshift and fitting the two relations for each bin, then checking whether the fitting parameters evolve with redshift; the second approach involves using a redshift cutoff to divide the data into a low-redshift group and a high-redshift group, then checking whether the fitting parameters for the two relations are consistent with one another. Our results indicate that the Amati and Yonetoku relations are robust in the sense that they do not show any systematic or significant redshift evolution. Moreover, our results indicate that the high redshift bins show better fits compared to the low redshift bins, which indicates that the Amati and Yonetoku relations are more reliable for high redshift and hence are promising cosmological probes.

We present a broadband spectral analysis of the black hole X-ray binary GX 339-4 during its 2021 outburst, covering both hard and soft spectral states. Using simultaneous observations from NuSTAR, NICER, and Insight-HXMT, we investigate the evolution of the accretion disk with a focus on the disk normalization derived from the diskbb component, which serves as a proxy for the apparent inner disk radius. In the standard single Comptonization model, the disk normalization in the hard state is more than an order of magnitude lower than in the soft state ($\sim$0.3$\times$10$^3$ vs. $\sim$3.0$\times$10$^3$). This result contradicts the widely accepted view that the disk radius is smaller in the soft state than in the hard state. By incorporating an additional warm Comptonization component, the disk normalization in the hard state increases to values ($\gtrsim 10^4$) exceeding those in the soft state ($\sim 10^3$), yielding results consistent with a physically truncated, cooler accretion disk. The results of this work support the presence of a dual-corona geometry in the hard state, comprising both a hot, optically thin corona and a warm, optically thick corona, while the soft state spectrum is well described by a single hot Comptonization component alone. Our findings emphasize the importance of including a warm corona in hard-state spectra, as it leads to a more physically consistent picture of the accretion geometry across spectral states.

Understanding the formation and evolution of the Milky Way (MW) requires detailed knowledge of its satellite galaxies. In this study, we focus on the Sextans dwarf spheroidal (dSph) galaxy, a faint, dark matter (DM)-dominated satellite, to investigate the role of tidal and baryonic effects in shaping its observed properties. Using tailored $N$-body simulations, we explore possible orbits of Sextans in different MW models to reconstruct its progenitor's properties. Our simulations demonstrate the stars in Sextans are only mildly affected by galactic tides and the stellar kinematics provide robust constraints on its dynamical mass within the half-light radius, while the tidal mass loss of its DM component depends primarily on MW mass. The recovered infall mass of Sextans ranges from $1.22$ to $3.14\times10^9\rm\,M_\odot$ for MW masses from $0.8$ to $2\times10^{12}\rm\,M_\odot$. If the DM density remained as cuspy as NFW profile, the infall mass would be smaller by a factor of 2. Although with large ranges, the possible infall masses of Sextans recovered by our simulations are consistent with the stellar mass-halo mass relation in TNG50 and abundance matching results. We find some cases for the cuspy DM density profile where the infall mass is smaller than $10^9\rm\,M_\odot$, possibly indicating that star formation in Sextans is more efficient than in other satellites. The recovered DM halo structural parameters from our simulations provide valuable constraints for future studies on the DM content and formation history of Sextans.

Low-metallicity massive stars are assumed to be progenitors of certain supernovae, gamma-ray bursts, and gravitational wave emitting mergers. These exotic phenomena contribute to their host galaxies through strong ionizing radiation and mechanical feedback. Here we investigate a certain type of very metal-poor (0.02 Zsun) hot massive single stars that rotate fast and evolve chemically homogeneously. Combining state-of-the-art theories of stellar evolution and stellar atmospheres modelling we predict synthetic spectra of these stars corresponding to different masses and evolutionary phases. The predicted spectra in early evolutionary phases is classified mainly as an early-O type giant or supergiant while in later evolutionary phases most of our model spectra are assigned to the WO-type spectral class. The Hubble Space Telescope's (HST) Ultraviolet Legacy Library of Young Stars as Essential Standards (ULLYSES) program will enable us to compare our predicted spectra with observations of stars of similar nature (e.g., metal-poor stars in Sextant A).

A well-established method exists for predicting the detectability of solar-like oscillations and has been widely used to support target selection for space-based photometric missions. The method evaluates the probability of an asteroseismic detection from the expected global signal-to-noise ratio (SNR) of the oscillation signal relative to the broadband background from shot noise and granulation. Stellar parameters are used to estimate the oscillation and granulation signals, while instrumental properties and apparent stellar brightness determine the expected shot noise. We investigate whether there is an optimal choice for the frequency range, $W$, over which the global SNR is calculated. The oscillation power is assumed to follow a Gaussian-like envelope with full width at half maximum $\Gamma_{\rm env}$ centred on the frequency of maximum oscillation power. It has commonly been assumed that $W \simeq 2\Gamma_{\rm env}$ when predicting detections. We compute numerical predictions of the global SNR and corresponding detection probabilities for a range of stellar and observational parameters, adopting widths $W=\alpha\Gamma_{\rm env}$ where $\alpha$ is a multiplicative factor. We also examine the impact of this choice on detection yields across a population of targets using bright solar-like oscillators observed by TESS as a representative sample. We find that the commonly adopted value $\alpha \simeq 2$ is suboptimal and that $\alpha \simeq 1.2$ maximises the detection probability. This choice can also significantly affect predicted detection yields for stellar samples. We therefore recommend adopting $W \simeq 1.2\Gamma_{\rm env}$ both when computing detection probabilities and when searching for oscillations in real data via tests of excess mode power, as it optimises the probability of robust detections.

We present astrometric measurements for 13 cold brown dwarfs in the solar neighborhood (d < 20pc). By combining archival Spitzer data with our own Hubble Space Telescope (HST) observations, we achieve parallax uncertainties typically around 10%. Using Spitzer and HST photometry we compare our targets with other known late T and Y dwarfs in the Solar neighborhood, confirming that there is large intrinsic scatter in the near- and mid-infrared absolute magnitudes and colors of this population, further highlighting the diversity observed spectroscopically by several James Webb Space Telescope (JWST) programs. This scatter makes photometric distance estimates highly unreliable and, therefore, makes astrometric parallax measurements fundamental for a meaningful characterization of even the nearest cold brown dwarfs.

Investigating the apparent anomalies in lithium (Li) surface abundance observed in the Sun and young stellar globular clusters holds significant promise for advancing our understanding of the mechanisms influencing Li depletion. This study delves into the intricate interplay between rotational mixing and rotational hydrostatic effects in pre-main-sequence (PMS) and main-sequence (MS) solar-type stars by employing grids of rotating models. We implement a novel approach in which both the magnetic field strength (B) and the mixing-length parameter (alpha-MLT) vary dynamically with stellar parameters. This avoids fixed values and aims to reduce free parameters while capturing key physical variability. Our models reproduce the observed Li abundance of Sun-like stars (A(Li) = 1.12 dex) consistent with the present-day solar value (1.1 +- 0.1 dex) and yield qualitatively consistent rotational spin-down trends across PMS and MS phases. However, at the solar age (4.57 Gyr), the same models over-predict the equatorial rotation rate (v = 4.72 kms-1 vs. 2.0 kms-1) and the mean surface magnetic field (B = 36.9 G vs. 1 G). These discrepancies reflect the omission of additional angular momentum loss mechanisms and possible oversimplifications in magnetic saturation physics. While the adaptive alpha-MLT converges to the solar-calibrated value ([1.76, 1.78]) at the present age, its variability during earlier phases significantly influences Li depletion. We compare predictions with observational data from 64 open clusters. The results demonstrate that incorporating time-dependent B and alpha-MLT improves Li predictions and captures rotational evolution trends, but cannot yet reproduce the present-day solar rotation and magnetic flux without additional physics. We discuss these limitations and outline future work for a more complete model of solar-type stars.

Measurements of the electron density of populations of extragalactic HII regions in nearby galaxies remain limited, despite the relevance of this quantity for characterizing the porosity of the interstellar medium and the escape of the ionizing radiation. We initiated a project aimed at analyzing the root-mean-square electron density ne_rms, the in-situ density ne and the volume filling factor (phi) of extragalactic HII regions, investigating the dependence of these attributes on nebular and host galaxy properties. We present an image-segmentation methodology for constructing homogeneous HII region catalogues, and apply it to two pilot galaxies: NGC 2403 and NGC 628. We derive ne_rms from their Halpha luminosities and equivalent radii (R_eq), and obtain ne and phi for spectroscopic subsamples. While ne is below 300 cm$^{-3}$, ne_rms is typically one to two orders of magnitude lower, implying that phi is in the range ~$10^{-4}$ to $10^{-1}$. The two galaxies exhibit a similar size-density relation, which breaks for R_eq >~ 50 pc, show at most a weak dependence of ne_rms on galactocentric radius for NGC 2403, and no clear dependence of ne or phi on these parameters. Combining these results with published data, ne_rms presents tentative scaling relations with the median HII region size, the fraction of large regions in the parent galaxy, and the star formation rate surface density. These trends, if confirmed, would provide new constraints for massive cluster formation models and important clues for interpreting dependencies observed at high redshift, underscoring the necessity of consistently extending this analysis to larger samples.

We report here on studies to determine the accuracy of estimated corrections of Ionospheric Faraday Rotation Measure (IFRM) using observations of the Moon with the Very Large Array (VLA) and MeerKAT telescopes. To estimate the IFRM requires an estimate of the total electron content along the line-of-sight to the observed sources (the so-called Slant Total Electron Content, or STEC). Estimating the STEC requires an estimate of the global 2-D map of Vertical Total Electron Content (VTEC) along with the ray path from the telescope to the source. Traditionally, these global VTEC maps have been utilized along with an assumption that the electrons are in a thin shell at a given altitude to provide an estimate of the IFRM as a function of time. We find that this traditional technique significantly overestimates the IFRM - typically by 0.5 to 1.1 rad/m^2 for the VLA, and -0.3 rad/m^2 for MeerKAT. Alternatively, the software package ALBUS utilizes raw data from nearby Global Navigation Satellite System (GNSS) stations, to generate a local estimate of the IFRM as a function of time. ALBUS provides considerably better estimates of the IFRM - accurate to 0.1 rad/m^2 for both the VLA and MeerKAT, provided the stations utilized have known receiver bias values. A byproduct of our study is the establishment of the intrinsic electric vector position angle (EVPA) of the standard polarized calibrators 3C286 and 3C138 from 500 MHz to 50 GHz, using additional VLA observations of the Moon, Venus, and Mars.

The Gaia Space Satellite has transformed the field of Galactic Dynamics by collecting 6D phase space information for hundreds of millions of stars. In 2018, it enabled the discovery of the Gaia Phase Spiral (Antoja et al., 2018), a clear signal in the vertical motion of the stars that reveals how far from equilibrium the Galactic disk is. Seven years after the discovery of this structure, a workshop dedicated to the Phase Spiral took place at the Lorentz Center. Workshop participants summarized the current state of knowledge about the Phase Spiral and identified open questions and key areas to continue progressing in understanding the origin of the Phase Spiral and the physics governing the response of the disk to perturbations. Here, we aim to summarize the content and discussions of this workshop, share the resources that have been produced at this workshop with the broader community, and invite interested individuals to join on the projects that started.

Optimization of the SPHERE-3 detector configuration, designed to study the mass composition of primary cosmic rays in the energy range 1--1000 PeV by registering Cherenkov light reflected from the snow surface, requires simulation of a large number of extensive air shower events. A software suite with a multi-step computational pipeline is presented: shower generation in CORSIKA, decoding and cloning of events (C++/OpenMP), ray-tracing of optical photons through the detector model (Geant4 MT), and approximation of images by a lateral distribution function (Python/multiprocessing, iminuit). The key property of the problem is its natural atomicity: each event is processed independently at all stages, which provides linear scaling under parallel computation. Thread safety is achieved by architectural means -- shared data are read-only, mutable state is isolated per-worker -- without the use of locks on hot paths.

We use Lomonosov-2 supercomputing facility for the generation of extensive air shower events with Cherenkov light which is a rather time consuming procedure. At primary energies slightly below 100 PeV a substantial part of events are killed before reaching their end while exceeding the queue time limit. The fact compelled us to develop a multithread version of the code. We report here the main features of our development as well as some evidence of its efficiency.

We present observations and analysis of two low planet/host mass-ratio ($q$) microlensing planets discovered in high-magnification events. KMT-2025-BLG-0811Lb has $q \sim 4.5 \times 10^{-5}$, and a Bayesian analysis favors a super-Earth/mini-Neptune orbiting an M- or K-dwarf host at a projected separation of $\sim 3$ au. KMT-2025-BLG-0912Lb has $q = 2.6 \times 10^{-4}$ and likely hosts a super-Earth/mini-Neptune around either a low-mass M dwarf or a brown dwarf at $\sim 1$ au. Even with an observing cadence of $\Gamma > 30~{\rm hr}^{-1}$ during the planetary signal, KMT-2025-BLG-0811 still exhibits the "central-resonant" degeneracy. Reviewing nine such events, we find that the "central-resonant" degeneracy can be divided into two distinct types that occupy separate regions in the plane of $q$ and normalized source radius ($\rho$). Type~I events have similar $q$ but substantially different $\rho$ and are more difficult to resolve from the light curves. For Type~II events, the "resonant" solutions have relatively lower $q$ and larger $\rho$. Our review provides guidance for searching for the alternative solution once one solution has been identified.

