Papers for Friday, Sep 26 2025

This paper presents UNAGI, a novel spacecraft mission developed by Spartan Space Systems, a student engineering team at San Jose State University, aiming for the first controlled landing on Jupiter's volcanically active moon Io. Inspired by the Japanese freshwater eel's agility, UNAGI employs an electrodynamic tether system that interacts with Jupiter's magnetic field to generate Lorentz forces, enabling dynamic modulation of the spacecraft's velocity without the need for traditional propellant. This system allows the spacecraft to precisely match Io's orbital velocity, similar to a surfer riding a wave. By optimizing tether current and orientation, UNAGI transitions from an outer Jovian insertion orbit to an orbit around Io, achieving a controlled landing for on-surface science operations. The landing is strategically timed, leveraging the gravitational influence of Jupiter and its moons to decelerate descent and mitigate impact forces. UNAGI leverages technologies from missions like Juno, JUICE, and Europa Clipper to ensure reliable operation in the challenging Jovian environment. The mission follows a phased approach, including cruise, orbital insertion, tether deployment, Jovian orbital operations, and final descent, with extensive risk mitigation through simulations and experimental validation. The concept supports rideshare integration on future NASA or ESA missions or a dedicated launch, emphasizing cost effectiveness and adaptability. UNAGI carries a scientific payload including infrared spectrometers, magnetometers, seismometers, and chromatographs, designed to probe Io's interior dynamics, volcanic activity, tectonic deformation, and magnetospheric interactions. This mission aims to advance understanding of Io's geophysical processes and Jupiter system dynamics, setting a new standard for deep space exploration of extreme environments.

Radio signals propagating through inhomogeneous plasma media deviate from their original paths, producing frequency-dependent magnification effects. In this paper, after reviewing the classical plasma-lensing theory, we have found a fundamental contradiction: the classical model assumes that the distribution of lensing plasma medium is related to the frequency-independent image position; however, our analysis demonstrates that both the image position ($\theta(\nu)$) and dispersion measure (DM$(\nu)$) are inherently frequency-dependent when signals traverse a structured plasma medium. We have been able to resolve this paradox by developing a framework that explicitly incorporates frequency-dependent dispersion measures (DMs) following power-law relationships ($\rm DM\propto \nu^\gamma$). Our analysis shows that the signal magnification decreases systematically with decreasing frequency, offering a plausible explanation for the frequency-dependent peak flux densities observed in fast radio bursts (FRBs), particularly in the case of the repeating FRB 180814.J0422+73. Our results suggest these FRBs could originate from the magnetized compact star magnetospheres. By considering these plasma-lensing effects on the sub-pulses of an FRB across different frequencies, we have the ability to more accurately investigate the intrinsic properties of FRBs via precise measurements of radio signals.

The rate at which giant planets accumulate solids and gas is a critical component of planet formation models, yet it is extremely challenging to predict from first principles. Characterizing the heavy element (everything other than hydrogen and helium) content of giant planets provides important clues about their provenance. Using thermal evolution models with updated H-He EOS and atmospheric boundary condition that varies with envelope metallicity, we quantify the bulk heavy element content of 147 warm ($< 1000$ K) giant planets with well-measured masses and radii, more than tripling the sample size studied in Thorngren et al. 2016. These measurements reveal that the population's heavy element mass follows the relation $M_{\rm Z} = M_{\rm core} + f_Z (M_{\rm p} - M_{\rm core})$, with $M_{\rm core} = 14.7^{+1.8}_{-1.6}$ Earth masses (M$_\oplus$), $f_Z = 0.09 \pm 0.01$, and an astrophysical scatter of $0.66 \pm 0.08 \times M_Z$. The classical core-accretion scenario ($Z_{\rm p} = 1$ at 10 M$_\oplus$ and $Z_{\rm p} = 0.5$ at 20 M$_\oplus$) is inconsistent with the population. At low planet masses ($<< 150$ M$_\oplus$), $M_{\rm Z} \sim M_{\rm core}$ and as a result, $Z_{\rm p} = M_{\rm Z} / M_{\rm p}$ declines linearly with $M_{\rm p}$. However, bulk metallicity does not continue to decline with planet mass and instead flattens out at $f_Z \sim 0.09$ ($\sim 7 \times$ solar metallicity). When normalized by stellar metallicity, $Z_{\rm p} / Z_\star$ flattens out at $3.3 \pm 0.5$ at high planet masses. This explicitly shows that giant planets continue to accrete material enriched in heavy elements during the gas accretion phase.

The evolution and structure of sub-Neptunes may be strongly influenced by interactions between the outer gaseous envelope of the planet and a surface magma ocean. However, given the wide variety of permissible interior structures of these planets, it is unclear whether conditions at the envelope-mantle boundary will always permit a molten silicate layer, or whether some sub-Neptunes might instead host a solid silicate surface. In this work, we use internal structure modeling to perform an extensive exploration of surface conditions within the sub-Neptune population across a range of bulk and atmospheric parameters. We find that a significant portion of the population may lack present-day magma oceans. In particular, planets with a high atmospheric mean molecular weight and large envelope mass fraction are likely to instead have a solid silicate surface, since the pressure at the envelope-mantle boundary is high enough that the silicates will be in solid post-perovskite phase. This result is particularly relevant given recent inferences of high-mean molecular weight atmospheres from JWST observations of several sub-Neptunes. We apply this approach to a number of sub-Neptunes with existing or upcoming JWST observations, and find that in almost all cases, a range of solutions exist which do not possess a present-day magma ocean. Our analysis provides critical context for interpreting sub-Neptunes and their atmospheres.

We study star formation over 12 Gyr using pop-cosmos, a generative model trained on 26-band photometry of 420,000 COSMOS2020 galaxies (IRAC Ch.1 $<26$). The model learns distributions over 16 SPS parameters via score-based diffusion, matching observed colours and magnitudes. We compute the star formation rate density (SFRD) to $z=3.5$ by directly integrating individual galaxy SFRs. The SFRD peaks at $z=1.3\pm0.1$, with peak value $0.08\pm0.01$ M$_{\odot}$ yr$^{-1}$ Mpc$^{-3}$. We classify star-forming (SF) and quiescent (Q) galaxies using specific SFR $<10^{-11}$ yr$^{-1}$, comparing with $NUVrJ$ colour selection. The sSFR criterion yields up to 20% smaller quiescent fractions across $0<z<3.5$, with $NUVrJ$-selected samples contaminated by galaxies with sSFR up to $10^{-9}$ yr$^{-1}$. Our sSFR-selected stellar mass function shows a negligible number density of low-mass ($<10^{9.5}$ M$_\odot$) Q galaxies at $z\sim1$, where colour-selection shows a prominent increase. Non-parametric star formation histories around the SFRD peak reveal distinct patterns: SF galaxies show gradually decreasing SFR correlations with lookback time ($r\sim1$ to $r\sim0$ over 13 Gyr), implying increasingly stochastic star formation toward early epochs. Q galaxies exhibit full correlation ($r>0.95$) during the most recent $\sim$300 Myr, then sharp decorrelation with earlier star-forming epochs, marking clear quenching transitions. Massive ($10<\log_{10}(M_*/$M$_{\odot})<11$) galaxies quench on a time-scale of $\sim1$ Gyr, with mass assembly concentrated in their first 3.5 Gyr. Finally, AGN activity (infrared luminosity) peaks as massive ($\sim10^{10.5}$ M$_\odot$) galaxies approach the transition between star-forming and quiescent states, declining sharply once quiescence is established. This provides evidence that AGN feedback operates in a critical regime during the $\sim1$ Gyr quenching transition.

Long period radio transients (LPTs) are periodic radio sources showing pulsed emission on timescales from minutes to hours. The underlying sources behind this emission are currently unclear. There are two leading candidates: neutron stars or white dwarfs. Neutron stars could emit at LPT timescales as magnetars, binaries, or precessing sources. White dwarfs on the other hand have only been observed to emit in radio as binary systems with companions that provide charged particles through their wind. A key distinction is that an optical counterpart is much more likely in the white dwarf scenario. GPM J1839-10 is an LPT with a radio period of 21 min for which the white dwarf scenario has been favoured, but no optical counterpart is confirmed. Using HiPERCAM, a high-speed multi-colour photometer that observes simultaneously in ugriz filters, we probe the existence of a white dwarf in GPM J1839-10. We do not directly detect a white dwarf, but cannot rule out its presence given the uncertain distance and reddening of GPM J1839-10. On the other hand, we find evidence in our data for periodic behaviour in harmonics of the radio period, as expected from the white dwarf scenario.

Metals enhance the cooling efficiency of molecular clouds, promoting fragmentation. Consequently, increasing the metallicity may boost the formation of low-mass stars. Within the integrated galaxy initial mass function (IGIMF) theory, this effect is empirically captured by a linear relation between the slope of the low-mass stellar IMF, $\alpha_1$, and the metal mass fraction, $Z$. This linear $\alpha_1$-$Z$ relation has been calibrated up to $\approx 2 \, Z_{\odot}$, though higher metallicity environments are known to exist. We show that if the linear $\alpha_1$-$Z$ relation extends to higher metallicities ($[Z] \gtrsim 0.5$), massive star formation is suppressed entirely. Alternatively, fragmentation efficiency may saturate beyond some metallicity threshold if gravitational collapse cascades rapidly enough. To model this behavior, we propose a logistic function describing the transition from metallicity-sensitive to metallicity-insensitive fragmentation regimes. We provide a user-friendly public code, pyIGIMF, which enables the instantaneous computation of the IGIMF theory with the logistic $\alpha_1$-$Z$ relation.

Weak gravitational lensing is a powerful probe of cosmology, with second-order shear statistics commonly used to constrain parameters such as the matter density $\Omega_\mathrm{m}$ and the clustering amplitude $S_8$. However, parameter degeneracies remain and can be reduced by including higher-order statistics such as the third-order aperture mass. To jointly analyse second- and third-order statistics, an accurate model of their cross-covariance is essential. We derive and validate a non-tomographic analytical model for the cross-covariance between second- and third-order aperture mass statistics. Analytical models are computationally efficient and enable cosmological parameter inference across a range of models, in contrast to numerical covariances derived from simulations or resampling, which are costly or biased. Our derivation is based on real-space estimators of the aperture mass. Substituting the Halofit power spectrum, BiHalofit bispectrum, and a halo-model tetraspectrum, we validate the model against numerical covariances from the $N$-body Scinet LIghtCone Simulations (SLICS) using shear catalogues and convergence maps. We perform a Markov chain Monte Carlo analysis with both analytical and numerical covariances for several filter scale combinations. The cross-covariance separates into three terms governed by the power spectrum, bispectrum, and tetraspectrum, with the latter dominating. The analytical model qualitatively reproduces simulations, though differences arise from modelling approximations and numerical evaluation. Analytical contours are systematically tighter, with a combined figure of merit 72% of the numerical case, rising to 80% when small-scale information is excluded. This work completes the analytical covariance framework for second- and third-order aperture mass statistics, enabling joint parameter inference without large simulation suites.

Recent efforts have extended our view of the number and properties of satellite galaxies beyond the Local Group firmly down to $\rm M_\star\sim 10^6 M_\odot$. A similarly complete view of the field dwarf population has lagged behind. Using the background galaxies sample from the Satellites Around Galactic Analogs (SAGA) Survey at $z<0.05$, we take inventory of the dwarf population down to $\rm M_\star \sim 5\times10^6 M_\odot$ using three metrics: the stellar mass function (SMF) as function of environment, the stellar-to-halo mass relation (SHMR) of dwarf galaxies inferred via abundance matching, and the quenched fraction of highly isolated dwarfs. We find that the low-mass SMF shape shows minimal environmental dependence, with the field dwarf SMF described by a low-mass power-law index of $\alpha_1=-1.44\pm0.09$ down to $\rm M_\star \sim 5\times10^6 M_\odot$, and that the quenched fraction of isolated dwarfs drops monotonically to $f_{q} \sim 10^{-3}$ at $\rm M_\star \sim \rm 10^{8.5} M_\odot$. Though slightly steeper than estimates from \HI{} kinematic measures, our inferred SHMR agrees with literature measurements of satellite systems, consistent with minimal environmental dependence of the SHMR in the probed mass range. Finally, although most contemporary cosmological simulations against which we compare accurately predict the \sagalocal{} SHMR, we find that big-box cosmological simulations largely over-predict isolated galaxy quenched fractions via a turnaround in $f_q(\rm M_\star)$ at $\rm 10^8\lesssim M_\star/M_\odot\lesssim 10^9$, underscoring the complexities in disentangling the drivers of galaxy formation and the need for systematic multidimensional observations of the dwarf population across environments.

We present measurements of stellar population properties of a newly discovered spectroscopically confirmed $z=11.10^{+0.11}_{-0.26}$, gravitationally lensed galaxy, using JWST NIRSpec PRISM spectroscopy and NIRCam imaging. The arc is highly magnified by the Bullet Cluster (magnification factor ${\mu}=14.0^{+6.2}_{-0.3}$. It contains three star-forming components of which one is barely resolved and two are unresolved, giving intrinsic sizes of $\lesssim 10pc$. The clumps also contain ~50% of the total stellar mass. The galaxy formed the majority of its stars ~150Myr ago (by z~14). The spectrum shows a pronounced damping wing, typical for galaxies deep in the reionisation era and indicating a neutral IGM at this line of sight. The intrinsic luminosity of the galaxy is $0.086^{+0.008}_{-0.030} L^*$ (with $L^*$ being the characteristic luminosity for this redshift), making it the lowest luminosity spectroscopically confirmed galaxy at $z>10$ discovered to date.

We study the stability and possible fates of Little Red Dots, under the stellar-only interpretation of their observational features. This is performed by a combination of analyzing the relevant timescales in their stellar dynamics and also, the application of recent numerical results on the evolution of the densest stellar systems. We study different scenarios for the evolution of Little Red Dots and conclude that in a fair fraction of those systems, the formation of a massive black hole by runaway collisions seems unavoidable, in all the possibilities studied within the stellar-only interpretation. We conclude that Little Red Dots are the most favourable known places to find a recently formed massive black hole seed, or in the process of formation, most probably formed directly in the supermassive range

Recent photometric surveys with JWST have revealed a significant population of mysterious objects with red colours, compact morphologies, frequent signs of active galactic nucleus (AGN) activity, and negligible X-ray emission. These 'Little Red Dots' (LRDs) have been explored through spectral and photometric studies, but their nature is still under debate. As part of the BlackTHUNDER survey, we have observed UNCOVER_20466, the second most distant LRD known (z=8.5), with the JWST/NIRSpec IFU. Previous JWST/NIRCam and JWST/NIRSpec MSA observations of this source revealed its LRD nature, as well as the presence of an AGN. Using our NIRSpec IFU data, we confirm that UNCOVER_20466 contains an overmassive black hole. However, our observed Balmer decrements imply negligible dust attenuation, resulting in a much lower Hbeta-based bolometric luminosity and Eddington luminosity (~10%) than previously found. Lyman-alpha emission is strongly detected, implying f_esc,Lya~30%. The extremely high [OIII]4363/Hgamma ratio is indicative of not only AGN photoionization and heating, but also extremely high densities (ne~10^7cm-3), suggesting that this black hole at such high redshift may be forming in an ultra-dense protogalaxy.

The ring and gap structures found in observed protoplanetary disks are often attributed to embedded gap-opening planets and typically modeled with simplified thermodynamics in the 2D, thin disk approximation. However, it has been shown that radiative cooling and meridional processes play key roles in planet-disk interaction, though their computational cost has limited their exploration. We investigate the differences between 2D and 3D models of gap-opening planets while also comparing thermodynamical frameworks ranging from locally isothermal to fully radiative. We also compare simplified cooling recipes to fully radiative models in an effort to motivate the inclusion of radiative effects in future modeling even in a parametrized manner. We perform hydrodynamical simulations in both 2D and 3D, and then compare the angular momentum deposition by planetary spirals to assess gap opening efficiency. We repeat comparisons with different thermodynamical treatments: locally isothermal, adiabatic, local $\beta$ cooling, and fully radiative including radiative diffusion. We find that 2D models are able to capture the essential physics of gap opening with remarkable accuracy, even when including full radiation transport in both cases. Simple cooling prescriptions can capture the trends found in fully radiative models, albeit slightly overestimating gap opening efficiency near the planet. Inherently 3D effects such as vertical flows that cannot be captured in 2D can explain the differences between the two approaches, but do not impact gap opening significantly. Our findings encourage the use of models that include radiative processes in the study of planet-disk interaction, even with simplified yet physically motivated cooling prescriptions in lieu of full radiation transport. This is particularly important in the context of substructure-inducing planets in the ALMA-sensitive disk regions (>10 au).

The Nancy Grace Roman Telescope is scheduled to launch in 2026 to conduct a wide-field survey of the sky at near-infrared wavelengths. Although Roman is unable to track objects moving at non-sidereal rates, there is recent interest in the potential capability of the telescope to support planetary defense by tracking and characterizing asteroids and comets (Holler et al, 2025, arXiv:2508.14412). However, the standard pipeline image processing scheme that the mission is planning to implement for the majority of its survey data will preferentially reject flux from all moving objects during the process of cosmic ray rejection. Here we describe the impact of the default Wide Field Imager (WFI) processing on moving object detection, and possible mitigations that could be employed to recover moving object observations.