Photospheric emission from relativistic gamma-ray burst (GRB) jets is a promising mechanism for producing the Band-like spectra observed in the prompt phase, yet the connections between jet structure, dissipation location, and polarization signatures remain unclear. We investigate time-dependent photospheric radiation transfer in structured relativistic jets by coupling two-dimensional axisymmetric special relativistic hydrodynamic (SRHD) simulations with Monte Carlo photon propagation. Photon escape and subphotospheric dissipation are characterized using the residual line-of-sight optical depth tau_out evaluated along each photon trajectory, allowing a direction-dependent treatment of photon decoupling in structured jets. The radiative transfer includes Klein-Nishina Compton scattering and polarization evolution using the Mueller matrix formalism. We perform a systematic parameter study exploring the effects of viewing angle, electron-positron pair loading (Z_pm), and the optical-depth window of subphotospheric dissipation. The model produces time-resolved spectra, peak-energy evolution E_pk(t), Band parameters, polarization degree Pi(E,t), and last-scattering statistics. We find that jet angular structure and the geometry of the line-of-sight optical depth strongly regulate spectral evolution and polarization signatures. The dissipation depth and pair loading jointly control the stability of E_pk, the formation of high-energy spectral tails, and the energy dependence of polarization. These results provide quantitative predictions for GRB prompt-emission spectra and polarization that can be tested with current and upcoming high-energy polarimeters.

To better understand the potential habitability of planets orbiting brown dwarfs, this work presents a new set of equilibrium temperature evolution tracks. Unlike most previous work that relied on analytic scaling relationships for brown dwarf luminosity evolution, we use the outputs of modern brown dwarf evolution models that account for the effects of deuterium burning, cloud formation and dissipation, and the most recent atmospheric opacities. While clouds are present, brown dwarfs cool more slowly than if they did not have clouds, allowing orbiting planets to remain in the habitable zone for millions of years longer than previously estimated. Similarly, we find that during the deuterium-burning phase of brown dwarfs, which also slows the evolution, planets at the same orbital radius but orbiting brown dwarfs of different masses can remain in the habitable zone for the same duration, creating deuterium "sweet spots" for habitability around brown dwarfs near the deuterium-burning limit. For example, at 0.01 AU a planet orbiting both a 0.012 solar mass and a 0.020 solar mass brown dwarf stays in the habitable zone for ~170 - 180 Myr because deuterium burning more strongly affects the cooling of lower-mass brown dwarfs. The size of the effect decreases with decreasing orbital radius, with larger orbital radii having a more pronounced deuterium burning influence. These effects are absent from the analytic cooling approximations used in prior studies of substellar habitable zones and are revealed by our application of modern substellar evolution models.

This paper investigates the dynamical behavior of steady spherical accretion onto a static, magnetically charged black hole embedded in a perfect fluid dark matter (PFDM) background. Using the shadow observations of M87* from the Event Horizon Telescope (EHT), we establish constraints on the parameter space for the magnetic charge and the PFDM parameter. Within this constrained range, we analyze the orbital dynamics of particles in a thin accretion disk surrounding the black hole and find that the black hole parameters significantly influence the effective potential, angular velocity, specific energy, and specific angular momentum of the particles. Subsequently, we calculate the radiative energy flux, temperature profile, and observed spectrum of the disk. Our results show that, while the local radiative flux and temperature at a given radius are lower for the charged-PFDM black hole compared to a Schwarzschild black hole, its overall radiative efficiency and total luminosity are higher. Finally, we explore the spherically symmetric, steady-state accretion process around the black hole, revealing how the parameters govern how the fluid velocity, density profile, and black hole mass accretion rate are influenced.

Radio interferometry enables high-resolution imaging of astronomical radio sources by synthesizing a large effective aperture from an array of antennas and solving a deconvolution problem to reconstruct the image. Deep learning has emerged as a promising solution to the imaging problem, reducing computational costs and enabling super-resolution. However, existing DL-based methods often fall short of the requirements for real-world deployment due to limitations in handling high dynamic range, large field of view, and mismatches between training and test conditions. In this work, we build upon and extend the POLISH framework, a recent DL model for radio interferometric imaging. We introduce key improvements to enable robust reconstruction and super-resolution under real-world conditions: (1) a patch-wise training and stitching strategy for scaling to wide-field imaging and (2) a nonlinear arcsinh-based intensity transformation to manage high dynamic range. We conduct comprehensive evaluations using the T-RECS simulation suite with realistic sky models and point spead functions (PSF), and demonstrate that our approach significantly improves reconstruction quality and robustness. We test the model on realistic simulated strong gravitational lenses and show that lens systems with Einstein radii near the PSF scale can be recovered after deconvolution with our POLISH model, potentially yielding 10$\times$ more galaxy-galaxy lensing systems from the Deep Synoptic Array (DSA) survey than with image-plane CLEAN. Our results highlight the potential of DL models as practical, scalable tools for next-generation radio astronomy.

A large sample of $t_2$ and $t_3$ times from the recent compilation of nova properties given in Schaefer (2025) have been analyzed to determine relationships between these two parameters. Fits were performed in both directions (from $\log t_2$ to $\log t_3$ and vice-versa) to account for the asymmetry inherent in ordinary least-squares regression, which minimizes residuals only in the dependent variable. The following best-fit relations were found: $\log t_3 = (0.877\pm0.019) \log t_2 + (0.444\pm0.027)$, and $\log t_2 = (1.018\pm0.023) \log t_3 - (0.316\pm0.037)$, corresponding to $t_3 = (2.78\pm0.17)~t_2^{(0.877\pm0.019)}$ and $t_2 = (0.483\pm0.041)~t_3^{(1.018\pm0.023)}$, respectively. Within the uncertainties, the latter relation reduces to a simple proportionality: $t_2 \simeq 0.5~t_3$.

The instrumental profile (IP) of a telescope is of great significance for spectroscopic analyses, especially for wavelength calibration and stellar parameter measurements. The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) employs arc lamps for wavelength calibration. These lamps produce sharp emission lines with known wavelengths, and the observed arc lamp spectra can well characterize the IP. However, IPs are influenced by multiple factors, making them difficult to model accurately with traditional methods. Neural networks, which can automatically capture complex patterns and nonlinear features in data, provide a promising approach for high-precision IP measurement. We therefore construct a multi-layer perceptron (MLP) based on The Payne neural network to derive IPs for LAMOST. After training, the model can retrieve the IP for any fiber, at any wavelength, and at any time. We then apply the derived IP to stellar radial velocity (RV) measurements and analyze the impact of different IP center localization methods on the results. Finally, the dispersion of the measured RVs is reduced by approximately 3 km/s. This improvement will facilitate the search for long-period binary stars via RV variations.

High-energy gamma-ray (>GeV) emission of gamma-ray bursts (GRBs) is very important in probing the jet evolution and particle acceleration of GRBs. The observations of high-energy photons are limited except for a few very bright GRBs, hindering precise measurements of the spectral and temporal evolutions of GRBs. Here we report the detection of high-energy gamma-ray emission up to 100 GeV with Fermi-LAT using a stacking analysis of a collection of 330 GRBs. High significance detection of the emission has been found, and the precise light curves and energy spectra can be measured. The light curves and time-resolved spectra of the sub-sample of 220 LAT individually detected GRBs can be well explained by the standard afterglow emission from a population of GRBs with both synchrotron and synchrotron self-Compton mechanisms, assuming a distribution of initial Lorentz factors. However, the emission of the relatively weak sample of the 110 LAT individually undetected GRBs cannot be well reproduced in the same framework, indicating the existence of possible energy injection effect in the GeV band for the first time. The observations hence provide new insights in understanding the high-energy emission of GRBs.

3HWC J0630+186 is one of the very-high-energy gamma-ray sources in the third High-Altitude Water Cherenkov (HAWC) catalog, its origin and source are, however, not clearly identified. The only possible associated source is PSR J0630+19 depart from the center of 3HWC J0630+186. A few TeV halos of pulsars are currently believed the most dominant TeV-PeV gamma-ray sources, and PSR J0630+19 was firstly discovered by Arecibo survey with normal pulsar period, but its age and spin-down luminosity are not available. It is then difficult to determine if 3HWC J0630+186 and PSR J0630+19 are associated or not. With the awarded telescope time in five-hundred-meter aperture spherical radio telescope (FAST) observing cycle, we have obtained the follow-up timing observations of PSR J0630+19 with observed duration more than one year. From our pulsar data analysis, we determined a more precise position and derived parameters via pulsar timing. The parameters indicate that it is an old pulsar with energy loss too low to power the very-high-energy emissions from 3HWC J0630+186.

The advancement in sensitivity and field of view of next-generation wide-field survey telescopes requires astrometric measurements with high precision, even in the presence of significant geometric distortions. To address this challenge, we develop a Weighted Polynomial Distortion Correction in 2-Phase (WPDC-2P) method. This approach enhances stellar cross-matching, incorporates distance-based weighting into the traditional polynomial fitting, and employs a look-up table to absorb the remaining distortion residuals. Validated on simulated data from the Main Survey Camera of the \emph{Chinese Space Station Survey Telescope} (CSST), incorporating geometric distortions up to approximately $200$ pixels, the method achieves astrometric standard deviation ranging from 0.013 to 0.107 pixels (0.03 pixels for the $g$-1 detector) across all 18 detectors. Under extreme crowding conditions (e.g., globular cluster NGC 2298), the astrometric precision for the $g$-1 detector reaches 0.05-pixel level within the central region ($r_d < 4000$), despite a centroiding precision of $\sim$0.04 pixels. When applied to the Beijing-Arizona Sky Survey data, for which the standard pipeline delivers an astrometric uncertainty of $\sim$20 mas, our method reduces the positional scatter to $ \sigma_{\Delta\alpha}=5.494$ mas (0.01 pixels) and $ \sigma_{\Delta\delta}=9.981$ mas (0.02 pixels) using only a weighted 3rd-order polynomial correction. The method has been integrated into the CSST data processing pipeline and is prepared for further refinement using on-orbit calibration data.

Atmospheric aerosols strongly influence daytime sky quality for solar coronal imaging, yet few studies directly link aerosol properties and sky-brightness measurements within ~2° of the Sun. Here we compare externally occulted coronagraphic measurements of near-Sun radiance with aerosol-constrained inferences derived from direct-Sun and sky photometry. Our analysis focuses on Mauna Loa Observatory, a well-characterized high-altitude site for atmospheric and solar observations. We present coronagraphic measurements of near-Sun radiance at 1.54 +/- 0.77° from solar disk center acquired between 2006 and 2007 by an ATST Sky Brightness Monitor (SBM). These data are directly compared with circumsolar radiances inferred at 1.54° using AERONET almucantar measurements and aerosol optical retrievals. We find quantitative agreement between these two approaches, enabling extension to multi-decadal analyses of circumsolar radiance and its relationship to aerosol properties and related proxies (e.g., the Angstrom exponent) using AERONET data from 2000-2025. Near-Sun radiances are expressed relative to the solar disk-center radiance, facilitating direct comparison with related studies. Finally, we synthesize physically based true-color images of the circumsolar sky under representative aerosol conditions as an observational aid, in part to illustrate that visually enhanced solar aureoles do not necessarily imply poor infrared coronal observing conditions. This methodology provides an extended framework for assessing daytime coronal sky quality at existing and future observing sites.

Giant low surface brightness galaxies (gLSBs) are galaxies with extremely extended, faint, optical disks over 50 kpc in radius and have high total masses which can reach 10^12 solar masses. The existence of such galaxies is problematic for current models of galaxy formation, since the major mergers responsible for the large total mass would likely have destroyed the extended optical disk. Examining the gas content of these galaxies is an important step in determining their formation mechanism, whether it be through slow gas accretion or the large disk (re)forming after a major merger. We present neutral atomic hydrogen (HI) observations of 19 gLSBs identified with the Hyper Suprime-Cam Subaru Strategic Program survey. Although most have high HI masses, they are generally lower than expected based on their large optical sizes, and we do identify some gLSBs with unusually low gas content. The HI spectra of these galaxies show evidence for a rotational disk, though these disks are more asymmetric than other galaxies with comparable mass. Four galaxies with similar surface brightness profiles to the gLSBs have also been selected from the Numerical Investigation of a Hundred Astrophysical Objects (NIHAO) simulation for comparison. There is evidence for significant galaxy mergers in the past for three of these NIHAO galaxies and these three galaxies show similar asymmetry in their HI spectra. Together, these results could indicate the large optical disk of gLSBs are the result of a recent merger.

We present a multi-wavelength investigation of radio sources in the globular cluster M22 (NGC6656) using VLA, HST, and Chandra observations. Among the eight identified counterparts, we highlight VLA22 as the most promising stellar-mass black hole (BH) candidate. Its radio and X-ray luminosities follow the established $L_{R}-L_{X}$ correlation for quiescent black hole low-mass X-ray binaries (BH-LMXBs), while its moderately steep radio spectrum and X-ray spectral hardening further support this classification. Analysis of two potential optical counterparts-a bright main-sequence star and a faint subgiant/red giant-suggests a binary system with a relatively long orbital period. The discovery of VLA22 consistent with recent retention models that stellar-mass BH can be retained within globular clusters over Hubble timescales. Additionally, VLA19 exhibits a characteristically inverted radio spectrum ($\alpha = 0.79 \pm 0.39, S_\nu \propto \nu^\alpha$) indicative of a compact jet, while VLA40 also aligns with the BH $L_{R}-L_{X}$ track, though both require further observations to definitively confirm their nature.