The lack of RR Lyr stars in binary systems is an atypical fact when we compared it to other classes of variables. Therefore, it has become a challenge for observers to detect an RR Lyr variable in a binary system. The RR Lyr variable KIC 2831097 was one of the most promising candidates. The phases of maximum brightness in the Kepler photometry showed a regular variation superimposed on a parabolic trend. These variations in the times of maximum brightness (Tmax ) were interpreted as a possible light-time travel effect (LTTE) in a wide binary and a fast evolutionary change in the period. We planned two spectroscopic runs with the FIES instrument mounted at the NOT to test the hypothesis of binarity. The observations were programmed at the predicted quadratures of the orbit. The GEOS collaboration complemented the spectroscopic survey by a photometric one. We also analysed Gaia time series and intensive TESS photometry. The RV curves obtained at the quadratures show the same mean RV (-203 km/s), which rules the possibility of an LTTE out. KIC 2831097 is a single high-velocity metal-poor RRc star belonging to the Galactic halo. We revisited Kepler photometry and detected a weak Blazhko effect consisting of an oscillation of only 1.1% of the period in about 50 d. We also analysed the TESS photometry of Kepler-1601, whose photometry is contaminated by KIC 2831097. In total, we collected 3624 times of maximum brightness. Linear ephemerides cannot fit the whole dataset, but only parts of them. The period shows a tendency to decrease in value, as if it were an evolutionary effect, but not at a constant rate.

Magnetic fields in pre main sequence stars regulate angular momentum evolution, drive magnetic activity, and modify stellar structure, yet their surface distributions remain poorly constrained. Traditional single component Zeeman broadening analyses typically yield mean field strengths of 2-4 kG, sometimes exceeding the photospheric equipartition limit, and assume complete magnetic coverage. These assumptions conflict with evidence that strong fields are concentrated in cool starspots. Here we present the first systematic separation of photospheric and starspot magnetic field strengths in PMS stars, using high resolution R=45000 H and K band spectra from the Raw and Reduced IGRINS Archive. By modeling temperature and magnetic field strength simultaneously for a vetted sample of 33 Class II-III young stellar objects, we find median photospheric field strengths of 1.2 kG and median spot field strengths over two times stronger at 2.56 kG, resolving the apparent super equipartition tension and removing the need for a unity magnetic filling factor. Our results show that PMS surfaces are permeated by concentrated, kG strength spot fields covering 27-83% of the visible hemisphere. This two component framework offers a physically motivated means to reconcile spectroscopic and imaging based magnetic diagnostics and enables large scale magnetic population studies across young clusters and star forming regions.

Galactic PeVatrons are astrophysical sources accelerating particles up to a few PeV (~10$^{15}$ eV). The primary method to identify both electron and proton PeVatrons is the observation of $\gamma$-ray radiation at ultra-high energies (UHE; E$>$100 TeV). In 2021, LHAASO detected 14 steady $\gamma$-ray sources with photon energies above 100 TeV and up to 1.4 PeV. Most of these sources can be plausibly associated with objects such as supernova remnants, pulsar wind nebulae, and stellar clusters. However, LHAASO J0341$+$5258 is detected as an unidentified PeVatron, emitting $\gamma$ rays at energies above hundreds of TeV. It is extended in nature and notably bright, with a flux $>$ 20% of the Crab Nebula's flux above 25 TeV. Multiwavelength observations are required to identify the PeVatron responsible for the UHE $\gamma$ rays, understand the source morphology and association, and shed light on the emission processes. Here, we will present the results from the VERITAS and HAWC observations of this PeVatron, along with a discussion on potential emission scenarios through multiwavelength modeling.

We present a new stellar dynamical measurement of the supermassive black hole (SMBH) mass in the nearby spiral galaxy NGC 4258, a critical benchmark for extragalactic mass measurements. We use archival JWST/NIRSpec IFU data (G235H/F170LP grating) to extract high-resolution two-dimensional stellar kinematics from the CO bandhead absorption features within the central $3'' \times 3''$. We extract the stellar kinematics after correcting for instrumental artifacts and separating the stellar light from the non-thermal AGN continuum. We employ Jeans Anisotropic Models (JAM) to fit the observed kinematics, exploring a grid of 12 models to systematically test the impact of different assumptions for the point-spread function, stellar mass-to-light ratio ($M/L$) profile, and orbital anisotropy. All 12 models provide broadly acceptable fits, albeit with minor differences. The ensemble median and 68% (1$\sigma$) bootstrap confidence intervals of our 12 models yield a black hole mass of $M_{\rm BH} = (4.08^{+0.19}_{-0.33}) \times 10^7$ M$_\odot$. This paper showcases the utility of using the full model ensemble to robustly account for systematic uncertainties, rather than relying on formal errors from a single preferred model, as has been common practice. Our result is just 5% larger than, and consistent with, the benchmark SMBH mass derived from water maser dynamics, validating the use of NIRSpec stellar kinematics for robust SMBH mass determination. Our analysis demonstrates JWST's capability to resolve the SMBH's sphere of influence and deliver precise dynamical masses, even in the presence of significant AGN continuum emission.

Comets have similar compositions to interstellar medium ices, suggesting at least some of their molecules maybe inherited from an earlier stage of evolution. To investigate the degree to which this might have occurred we compare the composition of individual comets to that of the well-studied protostellar region IRAS 16293-2422B. We show that the observed molecular abundance ratios in several comets correlate well with those observed in the protostellar source. However, this does not necessarily mean that the cometary abundances are identical to protostellar. We find the abundance ratios of many molecules present in comets are enhanced compared to their protostellar counterparts. For COH-molecules, the data suggest higher abundances relative to methanol of more complex species, e.g. HCOOH, CH3CHO, and HCOOCH3, are found in comets. For N-bearing molecules, the ratio of nitriles relative to CH3CN -- HC3N/CH3CN and HCN/CH3CN -- tend to be enhanced. The abundances of cometary SO and SO2 relative to H2S are enhanced, whereas OCS/H2S is reduced. Using a subset of comets with a common set of observed molecules we suggest a possible means of determining the relative degree to which they retain interstellar ices. This analysis suggests that over 84% of COH-bearing molecules can be explained by the protostellar composition. The possible fraction inherited from the protostellar region is lower for N-molecules at only 26--74%. While this is still speculative, especially since few comets have large numbers of observed molecules, it provides a possible route for determining the relative degree to which comets contain disk-processed material.

The scope of this literature review is observations of the products of first-stage evolution for binaries having components with M < 2 $M_\odot$. A taxonomy for these products comprises dwarfs ("blue stragglers"), giants ("yellow stragglers"), subdwarf B stars, and giant-like stars ("sub-subgiants" and "red stragglers"). This literature review is organized according to this taxonomy within three distinct environments: open star clusters, globular star clusters, and the Galactic field. This literature review is the Supplemental Material for Blue Stragglers and Friends: Initial Evolutionary Pathways in Close Low-Mass Binaries (Mathieu & Pols, 2025, ARAA, 63:467-512, doi: this http URL). It is intended to support and expand on Section 3 of the main text of this Annual Review of Astronomy and Astrophysics, where an integrated perspective on the common and contrasting astrophysical properties of these binary evolution products is provided. Figures used in the main text to highlight key observational results are referenced in this literature review. The closing date of this review is January 17, 2025, with some citations subsequently updated.

Quantum Gravity models suggest that singularities in gravitational collapse can be replaced by bounces, leading to the formation of Planck star remnants (PSR) that survive as stable relics once the black holes evaporate to the Planck mass. Recently, we proposed that such relics can be a viable candidate for dark matter. Here we show that LIGO's upper limit on the gravitational wave background rules out a formation pathway of Planck mass relics as dark matter from Gaussian initial conditions. This leaves non-Gaussian primordial fluctuations as the only viable channel for making Planck mass relics as dark matter.

We present a detailed analysis of a 3D MHD simulation of a subset of the magnetic flux in an active region. The simulation models the generation of nanoflares and response of the plasma to imposed photospheric motions. Our study focuses on characterizing the energy distribution and occurrence frequency of the nanoflares in the simulation that self-consistently heat the corona. This field line based analysis reveals that the nanoflare energy distribution (energy per unit cross sectional area) follows a log-normal profile, where low energy nanoflares are significantly more prevalent than those with high energy. When compared with the plasma cooling time, different energy nanoflares tend to repeat with different frequencies. Low energy nanoflares repeat at high frequencies, while high energy nanoflares repeat at low frequencies. However, the thermal evolution of plasma along individual field lines is governed predominantly by the high energy nanoflares. These findings provide critical insights into the role of small-scale magnetic reconnection events in heating the solar corona.

The HWO Target Stars and Systems 2025 (TSS25) list is a community-developed catalog of potential stellar targets for the Habitable Worlds Observatory (HWO) in its survey to directly image Earth-sized planets in the habitable zone. The TSS25 list categorizes potential HWO targets into priority tiers based on their likelihood to be surveyed and the necessity of obtaining observations of their stellar properties prior to the launch of the mission. This target list builds upon previous efforts to identify direct imaging targets and incorporates the results of multiple yield calculations assessing the science return of current design concepts for HWO. The TSS25 list identifies a sample of target stars that have a high probability to be observed by HWO (Tiers 1 and 2), independent of assumptions about the mission's final architecture. These stars should be the focus of community precursor science efforts in order to mitigate risks and maximize the science output of HWO. This target list is publicly available and is a living catalog that will be continually updated leading up to the mission.

Contamination-free assessments of the interstellar medium and star formation in quasar host galaxies, particularly based on the far-infrared, offer insights into the role of supermassive black holes in galaxy evolution. Motivated by predictions of quasar heating of dust on both nuclear and galaxy-wide scales, we perform two-component (host galaxy + point source) modeling of high-resolution (~0.1") ALMA observations of the FIR continuum in Band 5 (lambda_rest~500 um) of three highly luminous quasars (L_bol~10^47 erg/s), powered by supermassive black holes having M_BH~10^9 M_sun, at z=2. We include Band 9 (lambda_rest~154 um; 0.06" and 0.3") data at high S/N which places further constraints on the unresolved nuclear component in two cases. To break the degeneracy between quasar and stellar heating, we use CO (J=5-4), observed in Band 5, to gauge the expected contribution of star formation to the infrared luminosity. We find very good agreement between the strength and spatial distribution of the extended continuum component and its prediction based on CO (J=5-4). This is supported by the location of our three quasars along the L_(CO 5-4)-L_(IR, SFR) luminosity relation for inactive star-forming galaxies. As a consequence, there is no evidence for additional continuum emission on extended scales which could be attributed to quasar-heated dust. As expected, the nuclear (i.e., torus) contribution is present and subdominant (12% in Band 9 for one quasar with a typical star-forming host) or non-existent (<8% in Band 9 for the starbursting host). Based on the continuum and CO, the presence of substantial levels of ongoing star formation agrees with previous estimates from unresolved ALMA continuum observations which finds SFRs consistent with star-forming main-sequence galaxies. Therefore, our results do not provide evidence for a quasar-mode feedback, even for the most luminous cases at z=2.

Massive stars regulate galaxy evolution and star formation through their powerful physical and chemical feedback, but their formation remains poorly understood. Accretion powered outflows can provide important diagnostics of massive star formation. We present first results from the SOMA Atomic Outflow Survey, a far-infrared massive star formation survey using the FIFI-LS spectrometer on SOFIA. We report detection of [OIII] $^3P_2\rightarrow^3P_1$ emission at 52 $\mu$m from the massive protostar G11.94-0.62, tracing highly ionized gas. We also detect [OI] $^3P_2\rightarrow^3P_1$ and $^3P_1\rightarrow^3P_0$ at 63 and 145 $\mu$m tracing atomic gas, as well as CO $J=14\rightarrow13$ at 186 $\mu$m from highly excited molecular gas. The [OIII] and [OI] lines exhibit large line widths ($\sim400$ and $\sim40-80$ km s$^{-1}$, respectively) and their morphologies are consistent with a wide-angle bipolar outflow. Molecular tracers ($^{12}$CO, $^{13}$CO, C$^{18}$O, H$_2$CO, and CH$_3$OH) observed with ALMA also suggest a self-consistent outflow morphology. Ionized nebula/PDR modeling imply an ionized outflow mass flux of $\sim8\times10^{-5}\:M_\odot$ yr$^{-1}$ and an atomic outflow mass flux of $\sim5\times10^{-6}\:M_\odot$ yr$^{-1}$, while the molecular outflow traced by CO has an implied mass flux of $\sim3\times10^{-4}\:M_\odot$ yr$^{-1}$. The mass and momentum flux in the ionized outflow is consistent with the main component of the primary disk wind, while the molecular component is mainly swept-up, secondary outflow gas. We also observe G11.94-0.62 with the LBT in the near-infrared, potentially tracing the base of wide-angle outflow cavities. SED modeling implies $m_\star = 22.4^{+21}_{-11}\:M_\odot$, while the [OIII] emission implies $m_*\gtrsim30\:M_\odot$ and that the protostar is in the final stages of its accretion.

We explore the capabilities of time-dependent (TD) magnetohydrodynamics (MHD) solar wind simulations with the coupled WSA model of the solar corona and GAMERA model of the inner heliosphere. We compare TD with steady state (SS) simulations and with in situ data from multiple spacecraft (Earth, STEREO-A, PSP). We show that TD predictions, although better than SS predictions, substantially mispredict the solar wind at different heliospheric locations. We identified three reasons for that: (1) the uncalibrated WSA velocity formula used to generate solar wind velocities at the inner boundary of a heliospheric domain, (2) the extraction of the WSA boundary conditions for input into MHD models very high in the corona, and (3) the abrupt and partial emergence of active regions from the solar east limb. Evaluation of one year of TD predictions at Earth and STEREO-A locations shows that by tuning accordingly the WSA relationship when used with MHD models, and by extracting the WSA boundary conditions lower in the corona (at 5 Rs instead of 21.5 Rs), can lead to improved predictions. However, the abrupt emergence of active regions from the east limb of the Sun which can highly disrupt the magnetic field topology in the corona, is a difficult task to deal with since complete knowledge of the conditions on the solar far side is not currently available. Solar Orbiter Polarimetric and Helioseismic Imager (PHI) data can help mitigate this effect, however, unless we get a 4pi view of the Sun we will be unable to completely address it.

Fluctuations in the Sun's photospheric magnetic field are the primary source of the turbulence that can heat and accelerate the solar atmosphere, and thus play an important role in the production and evolution of the solar wind that permeates the heliosphere. A key parameter that characterizes this turbulence is the correlation scale of fluctuations, which determines the injection of turbulent energy into the plasma and influences the diffusive transport of solar energetic particles. This study employs magnetogram data acquired by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory to characterize an ensemble of spatial autocorrelation functions (ACFs) of magnetic fluctuations in the photosphere. It is shown that the two-point ACFs satisfy the similarity-decay hypothesis of von Kármán and Howarth, a fundamental property of turbulent systems: following a rescaling of the ACFs by energy and correlation lengths, a quasi-universal functional form is obtained demonstrating exponential decay of correlations. The probability distribution function of transverse correlation lengths (\(\lambda\)) is shown to be approximately log-normal. A mosaic of the spatial distribution of \(\lambda\) over the photosphere is presented; the ``quiet Sun'' tends to have \(\lambda\sim 1500\) km (albeit with a wide distribution), which is close to the scale of solar granulation; systematically longer lengths are associated with active regions. A positive correlation is observed between mean magnetic field magnitude and \(\lambda\), and empirical fits are derived to quantify this relationship. These results improve our understanding of the nature of turbulence in the solar photosphere and the origin of coronal and solar-wind turbulence, while providing observational constraints for models that describe the transport of turbulence from solar and stellar photospheres into their atmospheres.

We present deep Chandra X-ray observations of NGC 5005, a LINER-dominated galaxy previously reported to host a broad H$\alpha$ emission line. The diffuse soft X-ray emission ($<$3 keV) extends out to $\sim$800 pc, while harder emission ($>$3 keV) is confined to the central $\sim$400 pc. Spatially resolved spectroscopy of the nuclear ($r<150$ pc) and extended ($150<r<500$ pc) regions reveals that these are best described by models including both photoionized and thermal plasma components, consistent with excitation by a low-luminosity AGN and shock-heated gas. Narrow-band imaging and excitation maps from the Hubble Space Telescope (HST) support this interpretation, closely matching the X-ray morphology and ionization structure. The detection of a faint hard X-ray nuclear source with Chandra, combined with stringent upper limits from NuSTAR and Swift, and consistency with the X-ray luminosity predicted from the HST [O III]$\lambda$5007 emission, indicates that NGC 5005 hosts an intrinsically low-luminosity ($L_{\rm bol} \sim 10^{41}$ erg s$^{-1}$), unobscured AGN. Despite the extremely low Eddington ratio inferred from our measurements ($\lambda_{\rm Edd} \sim 5 \times 10^{-6}$), the presence of a broad H$\alpha$ line in the optical spectrum suggests the persistence of a thin accretion disk, challenging standard paradigms of accretion flow configurations at such low accretion rates.

SN 1993J is the best-studied radio supernova, with observations using very-long-baseline interferometry (VLBI) spanning from within weeks of explosion through nearly three decades of ejecta evolution. Imaging and modeling techniques have revealed an expanding shell-like ejecta structure, with a width well-constrained after ~1000 days. In this work, we present a re-analysis of the first ~1700 days of SN 1993J evolution, using a new VLBI analysis technique with somewhat intrinsically higher angular resolution and compare our results with those from previous conventional techniques. We adopt the m-ring model, with potentially somewhat higher angular resolution, but only as a phenomenological alternative to the physically-motivated spherical shell model used in past analyses and shape the profile to approximately match that of the shell. We use closure quantities only, providing calibration insensitive constraints on ejecta geometry and largely independent comparisons with previous results from the same data sets. Using this approach we find the ejecta expanding with a power-law exponent $\omega=0.80\pm0.01$ averaged for the time from 175 to 1693 days, consistent with shell-fitting analyses. For the first time, we report estimates of the ejecta width at t < 1000 days -- as early as 264 days post-explosion -- finding a mean fractional width with standard deviation of $0.24 \pm 0.04$ (of the radius) with no significant evolution. We present a fit of the azimuthal brightness modulation over time with the maximum of a horseshoe pattern rotating from east to south-southwest from 175 to 1000 d and then evolving to a more complex behavior, quantifying previous results from images only. The constraints on the angular brightness modulation and width over time and ~700 days earlier than existing analyses provide an avenue to test more advanced simulations of the explosion and interaction mechanisms.