We initiate the systematic search for planets in the 2023 data of the Korea Microlensing Telescope Network (KMTNet), focusing on those planets found by the KMTNet AnomalyFinder with low preliminary estimates of the mass-ratio, $q<2\times 10^{-4}$. The 2023 season is the first for which the photometry of all events was re-reduced prior to the AnomalyFinder search, potentially increasing its sensitivity to planets. We find three strong low-$q$ planet candidates, KMT-2023-BLG-0164 ($q\sim 1.3\times 10^{-4}$), KMT-2023-BLG-1286 ($q\sim 1.9\times 10^{-4}$), and KMT-2023-BLG-1746 ($q\sim 8\times 10^{-5}$). KMT-2023-BLG-0164 is notable in that the source is projected on a very bright ($I=16.0$) foreground star, which is either the planet's host or (more likely) a companion to the host. We obtain a spectrum, finding that its mass and distance are $M\sim 1.0\,M_\odot$ and $D\sim 1.5$ kpc, the latter being the distance of the lens ($D_L$) regardless of whether the spectroscopic target is the host or its companion. We also analyze two other candidates, KMT-2023-BLG-0614 and KMT-2023-BLG-1593, which are unlikely to enter the statistical sample due to their ambiguous interpretations as possible non-planetary events.

The habitability of terrestrial exoplanets orbiting M dwarfs is a key topic in the search for extraterrestrial life. The climates of these planets differ significantly from the Earth's due to their likely tidal locking, resulting in a hotter dayside and a colder nightside caused by uneven stellar irradiation. On tidally-locked planets around the outer edge of the habitable zone (HZ), although the definition of the classical HZ requires thick CO2 atmosphere, CO2 can condense onto the surface, leading to the reduction of greenhouse effect. However, the dayside permanent stellar irradiation could maintain a surface liquid water area. The onset of atmospheric collapse and the persistence of surface liquid water are governed by global heat redistribution which is influenced by factors such as atmospheric mass, stellar irradiation, and greenhouse effects. In this study, we used a three-dimensional global climate model to investigate the impact of atmospheric collapse on the presence of dayside surface liquid water. Our results indicate that surface liquid water could counter-intuitively persist despite atmospheric collapse. This is because the loss of atmospheric CO2 weakens not only the greenhouse effect but also daynight heat transport, leading to less redistribution of the energy of dayside insolation to the nightside. While atmospheric collapse is typically seen as an obstacle to maintaining a habitable climate, our findings suggest that it could play a positive role in sustaining surface liquid water on tidally-locked planets. Our work provides new light into the relationship between atmospheric collapse and planetary habitability.

We assess dataset agreement and late-time predictive adequacy in $\Lambda$CDM and its sign-switching extension, $\Lambda_{\rm s}$CDM, using a suite of Gaussian and exact non-Gaussian consistency diagnostics. Both models are constrained with cosmic microwave background measurements from Planck, ACT, and SPT, baryon acoustic oscillation data from DESI DR2, and low-redshift Type Ia supernova data from PantheonPlus+SH0ES. We find that commonly used Gaussian tension metrics can significantly overstate inconsistencies when broad, non-Gaussian posteriors are combined with tightly constrained datasets. In contrast, the exact non-Gaussian parameter shift indicates excellent consistency between CMB and BAO observations in both models. The $\Lambda_{\rm s}$CDM extension modestly improves geometric compatibility at intermediate redshifts, although reductions in parameter-level tension do not necessarily imply improved predictive consistency. These results highlight the importance of exact, non-Gaussian, and predictive diagnostics for robust assessments of cosmological model consistency.

Using multi-wavelength observations from the Solar Dynamics Observatory (SDO), we investigated the six-month decay process of the solar active region NOAA AR 12738 from April to October 2019. We systematically analyzed the region's evolution by examining extreme ultraviolet (EUV) intensity variations, quantifying magnetic flux diffusion, and investigating thermodynamic changes via Differential Emission Measure (DEM) analysis. This study presents the first long-term tracking of a peripheral dimming region (dark moat), revealing its continuous areal decrease over time. DEM results reveal cooling plasma signatures and thermal restructuring, with the dimming region exhibiting a distinct temperature deficit in range 10$^{5.5}$ -- 10$^{5.9}$~K. Potential field extrapolation identifies two dominant magnetic configurations: low-lying loops with cool plasma ($<$10$^{5.5}$ K), and high-arching structures connecting to the AR core, contributing to localized emission reduction. We found that the dimming is dominated by high-lying loops extending from the AR core, which are heated to temperatures above the main response of the 171~Å passband ($>$ 10$^{5.8}$ K), consequently lacking plasma at the typical 10$^{5.8}$~K formation temperature. The thermal deficit, not just the absence of material, is the key driver of the reduced emission. Our results demonstrate that long-duration dimming provides a valuable diagnostic for understanding active region decay, thermal evolution, and coronal magnetic restructuring.

Long-standing optical quasi-periodic oscillations (QPOs) with periodicity of hundreds to thousands of days have been accepted as indicators for central sub-pc binary black hole systems (BBHs) in broad line active galactic nuclei (BLAGN). However, there are so far no direct reports on whether such reported optical QPOs have their periodicities constant in different periods. Here, based on different methods applied to light curves of 4C 50.43 in different periods, optical QPOs with periodicity of 1124days was detected in the CSS V-band light curve, while a shorter periodicity of 513days was detected in the ZTF g/r band light curves. Despite the two periodicities near-harmonic 2:1 ratio, their absence of simultaneous detection in the lomb-scargle periodograms of the ZTF light curves suggests that they are unlikely to be harmonically related. Potential factors were considered to explain these two distinct periodicities, especially different temporal coverage, signal-to-noise ratio and time steps between the CSS and ZTF light curves, as well as the effects of red noises related to intrinsic AGN variability. Our analysis shows that red noises have strong influence on the different periodicities in 4C 50.43 supporting our previous simulations. The results in this manuscript strongly indicate that it should be cautioned for applications of determined optical QPOs in BLAGN having strong intrinsic AGN variability.

Cosmic voids, the underdense regions of the Large Scale Structure (LSS), provide cosmological information highly complementary to that obtained from overdense regions. In this work, we investigate the constraining power of the void-shear cross-correlation (void lensing effect) on the total neutrino mass. Based on cosmological simulations with varying neutrino masses, we identify voids with the DIVE void finder and obtain their density profiles from the underlying dark matter and neutrino distributions. We then generate mock shear catalogues through ray-tracing and measure the corresponding void lensing signals. Our results show that void lensing yields an independent constraint on total neutrino mass as $\sigma(M_{\nu})=0.096\,{\rm eV}$ in the absence of shape noise, and $\sigma(M_{\nu})=0.340\,{\rm eV}$ when adopting a Stage-III-like shape noise ($\sigma_e \simeq 0.3$). Moreover, we find a clear linear relationship between the void lensing signal and neutrino mass. We further validate the forward modelling of the void lensing signal from the void density profiles across different cosmologies, demonstrating its accuracy and potential for future applications. These findings highlight void lensing as a promising probe of massive neutrinos and motivate its applications to galaxy survey data as well as the combination with other cosmological observables.

As plans for the construction of third-generation gravitational wave (GW) detectors advance, research into strongly lensed GWs has become increasingly critical. It is anticipated that hundreds of multi-image lensed GWs will be detected annually. We present a comprehensive suite of lensed GW mock catalog derived from a composite lens mass model incorporating dark matter halos, galaxies, and subhalos. We analyze three source populations with four detector network configurations considering the earth rotation. Our simulations encompass not only conventional doublets and quadruplets but also subhalo-lensed events, highly magnified systems, and complete three or five image systems with a detectable central image, a feature distinct from optical lensing. For the joint ET+CE network, we forecast an annual detection rate of approximately 400 doublets and 36 quadruplets. Notably, this population includes roughly 107 events lensed by subhalos and 20 complete systems with detectable central images. Furthermore, we analyze high-magnification events ($\mu > 3$), predicting approximately 360 such cases. Under a more relaxed selection criterion that requires only at least one lensed signal to exceed the detection threshold, we estimate a total of approximately 617 lensed events. We also investigate the impact of variations in lens mass models and stellar evolution models on event rates, as well as the distributions of SNR pairs and time delays. These results establish a more physically grounded statistical prior for the future identification and authentication of lensed GW signals. The Gravitational Waves-Lensing Mock Catalog (GW-LMC) have been made publicly available.

Longitudinal density fluctuations observed in stellar streams can result from gravitational interactions with massive perturbers in the Milky Way, such as dark matter subhalos. Analysing these density variations provides a powerful probe of properties (motion, mass, size, etc.) of the perturbing objects. However, caution is needed because density variations may arise naturally from internal dynamics of streams, namely epicycles. In this work, we focus on the Indus stellar stream, a remnant of an ancient dwarf satellite of the Galaxy. An Indus stream spanning $\sim 90^\circ$ is revealed in the southern Galactic sky using a comprehensive matched-filter analysis utilizing data from the Gaia mission. A spatial density model is fitted to the filtered map to quantitatively characterize the morphology, which demonstrates episodic density peaks and gaps in the stream. Through N-body simulations, we show that there are strong epicyclic motions of stars happening during tidal disruptions. The present-day longitudinal densities from simulations are comparable to the measurement from data, with similar numbers and locations of peaks and gaps, suggesting that the observed density should mainly be caused by epicycles. We also find that a cuspy dark matter halo for the Indus dwarf is likely to produce milder stellar epicyclic peaks compared to a cored halo which results in steeper peaks. This arises from different instantaneous mass loss due to distinct central mass distributions of halos, where a cored halo usually leads to severer tidal stripping. The observed density exhibits moderate peak sharpness, implying that Indus may have originally possessed a cuspy halo.

Dark matter comprises ~85% of the entire mass of the Universe, but the fundamental nature of its constituent particles remains elusive. In this thesis, I test for two competitive dark matter models: the conventional heavy particle paradigm, and dark matter being ultralight bosons of mass $\sim 10^{-22}$eV ($\psi$DM). More specifically, I test for the faint-end turnover induced by $\psi$DM models, exploiting the strong lensing power by massive galaxy clusters to probe intrinsically fainter magnitudes. A key challenge for such an analysis would be contamination by low-z galaxies sharing similar observed SEDs as high-z galaxies. As I will demonstrate, such a contamination issue is generally severe and may wash out the faint-end turnover signatures. I also show that $\sim 50\%$ of the purported $3.5\leq z\leq 5.5$ galaxies within existing photometric redshift catalogs constructed for Hubble Frontier Fields (HFF) are in fact low-z interlopers. Luckily, individual mitigation of interlopers can be achieved with the combination of deep HST and JWST observations. For fields without supplementary data, machine learning methods will be shown useful in preserving the mitigating power. Cleaner $3.5\leq z\leq 5.5$ and $6\leq z\leq 10$ samples are derived for a more reliable test in strong lensing field of MACS J0416, with which I found no evidence for faint-end turnovers, leading to a constraint on the $\psi$DM mass of $>2.97\times10^{-22}$eV at 95\% confidence. This constraint will also be interpreted in an scheme where dark matter is composed of multiple particle copies, where I argue the derived mass bound is likely on an effective de Broglie scale governing the collective behavior of the entire $\psi$DM budget under gravitational equilibrium established.

The detection of life on rocky exoplanets in the habitable zones of nearby stars would be a paradigm-shifting advance, and it is one of the greatest scientific challenges of our time. There is no single spectral feature that is an unambiguous sign of life on a given exoplanet. Instead, the current state-of-the-art approach involves detecting multiple molecular atmospheric features that should not exist together in equilibrium, e.g. simultaneous detection of O$_2$ and CH$_4$. Spectra across a wide wavelength (0.3-1.7 $\mu$m) range are necessary to cover multiple spectral features per molecule of interest and to contextualise the suite of molecular features detected. While the US will lead the optical arm of the Habitable Worlds Observatory (HWO) coronagraph, a UK-led contribution of a near-infrared Integral Field Spectrograph (IFS) for the infrared arm will ensure UK leadership in the flagship scientific goal of HWO - to search for signatures of life on potentially habitable exoplanets.

Context: Rotating anisotropic convection generates differential rotation in stellar convection zones. Aims: The main aim is to compute the non-diffusive contribution ($\Lambda$ effect) to angular momentum transport, described by Reynolds stress, from rotating turbulent convection. Methods: Rotating hydrodynamic convection is simulated in Cartesian geometry at different latitudes and rotation rates. Large-scale flows are suppressed such that the Reynolds stress is due to non-diffusive effects. Results: The radial angular momentum flux is downward (outward) for slow (fast) rotation. This is in contrast in prevailing theories in mean-field hydrodynamics where the radial transport is always downward. The outward transport at rapid rotation is due to thermal Rossby waves that manifest as elongated large-scale convection cells near the equator. The horizontal angular momentum flux is always equatorward, with increasing concentration toward the equator as in earlier Cartesian studies. The magnitudes of the $\Lambda$ effect coefficients are roughly an order of magnitude lower than in the case of anisotropically forced turbulence or in analytic theories. Conclusions: The current results highlight the tension between numerical simulations, widely used mean-field models, and solar observations. The mean-fields models have been remarkably successful in reproducing solar differential rotation but underlying assumptions regarding turbulence in these models seem to be at odds with 3D simulations. The current simulation results for the vertical (radial) angular momentum transport are in accordance with spherical shell simulations, where thermal Rossby waves are responsible for the generation of equatorial acceleration or solar-like differential rotation. Thermal Rossby waves are absent in the turbulence models of current mean-field theories and they have not been unambiguously detected in the Sun.

We have incorporated a hadron interaction tuning based on accelerator data into our atmospheric neutrino flux calculation, which has been used to analyze atmospheric neutrino oscillations at Super-Kamiokande. This new approach enables a more direct evaluation of the flux uncertainty than a conventional tuning using atmospheric muons. The neutrino flux calculated with this new tuning is 5\%--10\% smaller but still consistent with our previously published prediction within its uncertainty. The flavor ratio $(\nu_{\mu}+\bar{\nu}_{\mu})/(\nu_e+\bar{\nu}_e)$ and $\bar{\nu}/\nu$ ratios were consistent with the previous prediction. Based on the measurement errors of the accelerator data, we evaluated the flux uncertainty associated with the new tuning to be 7\%--9\% in the $E_{\nu} <$ 1 GeV region, which was difficult to assess with the conventional tuning. The flux uncertainty in the $1<E_{\nu}<10$ GeV region was evaluated to be 5\%--7\%, which is an improvement over the conventional tuning.

A large fraction of the extragalactic sky is obscured by foreground dust and stars along the plane of the Milky Way, leaving a major gap (~ 20%) in whole-sky maps of large-scale structures -- an incompleteness that is even more severe for peculiar velocity samples. This has long limited an unambiguous interpretation of observed cosmic flows and their connection to the underlying mass-density field. We present a new hybrid reconstruction methodology which combines 65,518 galaxy peculiar velocity distances from the CF4++ catalogue (Courtois2025) with 8283 new galaxy redshifts observed near the southern Galactic plane (|b| <= 10 degrees) Zone of Avoidance. A major advance is the inclusion of 2176 high-sensitivity, interferometric HI redshifts obtained with the SARAO MeerKAT telescope which for the first time provide coverage of the innermost 3degrees-wide strip of the southern ZOA and to unprecedented depth. This hybrid redshifts & peculiar velocities approach yields a substantially revised view of the inferred overdensities in and around the ZOA. In particular, the Vela supercluster emerges as a dominant mass concentration, rivaling the Shapley concentration and exceeding the mass associated with Laniakea and the Great Attractor region. With a total mass of 33.8 10^16 Msol, a characteristic radius of 70 hmpc, and a double core morphology at a distance of 189 hmpc, Vela dominates the mass budget and gravitational influence of the southern Zone of Avoidance. These results provide the most complete and dynamically consistent picture to date of the southern Zone of Avoidance and demonstrate the transformative potential of hybrid reconstruction techniques tailored for the next generation of large-scale surveys.

Screening mechanisms are essential components in many modified gravity theories, which satisfy local tests of General Relativity (GR) and address cosmic acceleration on cosmological scales. The strong gravitational lensing of gravitational waves (GWs) offers a unique observational probe into cosmology and fundamental physics. In this paper, we investigate the possibility of testing screened modified gravity theories with strongly lensed gravitational waves. Specially, we develop the refined theoretical and statistical framework, in order to measure the post-Newtonian parameter $\gamma_{\text{PN}}$ in the presence of screening effects. Specially, the mass-truncated power-law and Navarro-Frenk-White (NFW) models are introduced to quantify the modified lensing potential. Our analysis also addresses the mass-sheet degeneracy (MSD) problem, by incorporating the absolute magnification and time delay measurements accessible through strongly lensed GW systems. We find that individual lensed GW system detected by next-generation GW detectors can provide stringent constraints on the PPN parameter ($\gamma_{\text{PN}}$) across different screening scales ($\Lambda$). Therefore, future measurements of strongly lensed GWs have great promise to seek departures from GR on kpc-Mpc scales, due to more precise time delay from lensed GW signals.

The cores of wide-orbit giant planets can form via pebble accretion if large planetesimals form in the outer regions of protoplanetary discs at sufficiently early times. Streaming instability simulations support mass distributions consistent with Solar System minor body constraints, but when and where planetesimal formation took place remains uncertain. Here, we report on our N-body simulations of core formation through pebble and planetesimal accretion starting from streaming-instability inspired planetesimal mass distributions. We explore two initial radial planetesimal distributions, a ring-like and a spatially more uniform distribution, between 10 and 50 AU. To address the numerical challenge of simulating realistic planetesimal numbers, corresponding to one to ten Earth masses of planetesimals, we made use of GPU acceleration for the N-body interactions (with GENGA) and a newly developed pebble accretion module. We find that the top of the planetesimal mass distribution provides the seeds for core formation through pebble accretion, leading to the formation of multiple giant planets. This is consistent with previous studies not including N-body interactions. Planetesimal surface densities, crudely corresponding to an initial 10% formation efficiency, imply low mean collision rates (around unity) in the gas disc phase. Our simulations show that giant planet formation depends only weakly on the initial locations where planetesimals form, because of rapid dynamical scattering, and on their total mass budget, due to filtering of the pebble flux between embryos. After disc dissipation, giant planet systems stir the remnant primordial planetesimals, making a scattered disc an inherent outcome of giant planet formation. Giant impacts between planetary cores generally appear to be rare in the first 100 Myr.

Accurate and automated galaxy redshift determination is essential for maximizing the scientific return of spectroscopic surveys. In this paper, we propose a data-driven method to address this challenge. The method first learns a rest-frame representation of galaxy spectra using Non-negative Matrix Factorization (NMF). The method then reconstructs new spectra using this representation at different trial redshifts, and identifies the correct redshift by selecting the one that minimizes the reconstruction error. We apply our method to galaxy spectra from the Multi Unit Spectroscopic Explorer (MUSE), covering redshifts from 0 to 6.7. Our method achieves an overall success rate of 93.7%. We further demonstrate two applications: (i) the separation between true and false sources, and (ii) the detection of blended sources from one-dimensional spectra. Our results demonstrate that NMF-based representations provide a powerful and physically motivated framework for redshift estimation in current and future large spectroscopic surveys.

Stochastic particle acceleration in turbulent plasmas plays a key role in shaping high-energy emission from relativistic outflows, such as those in Active Galactic Nuclei (AGN) and microquasars. While traditional Fermi-II models provide a foundational framework, they often oversimplify the complex nature of realistic magnetohydrodynamic (MHD) turbulence, especially in high-amplitude ($\delta B/B_0 \sim 1$) and relativistic regimes. Recent plasma simulations for these conditions have revealed highly non-linear energization effects, such as sudden, large momentum jumps, that remain largely unexplored in astrophysical applications. We present a novel Monte Carlo framework STRIPE that models particle acceleration as a continuous-time random walk (CTRW), capturing both intermittent energy gains and radiative losses. The stochastic evolution of particle momenta is driven by jumps with random magnitudes determined by a distribution of magnetic-field-line velocity gradients, with synchrotron and inverse Compton cooling incorporated self-consistently. Using STRIPE, we explore particle acceleration under physical conditions characteristic of TeV-PeV $\gamma$-ray emitting microquasars recently identified by Large High Altitude Air Shower Observatory (LHAASO). We find that relativistic, high-amplitude turbulence naturally produces particle spectra with steep low-energy cutoffs, and hard extended power-law high-energy tails reaching tens of PeV. These features differ markedly from standard quasi-linear theory and are well suited to explaining the unexpectedly hard TeV-PeV spectra of LHAASO-detected microquasars. These results highlight turbulent acceleration in the relativistic regime as a promising mechanism for particle energization in microquasar systems, as well as potentially other extreme astrophysical environments.

Pure natural inflation is a compelling effectively single-field model of inflation stemming from a top-down approach to the acceleration mechanism. In this short letter we show that such model is compatible with the latest CMB constraints from the Atacama Cosmology Telescope. Under both the instantaneous reheating hypothesis and standard assumptions for reheating, we rule in a non-trivial fraction of the parameter space. We apply our analysis also to a phenomenological extension of the model and chart its viable parameter space.

The parameter $S_8$, a key probe of cosmic structure growth, exhibits a persistent $\sim3\sigma$ tension between high-redshift measurements from cosmic microwave background (CMB) anisotropies and low-redshift weak gravitational lensing observations. This discrepancy may indicate either unaccounted systematic effects or new physics beyond the standard $\Lambda$CDM cosmology. In this work, we constrain $S_8$ using the high purity CatNorth 1.5 million quasar candidate catalog and the {\it Planck} DR4 CMB lensing data across the broad redshift ranges through auto-correlation and cross-correlation analyses. To address the spatial incompleteness, we develop a machine-learning-based selection function that effectively suppresses the systematics-induced power spectrum excess on large scales. Our robust low-redshift measurements at $z<1.5$ yield $S_8 = 0.844^{+0.058}_{-0.056}$, consistent with the {\it Planck} 2018 CMB anisotropies constraints of $S_8=0.834\pm0.016$ but lower than the $0.879^{+0.055}_{-0.055}$ reported by a previous work using the Quaia quasar candidate catalog. However, for high-redshift faint quasars at $z>1.5$, we find a lower value of $S_8=0.724^{+0.058}_{-0.054}$, likely due to the sample incompleteness and/or the foreground contamination. Further tests on the volume-limited samples exhibit a consistent trend: $S_8 = 0.835^{+0.053}_{-0.049}$ for $z < 2$, $0.824^{+0.061}_{-0.062}$ for $0.4 < z < 1.5$, and a lower value of $0.789^{+0.062}_{-0.062}$ for the higher redshift range of $1.5 < z < 2.5$. While future data may refine these results, our current measurements based on a large sample of quasar candidates show less evidence of the $S_8$ tension.

Extreme solar particle events reveal that the Sun can occasionally produce eruptions significantly more energetic than those observed in the modern era. These events are thought to originate from powerful coronal mass ejections, typically associated with large solar flares triggered by magnetic field reconnection in complex active regions. Stellar observations indicate that Sun-like stars can host superflares exceeding 10^34 erg roughly once per century, yet it remains uncertain whether the Sun can reach such flare energies. We empirically estimate the upper limit of solar flare energies using statistical relations between flare - ribbon areas and released energy derived from modern observations. By extrapolating these upper-envelope relations to the largest sunspot group recorded since 1859 - the Great Sunspot of 8 April 1947 - we find that exceptionally large and complex solar active regions could, in principle, produce flares with bolometric energies of a few 10^34 erg.

We present the first on-sky demonstration of dual-field interferometry at the CHARA Array and the first direct resolution of the inner Ba--Bb subsystem in the bright hierarchical triple $\alpha$ Piscium. Using $H$-band fringe tracking on component A with MIRC-X to stabilize $K$-band science fringes on component B with MYSTIC, we detected a companion at a projected separation of 7 mas, confirming a long-suspected but previously unresolved short-period subsystem within the B component. The nearly equal $H/K$-band flux ratio indicates that Ba and Bb are near-twin F-type stars, consistent with the two narrow-lined components seen in optical spectra of B. By combining CHARA interferometry with archival VLTI/GRAVITY astrometry and radial velocities from archival and new spectroscopy (NARVAL and ARCES), we derive a well-constrained orbit with a period of $P = 25$ d, eccentricity $e \simeq 0.6$, and inclination $i \simeq 65^\circ$, yielding precise dynamical masses of $1.668\pm0.033\,M_\odot$ and $1.646\pm0.029\,M_\odot$. No additional companion is detected down to $\Delta H \approx 5$ at separations of 0.2--2 AU. We also obtained dual-field differential astrometry of the wide A--B pair with a precision of ~0.234 mas at a separation of $1.85''$, with an error budget dominated by internal delay-line actuators, fringe-tracking performance and chromatic dispersion. While the long-period outer orbit is not refined by these measurements, their agreement with the published astrometric orbit provides an on-sky validation of the CHARA dual-field mode. These results establish $\alpha$ Psc as a well-characterized hierarchical system suitable for future benchmark studies and demonstrate CHARA's new capability for off-axis interferometry and sub-mas astrometry on arcsecond-scale binaries.

Studying the interaction between core-collapse supernova remnants (SNRs) and their surrounding environments is essential to understanding the mechanism for energy transfer to the interstellar medium (ISM) and the intrinsic physical properties of these remnants. In this paper, we focus on G309.8-2.6. Our new observations reveal that this object includes an SNR shell with a relic pulsar wind nebula (PWN) that extends well beyond the emission that has been previously observed in X-rays. We present new radio continuum and polarization images of G309.8-2.6 from the Evolutionary Map of the Universe (EMU) and Polarization Sky Survey of the Universe's Magnetism (POSSUM) surveys with the Australian Square Kilometre Array Pathfinder (ASKAP). The images reveal the complex and peculiar morphology of G309.8-2.6. The linear polarization displays an atypical S-shaped morphology and a highly ordered magnetic field. The rotation measure (RM) map shows a large-scale gradient or possible sign reversal, depending on the foreground RM. We reprocessed archival X-ray observations from Chandra and eROSITA, and retrieved archival H$\alpha$ and infrared observations. We performed a joint analysis of the multiwavelength data and proposed scenarios to explain the unusual shape. Our results place new constraints on the magnetic field of G309.8-2.6, including its environment, and demonstrate the power of polarization observations in probing the properties of SNRs.