We report the discovery and timing of two pulsars from a sample of four circularly polarized sources identified in radio continuum images taken as part of the Australian SKA Pathfinder (ASKAP) Variables and Slow Transients (VAST) survey. Observations with the Parkes (Murriyang) radio telescope confirmed both sources as normal pulsars with high dispersion measures. PSR J1646$-$4451 has a spin period of 217 ms and a dispersion measure (DM) of 928 $\rm cm^{-3} \, pc$, while PSR J1837$-$0616 exhibits a spin period of 118 ms and a DM of 793 $\rm cm^{-3} \, pc$. These pulsars show extreme pulse broadening due to scattering, with measured scattering timescales of 290 ms and 343 ms at observing frequencies of 1.8 GHz and 1.9 GHz, respectively. These measurements imply extrapolated scattering timescales at 1 GHz of 2479 ms and 2154 ms, placing them among the most heavily scattered pulsars known to date. Our findings underscore the potential of using circular polarization in radio continuum images as a tool for identifying highly scattered pulsars. Future wide-field radio continuum surveys are poised to uncover a broader population of extreme pulsars particularly those that are heavily scattered at 1.4 GHz, intrinsically faint, or residing in binaries$-$offering valuable insights into both pulsar demographics and the complex structure of the interstellar medium.

In point spread function (PSF) photometry, the selection of the fitting aperture radius plays a critical role in determining the precision of flux and background estimations. Traditional methods often rely on maximizing the signal-to-noise ratio (S/N) as a criterion for aperture selection. However, S/N-based approaches do not necessarily provide the optimal precision for joint estimation problems as they do not account for the statistical limits imposed by the Fisher information in the context of the Cramér-Rao lower bound (CRLB). This study aims to establish an alternative criterion for selecting the optimal fitting radius based on Fisher information rather than S/N. Fisher information serves as a fundamental measure of estimation precision, providing theoretical guarantees on the achievable accuracy for parameter estimation. By leveraging Fisher information, we seek to define an aperture selection strategy that minimizes the loss of precision. We conducted a series of numerical experiments that analyze the behavior of Fisher information and estimator performance as a function of the PSF aperture radius. Specifically, we revisited fundamental photometric models and explored the relationship between aperture size and information content. We compared the empirical variance of classical estimators, such as maximum likelihood and stochastic weighted least squares, against the theoretical CRLB derived from the Fisher information matrix. Our results indicate that aperture selection based on the Fisher information provides a more robust framework for achieving optimal estimation precision.

We report on the follow-up observations of circularly polarized sources identified in the MeerKAT image-based survey of the Galactic bulge. Using the Parkes radio telescope, we observed sixteen circularly polarized sources with the UWL receiver and detected nine pulsars among which six of them are new discoveries. All pulsars are fast rotators with spin periods under 100\,ms. Among the new discoveries five are millisecond pulsars (MSPs) and one has a spin period of 55\,ms. At least four new MSPs exhibit clear signs of binary motion in their discovery observations. The dispersion measures (DMs) of these pulsars fall between 18 and 330\,pc\,cm$^{-3}$, which is lower than expected for Galactic bulge members and indicates that these pulsars lie in the foreground along the line of sight rather than within the bulge itself. This is the first time such a large number of pulsars have been confirmed via an image-based survey. These discoveries underscore the exceptional efficacy of circular polarization selection in image-based pulsar surveys, and demonstrate the powerful synergy between high-sensitivity imaging and targeted time-domain follow-up using wide-band receivers and strengthen prospects for future deep pulsation searches$-$e.g., with MeerKAT or the forthcoming SKA or DSA-2000$-$to uncover the true millisecond pulsar population in the Galactic bulge.

Understanding the orbits of giant planets is critical for testing planet formation models, particularly at wide separations greater than 10 au where traditional core accretion becomes inefficient. However, constraining orbits at these separations has been challenging because of sparse orbital coverage and degeneracies in the orbital parameters. We use existing high-resolution spectroscopic measurements from CRIRES+ (R ~ 100000), astrometric data from SPHERE, NACO, and ALMA, and new high-precision GRAVITY astrometry to refine the orbit of GQ Lup B, a ~30 M_J companion at ~100 au, in a system that also hosts a circumstellar disk and a wide companion, GQ Lup C. Including radial velocity data significantly improves orbital constraints by breaking the degeneracy between inclination and eccentricity that affects astrometry-only fits for long-period companions. This work is among the first to combine high-precision astrometry with the companion's relative radial velocity to achieve improved orbital constraints. The eccentricity is refined from e = 0.47 (+0.14, -0.16) with GRAVITY alone to e = 0.35 (+0.10, -0.09) when RVs and GRAVITY data are combined. The orbit is misaligned by 63 (+6, -14) deg relative to the circumstellar disk and 52 (+19, -24) deg relative to the host star spin axis, and is more consistent (34 (+6, -13) deg) with the inclination of the wide tertiary companion GQ Lup C disk. These results support a formation scenario for GQ Lup B consistent with cloud fragmentation and highlight the power of combining companion RV constraints with interferometric astrometry to probe the dynamics and formation of wide-orbit substellar companions.

We present a physically interpretable framework to quantify dynamical disturbances in galaxy clusters using projected two-dimensional phase-space information. Based on the TNG-Cluster simulation, we construct a disturbance score that captures merger-driven asymmetries through features such as velocity dispersion and Gaussian Mixture Model (GMM) peak fitting, which captures asymmetries indicative of dynamical disturbance. All features are derived from observable quantities and are intended to be measurable in future surveys. To enable observational application, we adopt a simplified estimator using aperture mass map statistics as a mass ratio proxy in TNG300-1, and validate its performance with weak lensing data from The Local Volume Complete Cluster Survey (LoVoCCS). While phase-space diagnostics reveal merger-driven asymmetries, they are not sensitive to whether the secondary progenitor is infalling or receding, and thus cannot distinguish future mergers from past mergers. To address this, we incorporate the star formation rate (SFR) from TNG-Cluster and propose the blue galaxy fraction as a promising observational tracer of merger timing. Finally, we construct mock Chandra X-ray images of TNG-Cluster halos at redshift $z=0.2$, and find that the offset between the X-ray peak and the position of the most massive black hole (used as a proxy for the Brightest Cluster Galaxy, BCG) correlates with our disturbance score, serving as a consistency check. We also perform case studies using LoVoCCS observational data, correlating the blue galaxy fraction with disturbance scores derived from the eROSITA morphology catalog.

We present a comparative analysis of estimators and Bayesian methods for determining the number count dipole from cosmological surveys. The increase in discordance between the number count dipole and the CMB's kinematic dipole has presented a challenge to the assumption of an isotropic and homogeneous universe. The level of discordance has depended on the choice of method to determine the dipole; hence, there is a need to compare them to determine the better approach. We select the healpy fit_dipole algorithm as our estimator and show that it gives unbiased results regardless of the noise levels and sky coverage in the data. However, for low sky coverage, the estimator's results have a large variance, which indicates that the estimator is not reliable in that regime. We then compare the estimator's outputs with the Bayesian results. If the sky coverage is sufficient, the Bayesian posterior probabilities agree with both the estimator's outcomes and the true parameter values. But if the sky coverage is low, Bayesian analysis is often inconclusive, which safeguards against incorrect conclusions. Both methods provide the ability to analyse multiple samples: on one hand, we need to select a different estimator, while in Bayesian inference, we need to extend our likelihood function to incorporate additional parameters. Our study emphasises the need to perform a principled statistical analysis of sky surveys for dipole determination.

Collisionless dissipation of turbulence is important for heating plasmas in astrophysical, space physics, and laboratory environments, controlling energy, momentum and particle transport. We analyze Parker Solar Probe observations to understand the collisionless heating of the sub-Alfvénic solar wind, which is connected to the solar corona. Our results show that linear resonant heating through parallel-propagating cyclotron waves cannot account for turbulent dissipation in sub-Alfvénic region, which observations suggest may dissipate turbulence at distances further from the Sun. Instead, we find that stochastic heating can account for the observed ion energization; however, because the dominant contributions arise from infrequent, large-amplitude events, turbulent intermittency must be explicitly incorporated. These observations directly connect stochastic heating via breaking of the proton magnetic moment with the intermittent and inhomogeneous heating of turbulence reported in many previous studies. Our identification of stochastic heating as a dynamic mechanism responsible for intermittent heating of the solar wind has significant implications for turbulent dissipation in the lower corona, other astrophysical environments, and laboratory plasma.