We aim to develop a model-driven deep learning approach to age determination, by training neural networks on stellar evolutionary grids. Contrary to the usual data-driven deep learning approach of using prior age estimates as training data, our method has the potential for a wider and less biased range of application. The low computational cost of deep learning methods compared to bayesian isochrone-fitting allows for a broad analysis of large spectroscopic catalogues. We train multilayer perceptrons on different stellar evolutionary grids to map [M/H], MG, (GBP - GRP) to stellar age ${\tau}$. We combine Gaia photometry and parallaxes, metallicities and ${\alpha}$ elements from spectroscopic surveys and extinction maps, which are passed through the neural networks to estimate stellar ages. We apply our method to the LAMOST DR10, GALAH DR3 & DR4 and APOGEE DR17 spectroscopic surveys, for which we estimate the ages using the BaSTI tracks, along with other stellar evolutionary models. We leverage this novel technique to study, for the first time, differences in age estimates from several evolutionary grids applied on very large datasets. In addition, we date 13 open clusters and one globular cluster and find a median absolute deviation with literature ages of 0.20 Gyr. Along with the stellar ages catalogues from our estimates, we release NEST (Neural Estimator of Stellar Times), a python package to estimate stellar age based on this work, as well as a web interface. We show that, when using the same evolutionary grid, our method retrieves the same ages as a bayesian approach like SPInS, for only a fraction of the computational cost, with a 60,000 speedup factor for a typical star. This model-driven deep learning technique thus opens up the way for broad galactic archeology studies on the largest datasets available today and in the near future with upcoming surveys such as 4MOST.

Turbulence plays a critical role in the atmosphere, oceans, engineering, and astrophysics. The dissipation (heating) induced by turbulent flows is particularly important for the thermodynamics and chemistry of interstellar clouds, yet its structure and statistics remain poorly understood. Using high-resolution turbulence simulations with controlled explicit viscosity, we study the kinetic energy dissipation rate, $\varepsilon_{\mathrm{kin}}$, across subsonic and supersonic regimes. We find that dissipation lags large-scale kinetic energy injection events by $1.64\pm0.21$ and $0.48\pm0.07$ turbulent turnover times in subsonic and supersonic turbulence, respectively. Correlations show $\varepsilon_{\mathrm{kin}}\propto\vert\nabla\times\mathbf{v}\vert^2$ (vorticity squared) in the subsonic regime, where density fluctuations are negligible, while in the supersonic regime dissipation is primarily correlated with density, $\varepsilon_{\mathrm{kin}}\propto\rho^{3/2}$. A spectral analysis demonstrates that achieving numerical convergence of $\varepsilon_{\mathrm{kin}}$ across all scales is challenging, especially in the subsonic case, even at $2048^3$ resolution. Nonetheless, subsonic dissipation is clearly localised on small vorticity-dominated scales, while supersonic dissipation spans many scales, combining elongated, thin shocks with small-scale vorticity. Finally, we determine the fractal dimension of $\varepsilon_{\mathrm{kin}}$. In the subsonic regime, intense dissipation is predominantly organised in flattened vortex filaments embedded in thin shearing layers on small scales, becoming more volume-filling at larger scales. In the supersonic regime, $\varepsilon_{\mathrm{kin}}$ exhibits a fractal dimension between 1 and 2 across nearly all scales, likely reflecting shock surfaces and their intersections forming filaments.

Tidal Disruption Events are exotic astrophysical phenomena where matter from a star or the interstellar medium is captured by a supermassive black hole. The process liberates enormous energy, within a few months to a year timescale, enough to detect dormant black holes in near as well as the farthest galaxies. We revisit the long-term spectral variabilities associated with the jetted Tidal Disruption Event \source~by exploring the archival X-ray data obtained with MAXI/GSC, Swift/XRT, and XMM-Newton observatories. Our analysis reveals that the spectral indices decrease non-monotonically as \source~evolves with time. We also find that the soft (0.3-1.5 keV) and hard (1.5-10 keV) X-ray photon counts are highly correlated with a maximum correlation coefficient of 0.95 and peak at {\it zero} lag. Moreover, the soft and hard band variabilities obtained from XMM-Newton observations are highly correlated with a Pearson cross-correlation coefficient of 0.96. This indicates that the soft and hard X-ray photons are emitted from the same site, which is most likely a Compton cloud, i.e., the corona. Assuming the hard X-ray photons originate from the corona, we find that the coronal parameter undergoes rapid expansion during the early phases when accompanied by a relativistic jet launching and subsequently evolves toward a state of saturation with minor fluctuations in the latter stages. The temporal variation of the coronal size is consistent with a simple theoretical conjecture. We also discuss the application of our analytical outcomes to other jetted and non-jetted tidal disruption events.

The High Energy Rapid Modular Ensemble of Satellites (HERMES) instrument is a compact X/$\gamma$-ray spectrometer operating on board the 6U (11 kg) SpIRIT CubeSat. The payload is particularly well suited for the observation of cosmic transients such as Gamma-Ray Bursts and bright pulsars thanks to its unique broadband sensitivity from a few keV to a few MeV and the temporal resolution down to half a microsecond. We report here the detection of the $\sim$33~ms Crab pulsar double-peaked pulse profile obtained by considering the canonical Crab ephemerides as provided by the Jodrell Bank catalog. We collected approximately 5.7$\cdot$10$^4$ photons from 730~s of observations, in the 3 keV -- 2 MeV energy band, during a single operation, and achieved a 5$\sigma$ pulse profile significance in the 3--11.5 keV energy band with binning at the ms scale. The results demonstrate that SpIRIT/HERMES can achieve millisecond timing accuracy at high energies and, thanks to its wide field of view and broad energy band, has the potential to contribute to GRB monitoring in the near future. Such capabilities were previously the domain of flagship observatories, underscoring the performance of the HERMES instrument with its compact form factor.

The spin periods of magnetars and X-ray dim isolated neutron stars (XDINS) cluster within a remarkably narrow range. Using the current sample of 30 magnetars with measured periods (ranging from 0.33 to 11.78 s) and 8 XDINS (ranging from 3.45 to 12.76 s), we utilize the point-likelihood technique to constrain the birth and final periods of these sources, assuming a steady-state population. Employing a general braking law characterized by a constant braking index $n$, we find that for $n > 2$ the final (cut-off) period of magnetars is constrained to $P_f \simeq 11.8 - 12.0$ s and XDINS to $P_f \simeq 12.8 - 14.9$ s, at the 95 per cent confidence level, while the birth periods remains largely unconstrained for dipole spin-down ($n=3$) as in earlier work. The slight increase in the upper cutoff from $\sim$12 to $\sim$15 s over two decades of discoveries of new sources, yielding a threefold increase in the known magnetar population, and the extension of the minimum period to $\sim 0.33$ s strongly support a physical origin for this clustering. We discuss this result in the context of magnetic-field-decay models and fallback-disc torque-equilibrium scenarios. The combined magnetar and XDINS sample (38 sources) yields the tightest constraints on $P_f\simeq 12.8-12.9$ s, for $n=3$, suggesting possible evolutionary connections between these populations and pointing toward a common physical mechanism that terminates the observable phase of these neutron stars at periods near 14 s.

We present a study of recent star formation in the dwarf irregular galaxy DDO 43 using GALEX FUV and WISE NIR imaging. We identify regions of elevated FUV flux, indicating unobscured star-forming activity across much of the galaxy. To further characterize the stellar content, we compare the FUV fluxes to archival WISE W1 and W2 infrared data across 56 regions of interest. A general correlation is found between the FUV and infrared fluxes, suggesting spatially coherent star formation throughout the galaxy. A few regions, however, show elevated infrared fluxes but little or no UV emission, potentially indicating localized, dust-obscured star formation.

Fast X-ray transients (FXTs) have been detected for over a decade, yet their origins are still enigmatic. The observed association between FXTs and broad-lined Type Ic supernovae (SNe Ic-BL) suggests that some may share the same progenitor with Long Gamma-Ray Bursts. In this work, we numerically simulate the long-term evolution of a relativistic jet propagating from inside the progenitor star up to the photon diffusion radius of the cocoon. Then we post-process the hydrodynamic results and calculate the cocoon cooling emission for various viewing angles from the jet axis. We find that, for viewing angles $\theta_{\rm v}=10^{\circ}$--$20^{\circ}$, the off-axis cocoon emission can produce FXTs with luminosity $L_{\rm X}\simeq 10^{47-48} {\rm\, erg\,s^{-1}}$ and duration $t_{\rm X}\simeq 10$-$100\,$s. The observed spectra are quasi-thermal with the peak energy $E_{\rm peak}\simeq0.8$ keV. These properties naturally explain FXTs' observational features, including their high luminosity, soft spectra, and lack of gamma-ray counterparts. The Rayleigh-Jeans tail of the FXT spectra extends to the UV, producing an early UV flash simultaneously. As the cocoon expands and cools, the emission peak shifts to UV and optical bands, resulting in a bright optical plateau lasting for $\sim1$ day with color temperature $T_{\rm UV/opt} \simeq (1{-}3)\times10^{4}\,$K, before the emergence of supernova emission. Although our model underpredicts the UV/optical luminosity at $\sim1$ day, it still provides useful diagnostics for identifying the origins of FXTs.

Protoclusters represent sites of accelerated galaxy formation and extreme astrophysical activity characteristic of dense environments. Identifying massive protoclusters and mapping their spatial structures are therefore crucial first steps in understanding how the large-scale environment influences galaxy evolution. We combine wide-field Ly$\alpha$ imaging from the ODIN survey with extensive DESI and ancillary spectroscopy across the extended COSMOS and XMM-LSS fields ($\approx$14 deg$^2$) to search for massive protoclusters. We confirm six systems at $z\approx 2.4$ and $z\approx 3.1$, reconstruct their three-dimensional structures, estimate descendant halo masses, and, for one structure at $z\approx 3.12$, demonstrate that overlapping narrowband filters ($NB497$ and $N501$) provide accurate redshift tomography for emission-line galaxies. One protocluster at $z\approx 2.45$ overlaps with one of the LATIS tomographic fields, enabling direct comparison between galaxy and H {\sc i} overdensities traced by Ly$\alpha$ forest absorption. Another at $z\approx 3.12$ hosts a massive quiescent galaxy ($M_{\ast} \approx 1.2 \times 10^{11}M_\odot$), indicating early quenching in a dense environment. By comparing Ly$\alpha$ emission properties across environments, we find that protocluster galaxies exhibit higher median line fluxes and a deficit of faint emitters relative to the field. The effect is strongest when both 2D and 3D density information are combined, indicating that galaxies in the densest protocluster cores are most affected by environmental processes. This effect is stronger at $z\approx3.1$ than at $z\approx2.4$, suggesting possible redshift evolution.

A recent study suggests that CM chondrite-like planetesimals formed in the vicinity of Saturn, in a pressure bump outside the gap carved by proto-Jupiter. While a fraction of these objects was implanted into the asteroid belt as a consequence of Saturn's growth, it remains unclear whether the scattered remainder could reach the ice-giant region and mix with more distant carbonaceous reservoirs. We test whether outward scattering during Saturn's growth and migration can implant CM-like bodies onto long-lived orbits in the Uranus-Neptune region, where they could contaminate the CI reservoir. We performed N-body integrations of 100 km planetesimals launched from the outer edge of Jupiter's gap, including gas drag and the gravitational perturbations of growing Jupiter and Saturn, with optional inclusion of a nearby ice-giant embryo. We explored a range of gas surface-density profiles and growth timescales. While Saturn's growth efficiently scatters CM-like planetesimals, fewer than about 2 percent are implanted beyond 15 au, even under gas-rich conditions, because gas drag damps their eccentricities and drives them back toward their perihelia rather than allowing them to circularize at larger distances. Adding an ice-giant core modestly increases the outward reach (up to about 4 percent in the most gas-rich case), but Type-I migration further lowers perihelia, making long-term retention at large distances difficult. For a CM mass budget M_CM,tot about 1 M_Earth, this implies at most M_CM < 0.02-0.04 M_Earth reaches 15-25 au, corresponding to a diluted mass fraction < (1-2) x 10^-3 in the outer ring, hence negligible contamination of the CI reservoir. Combined with the distinct radial distributions of CM- and CI-like asteroids in the belt, these results imply limited mixing of carbonaceous reservoirs and isolation of the CI reservoir.

Large time-domain sky surveys generate extensive multi-year catalogs of light curves in which scientifically valuable transients, such as supernovae (SNe), are vastly outnumbered by artifacts and routine star variability. While supervised machine learning models can efficiently filter known classes, they struggle with extreme class imbalance and may overlook rare or novel events. Conversely, unsupervised anomaly detection provides broad discovery potential but lacks targeted sensitivity. We present a hybrid strategy that integrates a supervised SN probability score (SN-score) into the PineForest active anomaly detection framework to enhance SN discovery rate in the 23rd data release of the Zwicky Transient Facility. We train a binary classifier using light-curve features of spectroscopically confirmed SNe from the ZTF Bright Transient Survey, achieving a ROC-AUC approximately 0.98. Incorporating the SN-score as an additional feature, together with a small set of labeled priors, significantly accelerates the discovery of SN-like transients across ten extragalactic ZTF fields. This method increases discovery efficiency without compromising the ability to identify diverse astrophysical anomalies. Application of the combined methodology resulted in the discovery of seven previously unreported SN candidates, one AGN candidate, one unusual Galactic variable star SNAD283, as well as two host galaxies exhibiting multiple supernova events. These results demonstrate its value for scalable and expert-guided transient search in current and future surveys, including the Vera C. Rubin Observatory Legacy Survey of Space and Time.

Binaries and higher order systems can experience mass transfer events between their components. The angular momentum carried by the gained mass can change the observable parameters of the accretor and spin it up to critical rotation. In this work, we aim to explore the spin-up effect of direct accretion through a stream as a possible mechanism for an accretor to gain more than a tenth of its initial mass without acquiring enough momentum to reach critical rotation. We present a novel analytical model to characterize the effects of direct mass transfer on the accretor's measurable parameters as a function of the binary's semi-major axis and eccentricity and the donor's rotation velocity. This model takes a two-body approach to the problem, where a stream is decomposed as many discrete particles that do not interact with each other and are influenced by the accretor's gravitational potential only. Each parcel has an instant orbital solution derived from its initial conditions. The contribution each accreted parcel has to the total spin-up of the accretor is given by its tangential velocity at impact, through conservation of angular momentum. Direct mass transfer proves to be inefficient at spinning up the accretor and thus enables the star to gain a great fraction of its initial mass without reaching critical rotation. We also quantify the fraction of mass that directly impacts the accretor in contrast to the mass that is either lost from the system or creates a disk around a star. Our results show that systems are the most mass-conservative when the orbit is tighter or when the donor's spin is greater. In terms of eccentricity, the conservation of mass shows mixed results depending on the system's other initial properties. However, systems with higher eccentricity are consistently a hundred percent conservative within our parameter space.

If a gravitational wave event is lensed by a cluster or galaxy in our line-of-sight, it is expected that its host galaxy would also be lensed. Therefore, connecting lensed gravitational wave events even without direct optical counterpart could be feasible by identifying matching lenses in electromagnetic data and surveys. Seminal work has demonstrated the potential of this approach in LVK, Euclid, HST, JWST, and CSST mock data, motivating the need for a dedicated software package to perform such analyses in practice. Here, we present the alpha-version of silmarel, the first software package designed to bridge these cosmic signals and enable us analysis of real LVK gravitational-wave binaries together with telescope observations from instruments like \textit{Euclid} or \textit{Hubble} Space Telescope, and the future of multimessenger binary black hole lensing.

Galaxies may suffer some starburst and quenched periods in their history due to e.g. galaxy mergers and feedback. However, semi-numerical simulations of the Epoch of Reionization (EoR) typically do not accurately model the effects of the star formation history (SFH) of galaxies. Keeping the same total ionizing photon budget from galaxies, we investigate how the ionization and heating of the Intergalactic Medium (IGM), as well as the associated 21-cm signal during the EoR, depends on the variations in the modeling of the SFH of galaxies. We adopt the Jiutian-300 N-body dark matter simulation and the semi-analytic model L-Galaxies 2020 to model galaxy formation. Using the galaxy catalog from L-Galaxies 2020 as input, we post-process the Jiutian-300 density field with the one-dimensional radiative transfer code Grizzly to model the reionization process and the 21-cm signal. We find that the ionized regions produced by galaxies with a SFH derived from L-Galaxies 2020 are slightly larger and warmer than the ones obtained with a constant SFR. For a fixed stellar mass, galaxies produce smaller ionized regions with increasing stellar mass weighted stellar age $\tau_{\rm age}$. This results in a different topology and timing of the IGM ionization and heating obtained from Grizzly. The SFH of galaxies is highly dependent on $\tau_{\rm age}$ and redshift. Different models of the galactic SFH affect the gas heating and ionizing processes during the EoR, and as a consequence also the 21-cm global signal and power spectrum.

We present the first systematic study of neutrino emissions from massive stars, continuously tracking the late evolutionary stages through the early core-collapse supernova phase. Using progenitor and supernova models, we analyze the neutrino luminosities and spectra for progenitors with initial masses of 10--40~$M_\odot$. Our systematic analysis reveals that the compactness parameter ($\xi_{2.5}$) and carbon-oxygen core mass ($M_{\text{CO}}$) exhibit strong correlations with neutrino emission. In the pre-supernova phase, the time-integrated number of neutrinos correlates with $\xi_{2.5}$ when integrated over the final day and with $M_{\text{CO}}$ for longer durations. For the early supernova phase ($<200$ ms post-bounce), the neutrino properties are relatively insensitive to the specific stellar evolution code used, allowing for a reliable extraction of physical correlations. We confirm that the neutrino emission features, including the electron neutrino burst properties and accretion-powered luminosity of other species, reflect the progenitor's compactness. An evaluation of the observational feasibility for a nearby progenitor using a False Alarm Rate approach suggests that these correlations can persist even under practical detection conditions. Such a joint analysis of both phases provides complementary constraints on the internal structure. All calculated time-series data will be made publicly available.

We present a trade study of possible ultra-deep surveys with the Nancy Grace Roman Space Telescope, optimizing the depth-area-filter parameter space for high-redshift galaxy science. Using a mock galaxy catalog derived from a 2 sq. degree lightcone created using the Santa Cruz semi-analytic model and populated with over 7.6 million galaxies at 0<z<10 with M_UV < -15, with realistic clustering and synthetic photometry, we evaluate sixteen 500-hour survey configurations spanning 0.28-2 sq. degrees and four filter combinations. We demonstrate that even a single Roman pointing dramatically reduces cosmic variance compared to HST-like observations, more faithfully recovering the true UV luminosity function. For each survey configuration, we explore photometric redshift recovery, sample contamination, and measurements of the rest-UV luminosity function and non-ionizing UV luminosity density across four redshift bins at z~6-9. We find that inclusion of the R062 filter is essential for studies at z~5-6, reducing sample contamination from nearly 100% to negligible levels and recovering the bright end of the luminosity function. The F184 filter improves galaxy recovery at z>9 and is critical for stellar contamination removal at all redshifts. Based on these results, we recommend that a Roman ultra-deep survey cover at least two Roman pointings (0.56 sq. degrees) with all six filters (R062, Z087, Y106, J129, H158, F184), reducing uncertainties on the rest-UV luminosity density by factors of 2-4 relative to the deepest existing JWST programs. Building off of the Deep Tier of the High Latitude Time Domain Survey to add depth and filter coverage to existing (or planned) observations is an excellent option.

Aims. We investigated the transport of solar energetic particles (SEPs) during the relativistic widespread event of 28 October 2021, quantifying the role of parallel and perpendicular diffusion and constraining the spatial extent of the injection region. Methods. We employed inverse modeling of particle focused transport and 2D numerical simulations including cross-field diffusion. Multi-spacecraft observations from STEREO-A, Solar Orbiter, and near-Earth spacecraft are used to reproduce particle intensity profiles and anisotropies across a wide range of electron and proton energies. Simulated flux profiles are compared across different heliolongitudes to derive consistent transport parameters. Results. The analysis yields parallel mean free paths within or slightly above the Palmer consensus range, and perpendicular mean free paths that correspond to $\sim 1$--$3\%$ of parallel for electrons and $\sim 5$--$10\%$ for protons. The injection region is found to be relatively narrow ($\leq 20^\circ$), and decreasing with particle rigidity. Multipoint simulations indicate that the observed flux and anisotropy profiles can only be reproduced by a narrow injection region and significant cross-field diffusion. Electron and proton release times align well with the parent X1.0 flare and associated coronal mass injection (CME) onset, indicating that a compact acceleration region coupled with efficient interplanetary diffusion governed the event's broad spatial extent.

JWST can pierce through dusty molecular clouds to study the early stages of star formation, where young star clusters are actively driving stellar feedback and still emerging from their natal cloud. We present a first look of the JWST/NIRSpec multiplex spectroscopy observations acquired by the Feedback in Emerging extrAgalactic Star clusTers (FEAST) program for the nearby spiral galaxy NGC628. We showcase JWST's ability to resolve the spectral properties of emerging young star clusters (eYSCs) and their immediate interstellar medium (ISM) by focusing on a bright star-forming complex ($0.5\times0.5~\mathrm{kpc}^2$) in the northern spiral arm as a science proof-of-concept. The eYSC spectra are rich in ionized gas (from HII regions), as well as warm H$_2$ and polycyclic aromatic hydrocarbon (PAH) emission from photodissociation regions (PDRs), consistent with young star formation. $\mathrm{Pa}\alpha$ equivalent widths and H/He ionizing photon fluxes both indicate the presence of hot, young massive stars (O8.5V-O8V), consistent with photometry SED estimates. The ionized gas is highly correlated with H$_2$ and PAH emission, suggesting that the PDR morphology evolves as clusters emerge from their natal cloud. We find a photoionization-dominated regime from independent line diagnostics, with little contribution from Supernovae-driven shocks, highlighting the importance of pre-Supernovae feedback when massive stars are present. This pilot study showcases how JWST's multiplex spectroscopy mode can disentangle the mechanisms present in the youngest stages of star formation for the first time outside the Local Group.

Quantifying the timescales of star cluster emergence from their natal clouds remains one of the main challenges in our understanding of the star formation process. These timescales are fundamental measurements of the star formation cycle within galaxies, yet they are difficult to constrain due to the complex interplay between stellar feedback and star formation across a vast range of physical scales. Here we present HST and JWST observations of thousands of young star clusters in four nearby galaxies (M51, M83, NGC 628, and NGC 4449). A substantial fraction of these clusters are still embedded within their natal gas and remain invisible at optical wavelengths. We constrain their emergence process by measuring the timescales required to disperse the surrounding material. We find a strong correlation between dispersal timescale and cluster stellar mass, with massive clusters emerging more rapidly than their lower mass counterparts. This is a critical constraint on simulations of star formation and stellar feedback, which struggle to fully reproduce the formation and emergence of star clusters. Our results emphasize the central role of massive clusters in driving the escape of ionizing radiation into the galactic medium. Finally, they impose important limitations to the time available for planet formation in massive cluster environments where disks get exposed to UV irradiation and further gas infall is shut off.

Recent models and simulations of cluster formation within molecular clumps consider multi-scale, hierarchical accretion, which leads to clump mass growth over time. This mode of mass accumulation could have implications regarding the evolution of observable properties such as mass and radius, bringing into question the interpretation of commonly cited thresholds for high-mass star formation. In this paper, we use the conveyor belt model of cluster formation to create synthetic cores/clumps and derive physical and observational properties. We show that while this model successfully predicts many observed trends, modifications are required to match properties of high-mass prestellar clumps. When the model clumps are observationally classified as intermediate- or high-mass star-forming, the threshold delineating these two groups agrees with those found in the literature; however, results show that high-mass clumps at early evolutionary stages can be misclassified using standard surface density thresholds. Our logistic regression analysis reveals the quantity of material to ever enter a star-forming region is the most important factor in differentiating intermediate- and high-mass star-forming regions. This implies observations characterising the environment surrounding star-forming regions are crucial, especially at early evolutionary stages.

Polaris is a highly unusual Cepheid with observed properties that are difficult to reconcile with stellar evolutionary models. Since the initial detection of Polaris' magnetic field in 2020, we have conducted a magnetic monitoring campaign with the ESPaDOnS spectropolarimeter at the Canada-France-Hawaii Telescope. We compute Stokes $V$ least-squares deconvolution profiles and measure the associated mean longitudinal magnetic field strengths $\langle B_{z}\rangle$. The surface magnetic field has remained remarkably stable over five years of observations, with $\langle B_{z}\rangle$ varying between approximately $-3$ G and $+0.6$ G. From the periodic modulation of $\langle B_{z}\rangle$ we infer a stellar rotation period of $P_{\mathrm{rot}}=100.29\pm0.19$ days. This is the first direct measurement of $P_{\mathrm{rot}}$ for a classical Cepheid. Previous interferometric radius measurements and $P_{\mathrm{rot}}$ imply an equatorial rotation velocity of $v_{\mathrm{eq}}=23.3\pm0.2$ km s$^{-1}$. We set a conservative upper bound on the projected equatorial rotational velocity of $v_{\mathrm{eq}}\sin i_{\star} < 13.5$ km s$^{-1}$ and constrain the stellar inclination angle to be $i_{\star}<37^{\circ}$. Using the previously determined orbital solution, we find a high likelihood of a strong spin-orbit misalignment. We determine the lower bound on the obliquity angle between the stellar rotation and orbital axes to be $\beta>18.7^{\circ}$ at 99% confidence. We discuss the challenges in interpreting the origin and properties of the surface magnetic field in the context of Polaris' uncertain evolutionary history and the merger hypothesis.