Type II supernovae (SNe II) are the most frequently observed outcome of core-collapse explosions and provide a valuable window into the physical mechanisms governing the deaths of massive stars. However, estimates of explosion properties based on optical light curve modeling often show tension with the predictions of modern neutrino-driven explosion models. In particular, when based on light curves from the explosions of red supergiant (RSG) tied to specific stellar wind models, many SNe II are found to originate from low-mass progenitors yet exhibit unusually high explosion energies ($E_{\rm K}$), far exceeding theoretical predictions. In this study, we incorporate late-phase (nebular) spectroscopy to estimate the helium core mass of the progenitor ($M_{\rm He\,core}$), which serves as an additional constraint to break degeneracies in light curve modeling. This approach is applied to a sample of 32 well-observed SNe II, using a light curve model grid constructed from RSGs with arbitrarily stripped hydrogen-rich envelopes, rather than assuming a fixed wind model. Examining the resulting correlations among the physical parameters, we find that the tension between the observed $M_{\rm He\,core}$-$E_{\rm K}$ and $E_{\rm K}$-$M_{\rm Ni}$ relations and those predicted by neutrino-driven explosion models has significantly lessened by incorporating nebular spectroscopy in light curve modeling. This study highlights the crucial role of nebular spectroscopy in interpreting SNe II observations and provides support to the neutrino-driven explosion mechanism as the dominant engine powering these events.

Large Array of imaging atmospheric Cherenkov Telescope (LACT) is an array of 32 Cherenkov telescopes with 6-meter diameter mirrors to be constructed at the LHAASO site, aiming to enhance our understanding of ultra-high energy gamma ray astronomy. This work presents a detailed performance assessment of the LACT array, focusing on the IRFs for both an 8-telescope subarray configuration optimized for large zenith angle observations (60°) and the full 32-telescope array, with a particular emphasis on a 20° zenith angle configuration for lower energy threshold observations. We have generated IRFs using extensive Monte Carlo simulations of gamma-ray showers and the detector response. The IRFs include the effective area, angular resolution, and energy resolution as a function of energy and offset angle. Crucially, these IRFs are produced in the standard Data format for Gamma ray astronomy (GADF), ensuring interoperability with existing analysis tools like Gammapy and ctools and enabling seamless integration into scientific workflows. In this work, we also have used these GADF-format IRFs to simulate observations towards the Galactic Center Region.

We summarize the motivation for (as well as the presentations from) the April, 2024 workshop held in India and focused on radiowave techniques for cosmic ray and neutrino detection.

Galaxy mergers funnel gas toward the nuclei, igniting starbursts and active galactic nuclei (AGNs). The AGN feedback can reshape the host galaxy and regulate both star formation and super-massive black-hole (SMBH) accretion. Using VLT/MUSE integral-field spectroscopy, we conduct a spatially resolved study of the triple-AGN candidate SDSS J0849+1114. Extended ionized gas structures ($>10$ kpc from nucleus A) primarily associated with tidal tails are detected. Meanwhile, two distinct ionized gas outflows are revealed. One extends over $>5$ kpc around nuclei A with a kinetic power of $\dot{E}_{\rm out,A} = 3.0\times10^{42}\rm\, erg\, s^{-1}$, which might be driven by the radio jet. The other outflow extends $\sim 5.9$ kpc around nucleus C, with a kinetic power of $\dot{E}_{\rm out,C} = 2.0\times10^{40}\rm\, erg\, s^{-1}$. High [O III]/H$\alpha$ and [N II]/H$\alpha$ ratios in the tidal gas require that nucleus A radiated at a high accretion rate with $L_{\rm A,bol} \sim 0.1$--$0.5\,L_{\rm Edd,A}$ at least $\sim3$--$\times10^{4}\rm\,yr$ ago, $20$--$100$ times brighter than today. Combined with multi-wavelength constraints, we find evidence for episodic AGN feedback that expelled circumnuclear gas and rapidly quenched accretion. This triple AGN candidate demonstrates how AGN feedback can self-regulate black hole growth and impact hosts during mergers.

The search for extraterrestrial intelligence (SETI) is largely limited by the vastness of the signaling parameter space. The concurrent signaling scheme offers a framework in which civilizations can coordinate their transmission and reception by referring to a common astrophysical event. Building on this idea, I propose a hybrid strategy that combines the Galactic Center as a spatial reference with an extragalactic burst as a temporal marker. If such a scheme is indeed employed, the sky area to be surveyed in SETI could be reduced by more than two orders of magnitude, based solely on existing astronomical data. I examine records of three types of extragalactic bursts (supernovae, neutron star mergers, and gamma-ray bursts [GRBs]) to identify suitable temporal markers. Among them, GRB 221009A is particularly notable due to its high fluence and favorable sky location.

High-resolution far-infrared (FIR) observation of submillimeter galaxies (SMGs) is an effective approach to study the formation of sub-structures in the early epoch of massive galaxies. We present the 870$\mu$m continuum images resolved down to sub-kpc scales for 12 SMGs taken by Atacama Large Millimeter/Submillimeter Array (ALMA) as an initial sample of the FOSSILS Survey. We discovered a wide variety of morphological properties, including a two-arm spiral galaxy at $z=2.5$ possibly induced by a tidal interaction with a minor companion. Nonetheless, about half of the sample exhibit a compact and circular morphology, which is reminiscent of optical morphology of compact quiescent galaxies. Future studies with larger sample and combination of the rest-frame optical images taken by James Webb Space Telescope will shed light on the various evolutionary track of SMGs.

Generally, merger likelihood increases in denser environments; however, the large relative velocities at the centres of dense clusters are expected to reduce the likelihood of mergers for satellite galaxies. Tidal features probe the recent merger histories of galaxies. The Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) will produce an unprecedented sample of tidal features around millions of galaxies. We use LSST-like mock observations of galaxies at $z\sim0$ from the EAGLE, IllustrisTNG and Magneticum Pathfinder cosmological-hydrodynamical simulations to predict the occurrence rates of tidal features around satellite galaxies across group and cluster environments in the velocity-radius projected phase-space diagram to investigate the impact of these environments on tidal feature occurrence. We find that ancient infallers in the projected phase-space exhibit a decreasing tidal feature fraction with increasing halo mass, whereas recent infallers in the projected phase-space show unchanging tidal feature fractions with halo mass. Our results show, for the first time in cosmological simulations, a suppression of tidal feature fractions in the central regions of galaxy clusters, indicating a reduced merger rate due to higher cluster-centric velocities and lower galaxy total masses in the cluster centres. Using a toy model, we show that the presence of more tidal features in the recent infaller zone and cluster outskirts suggests that tidal features occur in interactions within infalling groups and dissipate by the time they are ancient infallers, indicating a $\lesssim3\pm2$ Gyr survival time of tidal features within clusters.

The Askaryan Radio Array (ARA), located near the South Pole, is among the first experiments there designed to detect ultra-high energy neutrinos through the Askaryan effect. When such neutrinos interact in dense media like ice, they initiate particle cascades that generate coherent radio pulses. Operating in the 150-850 MHz band, ARA is deployed 80-200 meters deep in Antarctic ice, where the radio background is exceptionally low. Despite this, experiments such as ARA must still account for continuous wave (CW) signals, which can originate from anthropogenic sources, instrumental noise, and other environmental factors. These CW signals can obscure faint neutrino-induced pulses, complicating data analysis and event identification. Over the years, ARA has developed and refined techniques for CW filtering and identification, including spectral analysis, notch filtering, and phase-variance methods. These approaches exploit CW characteristics such as their narrowband nature and persistence to separate contamination from genuine impulsive events. We review the main CW identification and filtering techniques developed within the ARA collaboration and present recent improvements in adaptive, multi-stage filtering pipelines. These advances have led to faster processing, simpler operation, and more accurate CW suppression, improving data analysis quality. Their efficacy is demonstrated across all ARA stations, underscoring their role in reducing event misclassification and enhancing performance. By refining these techniques, this work not only improves the sensitivity of ARA but also highlights the importance of robust CW filtering for current and future neutrino radio detection experiments.

The emissivity profile assumed in X-ray reflection spectroscopy significantly impacts black hole spin measurements. Using simulated NuSTAR spectra generated for lamppost and disk-like coronae with the relxill model suite, we evaluate systematic biases introduced when fitting with power-law or broken power-law emissivity profiles. We find that a simple power-law can accurately recover spins for low-height lamppost coronae with long exposures and low inclination angle, while broken power-laws introduce degeneracies when the simple power-law already performs adequately. However, for extended or high-height coronae, especially at high inclinations, both models produce large systematic biases unresolved by longer exposure times. Our results demonstrate that power-law approximations are reliable for compact coronae, highlighting the need for geometry-specific models in complex cases.

In this study, we analyzed millimeter-wave data toward the quasar PKS1830-211 observed with the Atacama Large Millimeter/submillimeter Array to obtain absorption spectra of HCN $J$=2-1, $J$=3-2, $J$=4-3, and $J$=5-4 lines at the cosmological redshift of $z=0.89$. We confirmed multiple absorption components in each spectrum, and the two lower-$J$ lines are highly saturated at velocity centers of the two most prominent components. The effect of uncertainty in the continuum covering factor was carefully assessed using a Monte Carlo approach. We also accounted for systematic uncertainties in the HCN $J$=4-3 and $J$=5-4 absorption due to time variability during an intense flaring event of the quasar. Assuming local thermodynamic equilibrium and neglecting molecular collisions, we derived the excitation temperature profiles and their uncertainties in the optically thin regime. We determined the cosmic microwave background radiation temperature at $z = 0.89$ to be ${5.13\pm0.06\,\mathrm{K}}$ by taking a weighted average of calculated excitation temperatures; this is highly consistent with that expected from the standard model of the universe.