The capability of reconstructing the past star formation history of dwarf elliptical galaxies out of the Local Volume relies on modelling bright stellar populations currently evolving through the red giant branch (RGB) and the asymptotic giant branch (AGB) phases. Recent studies proposed the use of the relative fractions of RGB and AGB stars populating specific boxes in the observational colour-magnitude plane to infer the epoch within which 90\% of the stellar population of the galaxy formed (T90). We aim at understanding the physical process of stellar evolution that are constrained by the relationship between the relative fraction of AGB and RGB stars of dwarf galaxies and the T90 epoch. We use updated stellar models that include the description of dust formation in the wind, to undertake a population synthesis approach, to allow monitoring the variation of the NAGB/NRGB ratio with time. The effects of some specific ingredients, such as the mass loss experienced by low-mass stars during the RGB phase, and the details of the time variation of the star formation rate, are extensively explored and tested against data. The mass lost by low-mass stars during the RGB evolution proves the most relevant ingredients affecting the time variation of NAGB/NRGB: at metallicities ~ 1/10 solar, a mass loss ~ 0.25Msun is required to reproduce the observations. This analysis allows to derive a relationship between NAGB/NRGB and T90, with a ~ 1 Gyr uncertainty on T90.

The advent of high-precision Gaia parallaxes for Milky Way Cepheids enables per cent-level calibration of the local distance ladder and $H_0$. We revisit the Milky Way Cepheid calibration from Gaia EDR3 parallaxes using a fully forward-modelled Bayesian framework that simultaneously infers the period--luminosity relation, the Gaia parallax zero-point offset, and individual stellar distances while explicitly incorporating the disk geometry of the Galaxy through the distance prior and the selection functions specified in two distinct HST SH0ES campaigns. We derive an analytic treatment of the detection probability that accounts for magnitude, parallax, period, and extinction cuts and reduces the selection treatment to a tractable integral over distance and sky position. Posterior predictive checks show that this generative model matches well the observed distributions of parallaxes, magnitudes, and periods. Modelling Galactic structure and survey truncation self-consistently in a Bayesian framework yields period--luminosity parameters that agree with the SH0ES maximum-likelihood values at the ${<}0.5\,\sigma$ level, a consequence, we show, of the small intrinsic scatter of the Cepheid period--luminosity relation. Adopting, as recently advocated, a uniform-in-volume prior without simultaneously accounting for selection leads to a ${\sim}\,0.05~\mathrm{mag}$ bias in the period--luminosity zero-point and posterior predictive distributions incompatible with the observed data; this shift is mostly driven by the omission of the selection model. A consistent Bayesian treatment of Galactic structure and selection effects reinforces the local distance-ladder determination of $H_0$, and hence the Hubble tension with early-Universe inferences.

The One-hundred-deg^2 DECam Imaging in Narrowbands (ODIN) survey is conducting the widest-field deep narrow-band imaging of the equatorial and southern skies. ODIN uses three custom-built narrow-band (NB) filters that sample Lya-emitting galaxies (LAEs) within thin cosmic slices centered at z=2.4, 3.1, and 4.5. In this work, we utilize extensive DESI spectroscopy of ODIN-selected galaxies in the COSMOS and XMM-LSS fields to validate our LAE selection. 2-4 hr exposures with DESI yielded redshift confirmation of 3,075 ODIN LAE candidates with NB magnitudes brighter than 26~mag. Restricting to objects that yield high-confidence redshifts, the confirmation rates are (93, 96, 92)% at z=(2.4, 3.1, 4.5). The primary contaminants consist of active galactic nuclei at the expected Lya redshift range and lower redshifts (C IV, C III]), with the remainder being star-forming galaxies ([O II] and [O III]). We find minimal contamination from [O II] emitters in our sample (<~1%), implying that our REW>20 A narrow-band excess photometry requirement is sufficient to remove them.

Recent studies have uncovered a rare population of super-massive (M* > 1e11 Msun) star-forming spiral galaxies, Super Spiral Galaxies (SSGs), whose existence challenges classical quenching scenarios. We investigate the resolved star-forming and molecular-gas properties of UGC 8179 (z=0.052, log(M*/Msun)=11.62) and assess whether its local star formation (SF) follows the same physical processes as typical Star-Forming Main Sequence (SFMS) spirals. We combined the first NOEMA CO(1-0) interferometric observations of an SSG with pixel-by-pixel SED fitting, based on archival UV-to-mid-IR imaging. Our 3"x3" pixel maps provide resolved measurements of M*, SFR and molecular gas surface densities across its extended disc. UGC 8179 hosts a massive rotating molecular gas reservoir of M_H2 = 1.02 1e10 Msun, yielding a standard molecular gas fraction, with typical depletion time \sim 1 Gyr in the observed region, despite its extreme mass. We derived lower limits of log(fmol) > -1.61 \pm 0.06 and log(tdep) > -8.82 \pm 0.13 at the scale of the galaxy. The large spatial extent of UGC 8179 enables us to probe low surface-density regimes hardly accessible in nearby disks (\Sigma* < 1e7 Msun / kpc2 ; \Sigma_SFR < 1e-3.5 Msun/yr/kpc2). All three resolved scaling relations (rSFMS, rKS and rMGMS) are well defined. The rKS slope (0.87 \pm 0.09) is broadly consistent with unity, indicating standard local SF processes. The rSFMS shows a shallower global slope (0.80 \pm 0.02) due to a central suppression in sSFR (~ -0.5 dex). This break suggests the influence of a bulge, driving a transition to a more dynamically regulated SF regime in the inner disc. UGC 8179 provides evidence that SSGs can sustain standard local SF processes while exhibiting central dynamical regulation at high stellar surface densities.

We present a methodology for acquiring and reducing transiting exoplanet light curves obtained with the OPTICAM instrument in the Observatorio Astronómico Nacional en la Sierra de San Pedro Mártir (OAN-SPM). The OPTICAM sCMOS detectors generate significant warm pixels at exposures $\geq$10s, affecting both science and calibration frames. These warm pixels are not removed by standard dark subtraction because they vary unpredictably from frame to frame. We evaluate six pre-processing methods applied to science and calibration images using the transit of TOI-7149~b observed in g$^\prime$r$^\prime$i$^\prime$. A median filter with a 3$\times$3-pixel window minimizes the effect of warm pixels without affecting stellar signals. This median filter best reduces dispersion and red noise in the light curves when stellar peak counts are close to the dark current level. The improvement is less significant when the stellar peak is several thousand counts above the dark current level. We fit a multiband transit model to the light curves, measuring photometric precision, correlated noise, and retrieved planetary parameters. The transit model fitted to the light curves with pre-processing using a 3$\times$3-median filter achieves the highest Bayesian evidence. Thus, it is our recommended method for correcting warm pixels. Finally, we present a reduction pipeline that combines Python modules (PROFE) and AstroImageJ to implement our proposed method for OAN-SPM 2.1m+OPTICAM transiting planet observations.

We present a comprehensive polarimetric study of 26 nearby molecular clouds in four far-infrared bands (53 $\mu$m to 214 $\mu$m) using 52 archival SOFIA/HAWC+ datasets. Far-infrared dust polarization observations probe the plane-of-sky magnetic field. To investigate scale-dependent trends, we group the molecular clouds by distance and analyze the data at common angular ($25''$) and common physical (0.052 pc and 0.32 pc) resolutions. The two shorter wavelengths are more impacted by smoothing, exhibiting a larger decrease in percent polarization. We analyze the polarization spectrum -- the polarization fraction as a function of wavelength -- and find that it depends more strongly on column density than dust temperature. We find a "falling" spectrum at the 0.052 pc resolution, but find a "flat" spectrum at the 0.32 pc resolution, suggesting that resolution plays an important role in the observed polarization spectra. We propose that warm dust grain emission in small-scale structures ($\lesssim$ 0.1 pc) traces different magnetic field geometries only resolved in our close regime data. There is no preferred magnetic field orientation across our data, which suggests that the magnetic field in our $\sim$ parsec scale regions is decoupled from the large-scale field that is primarily parallel to the Galactic plane. The relationship between percent polarization and column density varies between clouds, but the correlation between percent polarization and angular dispersion is consistent across regions. This compendium of dust polarization maps highlights the value of observing at multiple far-infrared wavelengths and will enable additional population-level studies of magnetic fields and dust across star-forming environments.

In the late Universe, and on cosmological scales, dark matter is conventionally assumed to be collisionless, as a consequence of the strong existing bounds on dark matter interactions at the Cosmic Microwave Background last-scattering surface. Challenging this lore, here we show that dark matter interactions can be naturally weak at early times, but then grow to observationally relevant strengths at very late times, even significantly after reionization. This is realized if dark matter recouples to a dark radiation species in the range of redshifts probed by the current generation of galaxy surveys. We systematically study, for the first time, the phenomenology of this dark matter recoupling scenario. A combination of Cosmic Microwave Background and Baryon Acoustic Oscillation data show that the interaction needs to be weak at present, if the entirety of dark matter couples to dark radiation. From a complementary perspective, a 4% fraction of dark matter could still be strongly interacting today. Implications for a microscopic model realizing the recoupling dynamics are discussed.

Observations of Type Ia supernovae (SNIa), baryon acoustic oscillations (BAO), and the cosmic microwave background (CMB), which probe the late-, intermediate-, and early-universe epochs, respectively, provide complementary constraints on the expansion history of the Universe. In this work, we forecast constraints on dark energy and other extensions to the standard cosmological model by combining the SNIa sample expected from the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST), data from current and forthcoming CMB surveys, and BAO measurements from the Dark Energy Spectroscopic Instrument (DESI). For the CMB, we use temperature, polarization, and lensing power spectra ($TT/EE/TE/\phi\phi$) from South Pole Telescope, the planned Advanced Simons Observatory, and a CMB-S4-like experiment. We derive constraints on $\Lambda {\rm CDM}$ and its extensions involving the dark energy equation of state parameters $(w_{0}, w_{a})$ and the sum of neutrino masses $\sum m_{\nu}$, using a Markov Chain Monte Carlo (MCMC) sampling framework. We find that the LSST Year-3 SNIa sample can improve upon the DES Year-5 dark energy constraints by a factor of $\times2-\times2.5$, with the gains driven primarily by the significantly higher SNIa density in the LSST sample. Similarly, DESI-DR3 shows up to a $\times1.8$ improvement on dark energy parameters over DR2, driven largely by the substantial increase in low-redshift sample. Combining CMB with LSST-Y3-SNIa and DESI-DR3-BAO yields $\sigma(w_{0}) = 0.028$ and $\sigma(w_{a}) = 0.11$ for $w_{0} w_{a} {\rm CDM}$ cosmology with the results being largely independent of the CMB dataset. The constraints weaken by 10%-30% when freeing $\sum m_{\nu}$ and spatial curvature. Moreover, the joint analysis of the three datasets can enable a $2-3\sigma$ detection of $\sum m_{\nu}$.

We present measurements of black hole (BH) properties of 861 Type-1 active galactic nuclei (AGNs) in the North Ecliptic Pole (NEP)-Wide field. These AGNs are detected in both optical and mid-infrared (MIR) surveys and are identified as Type-1 AGNs in optical spectroscopic surveys. By performing spectral energy distribution (SED) and line fitting, we obtained their MIR continuum luminosities ($L_{\rm MIR}$) as well as full width at half maximum (FWHM) values for the \ion{C}{4}, \ion{Mg}{2}, H$\beta$, and H$\alpha$ lines. Using these measurements, we derived bolometric luminosities ($10^{43.20}$--$10^{47.27}~{\rm erg~s^{-1}}$), BH masses ($10^{7.29}$--$10^{9.67}$\,$M_{\odot}$), and Eddington ratios ($10^{-2.74}$--$10^{-0.08}$) for $\sim$450 objects over a wide redshift range ($z=0.09$--$4.71$). The use of $L_{\rm MIR}$ and FWHM values effectively alleviates the effects of dust extinction, enabling reliable estimates of BH properties even for dust-obscured AGNs. Moreover, we find that 34\,\% of the Type-1 AGNs in the NEP-Wide field are dust-obscured, and that their bolometric luminosities can be significantly underestimated without proper dust extinction correction. Our relatively extinction-free BH property estimates can (i) be combined with multi-wavelength data in the NEP-Wide field to facilitate diverse studies of AGN environments, number densities, host galaxies, and related topics, and (ii) serve as fiducial estimates for SPHEREx and other upcoming infrared (IR) spectroscopic missions covering the NEP-Wide field.