We propose that the high eccentricity of the stellar orbit in Gaia BH3 system could be excited through a secular resonance effect if the inner dark object is, in effect, a tight and eccentric black hole binary (BHB). During the orbital decay of the inner BHB, the apsidal precession rate of the inner binary matches that of the outer stellar orbit, and this resonance advection can drive the outer eccentricity into some extreme values. For a Gaia BH3-like system, we show that a near equal-mass ($q=0.8$) BHB with an initial semi-major axis of 1--3 au and an initial eccentricity $\gtrsim 0.95$ is able to excite the outer orbit to the observed value, leaving a current BHB with semi-major axis 0.25--0.5 au and eccentricity $\sim 0.8$. The eccentric inner BHB imprints two observable signatures on the outer star: (1) short-term RV modulations with an amplitude $\lesssim 100$ m/s and (2) long-term apsidal precession with a rate $\lesssim 0.1^{\circ}$/yr. Although neither of these is detected in the currently available astrometry and RV data, we show that these signals are detectable with the full Gaia astrometry data and dedicated high-precision and/or long-term RV observations. Our work provides a new perspective on the dynamical formation of Gaia BH3, and the methodology is readily applicable to similar systems such as HD 130298, Gaia BH1, and Gaia BH2.

We report the discovery of a kpc scale molecular contrail in the spiral galaxy NGC 3627, a narrow structure spanning 8 kpc in length with a width of 200 pc and an extreme aspect ratio of 40, observed in both mid-infrared dust emission (PHANGS-JWST) and CO(2-1) gas (PHANGS-ALMA). This contrail size significantly exceeds the size of any known analogs in the Milky Way and exhibits supersonic turbulence (10 km/s). Its morphology and dynamics are consistent with gravitational focusing by a flyby compact object of mass 1e6 M_sun, likely a massive black hole or a dwarf galaxy nucleus, traversing the disk at >300 km/s. The crossing time of such a contrail, estimated from its width and velocity dispersion, is only $\sim 20$ Myr, implying a recent interaction. This contrail can be caused by a dwarf galaxy, or massive black hole nucleus. This discovery establishes galactic-scale contrails as probes of massive dark objects interacting with medium in and around galactic disks.

We present a model-independent determination of the Hubble constant ($H_0$) using the latest observational data from multiple cosmological probes. By combining baryon acoustic oscillation (BAO) measurements from the second data release of the Dark Energy Spectroscopic Instrument (DESI DR2), cosmic chronometer $H(z)$ data, and the Pantheon Plus Type Ia supernova (SN Ia) sample, we reconstruct the cosmic expansion history through Gaussian process regression without assuming a specific cosmological model or relying on sound horizon calibration. Our analysis incorporates the complete covariance structure of the measurements and yields $H_0$ constraints at five distinct redshifts: $65.72 \pm 1.99$ (z=0.51), $67.78 \pm 1.75$ (z=0.706), $70.74 \pm 1.39$ (z=0.934), $71.04 \pm 1.93$ (z=1.321), and $68.37 \pm 3.95~\mathrm{km~s^{-1}~Mpc^{-1}}$ (z=1.484). The optimal combination of these measurements gives $\hat{H}_0 = 69.0 \pm 1.0~\mathrm{km~s^{-1}~Mpc^{-1}}$ with 1.4\% precision, which occupies an intermediate position between the Planck CMB result and the SH0ES local measurement and is consistent with the TRGB result. Rather than providing a single integrated $H_0$ value, our approach delivers independent constraints at multiple redshifts, thereby enabling a detailed investigation of potential redshift-dependent systematic effects that could contribute to the Hubble tension. We identify significant correlations between adjacent redshift bins ($\rho = -0.033$ to $0.26$), primarily arising from the BAO covariance and reconstruction effects. These results demonstrate a clear redshift evolution in Hubble constant measurements and suggest that the Hubble tension may involve more complex redshift-dependent effects than a simple dichotomy between early and late universe probes.

We discover an extended distribution of main-sequence (MS) stars along the minor axis of the Ursa Minor (UMi) dwarf spheroidal galaxy (dSph). This study is enabled by deep, wide Subaru/Hyper Suprime-Cam data, reaching photometric uncertainties below 0.1 mag at $g,i \sim 26$ mag. Color-magnitude diagrams along the major and minor axes reveal a clear excess of MS stars beyond the nominal tidal radius along the minor axis. To characterize this structure, we derive radial number density profiles in seven azimuthal directions and fit them with an exponential+power-law function to assess the symmetry of the extended component. The power-law slopes tend to be shallower toward the minor axis, though the symmetry remains inconclusive within 1$\sigma$ uncertainties. This may indicate that the extended component is preferentially distributed along the minor axis, and could be different from the previously suggested tidal features along the major axis. Comparing with simulations, we find that the fraction of stars beyond five effective radii is consistent with expectations from an intermediate mass ratio merger scenario with a stellar mass ratio around 6:1. While these findings provide new insights into the structural complexity and dynamical history of the UMi dSph, alternative mechanisms such as stellar or supernova feedback have also been proposed for extended stellar halos in dwarfs and cannot be ruled out.

Several short-lived radionuclides (SLRs) are know to have existed in the early Solar System (ESS). These species, which typically decay with half-lives of the order of a few million years, can be used to probe the timescale of events preceding the birth of the Sun. We investigate the ESS origin of $^{53}$Mn, produced by core-collapse (CCSNe) and Type Ia supernovae (SNe Ia), and $^{60}$Fe, produced exclusively by CCSNe. We model the evolution of the radioactive-to-stable abundance ratios of these SLRs with a galactic chemical evolution (GCE) framework accounting for different supernova yields, SN Ia delay times, and other galactic features $(K)$. A further set of models are calculated assuming that SN Ia did not contribute any $^{53}$Mn to the ESS. The predicted ratios are compared to meteoritic ratios to derive a distribution of solar isolation times that includes uncertainties due to stochastic chemical enrichment and precision of the ESS values. The isolation times are then compared to those of $^{107}$Pd and $^{182}$Hf calculated in previous work. A self-consistent solution can be found within the current uncertainties, especially when using the GCE setups with $K = 1.6$ and 2.3, although the maximum likelihood for the \iso{60}Fe distribution is typically $\sim 4-5$ Myr shorter than for \iso{53}Mn. The predicted \iso{60}Fe/\iso{53}Mn ratio, instead, is completely inconsistent with the ESS value; this could be resolved using a larger fraction of faint CCSNe than usually considered in GCE models.

Isoprene and its oligomers, terpenes, are expected to be present, along with other complex organic molecules, in the diverse environments of the ISM and in our solar system. Due to insufficient spectral information of these molecules at low temperature, the detection and understanding of the importance of these molecules has been rather incomplete. For this purpose, we have carried out the vacuum ultraviolet (VUV) photoabsorption measurements on pure molecular ices of isoprene and a few simple terpenes: limonene, $\alpha$-pinene and $\beta$-pinene by forming icy mantles on cold dust analogs. From these experiments, we report the first low-temperature (10 K) VUV spectra of isoprene and its oligomers, limonene, $\alpha$-pinene, and $\beta$-pinene. VUV photoabsorption spectra of all the molecules reported here reveal similarities in the ice and gas phase, as expected, except for isoprene, where a prominent red shift is observed in the ice phase absorption. This unique property of isoprene, along with distinctive absorption at longer wavelengths, supports its candidature for detection on icy bodies.

Cosmic rays reaching the atmosphere of an astrophysical object produce showers of secondary particles that may then scape into space. Here we obtain the flux of gammas and neutrinos of energy $E>10$ GeV emited by the Sun, Jupiter and Earth. We show that, while the solar magnetic field induces an albedo flux of gammas from all the points in the Sun's surface, the dipolar magnetic field in the planets implies gammas only from the very peripheral region. Neutrinos, in contrast, can cross these objects and emerge from any point in their surface. The emission from these astrophysical objects is above the diffuse flux from cosmic ray interactions with the interstellar medium and has a distinct spectrum and gamma to neutrino ratio.

Currently, the number of galaxy clusters identified using galaxy data has far exceeded the number derived from intracluster medium data. In this study, we used positional information from large optical cluster catalogues to search for previously unrecognized X-ray galaxy clusters in archival XMM-Newton data. We successfully identified 1490 galaxy clusters in X-ray images for the first time. By incorporating 1913 previously known X-ray clusters, we constructed a sample of 3403 galaxy clusters observed by XMM-Newton. Our cluster mass estimates show broad consistency with previous measurements. Comparative analyses between the known and newly identified subsamples revealed that new X-ray clusters exhibit systematically higher redshifts, lower masses, and smaller X-ray-to-optical mass ratios, but show no systematic differences in dynamical properties. The newly identified X-ray clusters are a valuable addition to previous X-ray samples and are important for future statistical studies.