We investigate elastic scattering by a compact, horizonless body in curved spacetime, considering a massless scalar wave incident on a static, spherically symmetric, uniform-density star of radius $R$ and mass $M$ with a Schwarzschild exterior. We introduce an exact Debye-series decomposition of the scattering matrix, in the spirit of Debye expansions in Mie scattering. This decomposition separates direct surface reflection from contributions involving transmission into the interior and subsequent propagation, and admits a natural trajectory interpretation. We then determine the associated Regge-Debye pole spectrum in the complex angular-momentum plane. For neutron-star-like tenuities ($R>3M$), the spectrum exhibits two pole families: a surface-wave branch associated with the surface matching condition and a broad-resonance branch associated with the interior regularity condition. For ultracompact objects ($R<3M$), the surface-wave branch persists, while the interior-resonance sector splits into broad- and narrow-resonance branches. We next reconstruct the scattering amplitude from the Debye partial-wave contributions and find excellent agreement with direct partial-wave calculations. Finally, we develop complex angular-momentum representations order by order in the Debye series, making explicit how the pole families and non-pole sectors contribute to each Debye term. In the neutron-star-like regime, we find a genuine competition between Regge-Debye pole sums and branch-cut contributions, and show that, at high frequency, the rainbow-like enhancement already arises from the first interior-transmission contribution and is dominated by the interior-resonance Regge-Debye poles. By contrast, in the ultracompact regime, the Debye amplitudes are overwhelmingly pole dominated.

We explore the aggregate effect of binary systems on the Milky Way's dark matter (DM) velocity distribution with Monte Carlo simulations. Through gravitational interactions with binaries, transiting DM particles can gain substantial energy. We analyze this mechanism across a range of galactic binaries, and find it to be most effective for double black holes, where ejection speeds can reach $\sim 2000 \ \rm km/s$ while attaining a large ejection rate. We assess the expected binary-boosted DM flux from synthetic populations of black hole binaries in the galaxy, and show direct detection experiments can be sensitive to it. In particular, we demonstrate that large noble liquid detectors such as Lux-Zeplin and PandaX-4T can extend their mass sensitivity down to the sub-GeV scale, and potentially become competitive with other lower-threshold experiments when the full galactic black hole binary population is taken into account. This boosting mechanism, being gravitational in nature, is largely model- and mass-independent.

The quasinormal modes of black holes (BHs) in the large-angular-momentum limit can be computed within the eikonal approximation. This approximation is often extrapolated to low angular momentum to obtain a rough estimate of the dominant ringdown modes. Although approximate, this approach is particularly convenient in theories beyond general relativity with intricate dynamics, or for phenomenological metrics that lack an underlying fundamental theory. Here we explore a complementary approximate strategy: we compute exactly the quasinormal modes of a test scalar field propagating on the BH background and use their \emph{deviations} from the general-relativity predictions as a proxy for the corresponding corrections to the gravitational quasinormal modes. For Kerr-Newman and Einstein-scalar-Gauss-Bonnet BHs, we show that this method reproduces the exact corrections (including the coupling among different degrees of freedom) within tens of percent, an accuracy that is adequate as long as ringdown measurements remain at the percent level. Furthermore, this method is typically comparable to, or more accurate than, the eikonal approximation. We then apply the same strategy to phenomenological metrics commonly employed in tests of gravity using BH imaging. By computing scalar quasinormal modes in a large family of these metrics for the first time, we find that current ringdown constraints are comparable to, and in some cases more stringent than, those derived from BH shadow observations, while also providing complementary bounds on sectors that would otherwise be inaccessible.

Cosmological observables of the primordial universe are encoded in the late-time field-theoretic wavefunction. For shift-symmetric scalars in de Sitter, a good approximation for many inflationary models, the wavefunction must be purely real at tree-level. This property is violated by a quantum anomaly in the process of renormalization. As a result, we show that the imaginary part of the wavefunction is fixed by its dependence on the renormalization scale to all loop orders in perturbation theory. This follows from unitarity, locality, dilation isometry and a Bunch-Davies state. The compact relation we uncover for the wavefunction implies an infinite set of relations among correlators of massless fields and their conjugate momenta, which we exemplify at one-loop order.

We study axion-neutrino interactions in neutrino-mass extensions of the Standard Model, focusing on the Type-I and inverse seesaw. In these frameworks the effective coupling $g_{a\nu}$ is tied to the axion scale and can be constrained using existing astrophysical limits on axion couplings to electrons. We then estimate the impact of axion-mediated scattering on neutrino propagation in two benchmarks: resonant interactions with the C$\nu$B and scattering on axion dark matter. In the parameter space allowed by current bounds, the resulting optical depths are extremely small, implying no observable signatures with present sensitivities.

Beyond solving the hierarchy problem, classically conformal (CC) theories naturally accommodate dark matter (DM). In this work, we explore the CC $SU(2)_X$ gauge theory with a triplet dark scalar, uncovering three distinct DM scenarios: WIMP, supercooled DM, and monopole. The production mechanisms are strongly influenced by the CC model's unique first-order phase transition evolution history, which differs significantly from those in non-conformal models. We obtain the viable parameter space for each scenario and investigate the current constraints and future sensitivities at terrestrial experiments and gravitational wave observatories.

Maximizing pre-merger warning times in gravitational-wave searches requires minimizing algorithmic latency. While current pipelines typically rely on truncated linear-phase filters, minimum-phase whitening offers a zero-latency alternative that eliminates the acausal look-ahead buffer. However, this causal approach exposes the analysis to spectral drift, where the whitening operator applied to live data diverges from the static template bank, creating a functional perturbation of the matched-filter metric. We develop a perturbative framework generalizing the Cutler-Vallisneri formalism to address these metric errors, deriving analytic expressions for the resulting timing, phase, and SNR biases. Validated against exact stationary-phase models and numerical injections, these corrections achieve $<1\%$ error. Applying this framework to GWTC-4.0 events with realistic 1-week power spectral density (PSD) lags, we find that uncorrected drift induces severe systematics: detector-pair timing biases exceeding $200 \mu$s, phase shifts up to 0.2 rad, and sky-localization errors of $5^{\circ}-10^{\circ}$. Additionally, we observe a median signal-to-noise ratio (SNR) loss of $3-5\%$, with outliers exceeding $8\%$. These results demonstrate that while minimum-phase whitening maximizes the early-warning window, analytic drift corrections are essential to maintain detection volume and pointing accuracy in future observing runs.

The events detected by the LIGO Virgo KAGRA collaboration over a period of 10 years have yielded a treasure trove of signals from compact binary coalescences. None of these events have shown a confident signature of eccentricity. With upgrades to the existing network and potential next generation gravitational wave detectors, we will be able to see much further into the universe increasing the likelihood of detecting eccentric systems. We improve upon the phenomenological approach of providing eccentricity constraints using an effective chirp mass model in the time frequency domain. We introduce an improved pixel collection method along with a likelihood based sampling approach inspired by Bayesian parameter estimation. Our approach constructs a likelihood from the product of energies collected across different eccentric harmonics in the time frequency representation. This formulation enables coarse but meaningful constraints on orbital eccentricity. Additionally, we incorporate information from the energy ratios between eccentric harmonics, further refining the eccentricity estimates. We test our approach on 500 non spinning equal mass eccentric systems and demonstrate that we can constrain the eccentricity within 0.2 around the true value. Moreover, our approach can deliver these constraints in 5 minutes on a machine with 50 cores. These results demonstrate that our phenomenological approach provides fast and reasonably accurate eccentricity estimates, making it a promising tool for rapid gravitational wave data analysis.

The QCD Equation of State with $N_f=3$ massless quark flavours is determined non-perturbatively over a broad range of temperatures, extending from the electroweak scale down to 3 GeV, and smoothly connecting to the low-temperature regime. The comparison with perturbative predictions shows that, even at temperatures approaching the electroweak scale, the Equation of State can be accurately described only by adding terms beyond the known perturbative series, including non-perturbative contributions. The strategy that allows this investigation in the previously unexplored high-temperature regime combines shifted boundary conditions with a determination of the lines of constant physics based on the running of a non-perturbatively defined renormalized coupling. This methodology is general and can be applied to QCD with four or five massive quark flavours.

Gravitational wave searches rely on a combination of methods, including matched filtering, coherent analyses, and more recent machine learning based pipelines. For compact binary coalescences, where signals originate from the relativistic dynamics of compact objects, matched filtering remains a central element, but its computational cost will increase substantially with the data volumes and parameter-space coverage required by next-generation interferometers such as the Einstein Telescope. Developing complementary strategies that reduce computational load while preserving detection performance is therefore essential. We investigate a hybrid approach that combines matched-filtering concepts with Convolutional Neural Networks, enabling efficient signal searches without relying on the usual $\chi^2$ rejection test. Using simulated data sets that include injected signals in Gaussian noise, transient noise, and physical effects not represented in template bank, such as eccentricity, precession and higher-order modes, we show that the method achieves a detection efficiency comparable to a standard matched-filtering search while offering a more resource efficient pipeline. These results indicate that deep learning assisted searches can support sustainable gravitational-wave data analysis in future detector eras.

For light and massless scalar fields, cosmological correlation functions suffer from infrared divergences and secular logarithms. Soft de Sitter Effective Theory (SdSET) has been proposed by Cohen and Green as the effective description of the non-trivial dynamics of long-wavelength modes $k_{\rm phys} < H$ in de Sitter space, which is responsible for the infrared and late-time logarithms, and as a systematic extension of the stochastic approach. In this article, we construct SdSET in dimensional regularisation, including an initial-condition functional. We demonstrate by examples that renormalisation and matching works as for flat-space effective field theories. Adopting massless $\kappa \phi^4$ theory as the UV theory, we match the tree-level trispectrum and six-point function, and the one-loop power spectrum to SdSET, verifying explicitly that SdSET is the appropriate effective field theory for the quantum dynamics of superhorizon modes.

This work presents the design and performance characterization of the optical calibration systems produced for the Pacific Ocean Neutrino Experiment (P-ONE). These include novel light-pulse driver circuitry based on gallium nitride field-effect transistor technology and its application to directional and isotropic, self-monitoring optical calibration instruments. A total of 330 directional light pulsers and two isotropic, 17-inch calibration modules (P-CALs) were produced for the first P-ONE line. We present the designs and performance of both the directional and isotropic calibration devices and perform detailed optical characterizations of both full-production batches. In a wavelength range of $365-520\,$nm, our developed driver circuits achieve emission intensities up to $10^{11}\,$photons and pulse widths as small as $1.4\,$ns, respectively. Light-pulse drivers and self-monitoring electronics in the P-CAL were characterized using the same experimental setup, and the instrument's optical-isotropy design was optimized in combination with a dedicated GEANT4-based simulation framework. The optimized P-CAL achieves a simulated isotropy grade of $1.00 \pm 0.01$ across the entire $4 \pi$ solid angle range. These simulation investigations were explicitly confirmed by dedicated measurements in both air and water using two independent experimental setups, and we report the results. With this, a detailed performance estimate for deployed P-CAL modules in P-ONE was possible.

Extreme mass-ratio inspirals (EMRIs) are long-duration gravitational-wave sources in which a compact object gradually spirals into a massive black hole. Their formation is governed by the interplay between stochastic angular-momentum diffusion driven by two-body relaxation and the dissipative evolution caused by gravitational-wave emission, with the loss-cone boundary deciding whether an object undergoes an inspiral or a direct plunge. Building on this physical picture, we construct a relativistically self-consistent analytic framework for estimating EMRI event rates. In Schwarzschild spacetime, we generalize the standard loss-cone angular momentum to an energy-dependent quantity and revise the plunge pericenter by using the minimum stable radius derived from general relativity. Relative to the Newtonian treatment, we show that incorporating these relativistic effects increases the predicted EMRI rates by roughly a factor of 8. This enhancement becomes more pronounced for shallower stellar density profiles and is insensitive to the mass of the central massive black hole, which emphasizes that relativistic effects are essential for EMRI rate estimations that are relevant for space-based gravitational-wave detectors, such as LISA and Taiji.

We propose a novel strategy to probe feebly-interacting particles (FIPs) by exploiting the dense, confined circumstellar medium (CSM) surrounding core-collapse supernovae (CCSNe). FIPs produced in the proto-neutron star can deposit substantial visible energy into the CSM via decay prior to the shock breakout from the progenitor star. This energy injection heats and ionizes the CSM, establishing a FIP-induced photosphere that generates distinctive precursor blackbody emission. Using early-time observations of SN 2023ixf, we translate the non-detection of excessive precursor luminosity into stringent new constraints on MeV-scale dark photons as an exemplary model. Our results significantly extend existing CCSN bounds and exclude previously unexplored regions of parameter space. We further demonstrate that the FIP-induced dust sublimation offers robust diagnostics for future Galactic SNe, opening a new avenue to explore the dark sector.

Observational evidence, together with practical computations and modeling, supports a Euclidean spatial sector in the current cosmological model based on the FLRW metric. This, however, would imply that the total amount of matter and energy immediately after the Big Bang must have been infinite, an implication that could only be avoided through a transition from a closed to an open universe, a process forbidden in standard FLRW models. In this article, we investigate the spacetimes resulting from promoting the spatial curvature $k$ in FLRW spacetimes to a time-dependent function, $k \to k(t)$, allowing it to change sign and thereby allowing changes in the topology of the constant-$t$ slices. Although previously dismissed due to a classical theorem by Geroch, such transitions are shown to be consistent with global hyperbolicity when the comoving time is distinct from a Cauchy time, as recent work by one of the authors demonstrates. We construct three distinct geometries exhibiting this behavior using different representations of constant-curvature spaces. We analyze their global properties and identify mild conditions under which they remain globally hyperbolic. Furthermore, we characterize their Killing vectors, proving a general result for spherically symmetric spacetimes and compare them with known geometries in the literature.