Microquasars are increasingly recognized as efficient particle accelerators, potentially contributing to the cosmic-ray flux up to the "knee". Among them, SS 433 stands out as a unique system with precessing relativistic jets embedded within the W50 supernova remnant. Recent detections of very- and ultra-high-energy gamma rays from SS 433 have solidified its role as a key laboratory for studying particle acceleration in jet-powered astrophysical sources. We present results from over 100 hours of observations of SS 433 with VERITAS, spanning more than a decade. These high-resolution measurements allow for a detailed morphological study of the eastern and western jet lobes with an angular resolution of <0.1°. By analyzing the spatial and spectral characteristics of the gamma-ray emission, we investigate the particle acceleration mechanisms within the jets and at the jet-medium interaction in W50.

The accretion luminosity (Lacc) in young, low-mass stars is crucial for understanding stellar formation, but direct measurements are often hindered by limited spectral coverage and challenges in UV-excess modeling. Empirical relations linking Lacc to various accretion tracers are widely used to overcome these limitations. This work revisits these empirical relations using the PENELLOPE dataset, evaluating their applicability across different star-forming regions and to accreting young objects other than Classical T Tauri Stars (CTTSs). We analyzed the PENELLOPE VLT/X-Shooter dataset of 64 CTTSs, measuring fluxes of several accretion tracers and adopting the stellar and accretion parameters derived from PENELLOPE works. We supplemented our analysis with the ODYSSEUS HST data set, which covers a wider spectral range in NUV bands. We compared the Lacc values obtained in the PENELLOPE and ODYSSEUS surveys finding statistically consistent results. Our analysis confirms that existing empirical relations, previously derived for the Lupus sample, provide reliable Lacc estimates for CTTSs in several other star-forming regions. We revisit empirical relations for accretion tracers in our dataset, based on HST-fit, with coefficients which are consistent within 1sigma with XS-fit results for most lines. We also propose a method to estimate extinction using these relations and investigate the empirical relations for Brackett lines (Br8 to Br21). The Lacc vs Lline empirical relations can be successfully used for statistical studies of accretion on young forming objects in different star-forming regions. These relations also offer a promising approach to independently estimate extinction in CTTSs. We confirm that near-infrared lines (PaB and BrG) reliably trace Lacc in high accretors, making them valuable tools for probing accretion properties of high accreting young stars not accessible in the UVB.

X-ray pulsars (XRPs) consist of a magnetized neutron star (NS) and an optical donor star. The NS accretes matter from the donor star producing pulsed X-ray emission. In most cases the donor stars are Be stars, and accretion is episodic, that is, the NSs are generally X-ray dim, but occasionally experience outbursts. Here, we carry out a statistical study with the X-ray monitoring data, and obtain strong correlations between the spin periods of the NSs and the outburst parameters for the first time. We show that XRPs containing faster rotating NSs tend to display more violent eruptions. In addition, pulsating ultraluminous X-ray sources in nearby galaxies follow the similar relationship. We demonstrate that most of these systems are close to the spin equilibrium, and that brighter pulsars have acquired more angular momentum by accreting matter from their companion stars, resulting in faster rotating NSs.

Both the Rubin Observatory and the first telescopes of the CTAO will be collecting data by 2026, marking a new era in optical and gamma-ray astronomy. Compared to predecessors, their enhanced sensitivity will extend extragalactic observations to a redshift of at least 2.5. This advancement offers insights into non-thermal astrophysical sources, particularly blazars. The 3-night cadence monitoring with Rubin, in one of its six filters, will produce blazar light curves that, when combined with targeted in-depth observations from the CTAO, could help distinguish acceleration and radiative models. Existing data from the ZTF and Fermi-LAT, though less sensitive, offer insights into what Rubin and the CTAO may achieve. However, the real-time processing of the immense data stream coming from Rubin/LSST presents a major challenge. Addressing this challenge is the work of brokers such as Fink, which we develop for multi-messenger astrophysics. Fink processes data in real-time before sending relevant information to other observatories like the CTAO. In this contribution, we present how we characterize the optical variability of blazars that emit in the gamma-ray range using the ZTF, with timescales spanning from the intra-night to multi-years. We identify properties in the resulting parameter space that could not only enable the identification of blazar-like sources, but also the characterization of the continuum of states. We describe our fast identification of transitions from one state to another, enabling the trigger of observations in the gamma-ray band and follow-up spectroscopic observations. Finally, we review the communication channel we set from the ZTF to the CTAO via Fink for blazars and discuss its outlook in light of the Rubin Observatory. This method is also applicable to other astrophysical sources and helps lay the groundwork for a fruitful era for time-domain astronomy.

The inverse cascade in MHD turbulence plays a crucial role in various astrophysical processes such as galaxy cluster formation, solar and stellar dynamo mechanisms, and the evolution of primordial magnetic fields in the early universe. A standard numerical approach involves injecting magnetic helicity at intermediate length scales to generate a secondary, time-dependent spectral peak that gradually propagates toward larger scales. Previous simulations have already suggested a resistive dependence of inverse transfer rates and demonstrated the significant influence of magnetic helicity flux density $\epsilon_\mathrm{H}$ on this process. On dimensional grounds, we have $E_\mathrm{M}(k,t)=C_\mathrm{H} \epsilon_\mathrm{H}^{2/3} k^{-1}$ where $C_\mathrm{H}$ represents a potentially universal dimensionless coefficient analogous to the Kolmogorov constant. We present a summary of the 25 distinct simulations conducted with the \textsc{Pencil Code}, systematically varying the forcing wavenumber $k_\mathrm{f}$, magnetic Prandtl number $Pm$, grid resolution $N^3$, and Lundquist number $Lu$. We obtained $C_\mathrm{H}$ and corresponding error bars by calculating the compensated spectrum and investigated its dependence with $Lu$ and $k_\mathrm{f}$. For the $C_\mathrm{H}$ - $Lu$ relationship, we observe strong correlations with power-law exponents of 1 and 2/3. In contrast, we find no significant correlation between $C_\mathrm{H}$ and $k_\mathrm{f}$.

Relativistic jets generated in gamma-ray bursts (GRBs) produce luminous transient events, yet the fundamentals of jet composition and radiation mechanisms remain unclear. One means of identifying a magnetically-dominated outflow would be detection of prompt, coherent radio emission at low frequencies, and we are able to search for this using the LOw Frequency ARray (LOFAR) coupled with modelling of high energy pulses detected by the Neil Gehrels Swift Observatory (Swift). We present the rapid response mode follow-up LOFAR observations of four long GRBs, each beginning within a few hundred seconds of the initial Swift-BAT trigger. We interpreted our findings under the framework of a magnetic wind model, predicting coherent radio emission analogous to prompt emission pulses. Using 60 second and 180 second time sliced imaging at 120-168 MHz, we obtain upper limits on radio pulse emission, finding no significant signals. In the case of GRB 200925B, we observed a small increase of radio flux seen at $\sim$60-360 s post burst. In this model, this could represent the radio emission related to the Swift-BAT pulses, for a redshift of $z=1.8$, however, with a low signal-to-noise ratio of $\sim 2$, it is not deemed significant enough to confirm coincident prompt radio and gamma-ray emission. Instead, we can constrain the $\epsilon_{B}$ parameter, deriving upper limits of $\epsilon_{B} < 4.2 \times 10^{-4}$ for GRB 200925B. In GRB 240414A, with a reported redshift of $z=1.833$, we constrain $\epsilon_{B} < 2.8 \times 10^{-4}$. We discuss these results in the context of our whole LOFAR rapid response sample of six long gamma-ray bursts, finding our $\epsilon_{B}$ values are generally consistent with previous GRB studies.

Prestellar cores represent the initial conditions of star formation, but heavy molecules such as CO are strongly depleted in their cold, dense interiors, limiting the ability to probe core centers. Deuterated molecular ions therefore emerge as key tracers because deuterium fractionation is enhanced at low temperatures. We present the first direct observation of ortho-H2D+ depletion in the prestellar core G205.46-14.56M3 using ALMA 820um continuum and ortho-H2D+(110-111) data at ~300-au resolution. We confirm the previously reported two substructures, B1 and B2, and identify a central ortho-H2D+ depletion zone toward B1 with ~6$\sigma$ contrast and an inferred diameter $\lesssim$600au, together with a peak $x$(N2D+)/$x$(N2H+)=$1.03^{+0.07}_{-0.56}$. The observationally inferred profiles of $x$(ortho-H2D+) and $x$(N2D+)/$x$(N2H+) are reproduced by a deuteration-focused chemo-dynamical model; however, the central ortho-H2D+ depletion is only marginally matched within the $2\sigma$ upper limit, likely suggesting additional deuteration in the depletion zone. From these models we infer a core age of ~0.42Ma, comparable to the free-fall time, suggesting that the substructures formed via rapid, turbulence-dominated fragmentation rather than slow, quasi-static contraction. Our observations also reveal that ortho-H2D+ velocity dispersions are largely subsonic in the core and nearly thermal between B1 and B2, consistent with turbulence dissipating within a few free-fall times. These results highlight the critical role of deuterated ions for both chemical evolution and dynamics in dense cores.

The low-mass X-ray binary (LMXB) GX 1+4 stands out with its unique properties. Despite being an old system, it hosts a strongly magnetized neutron star (NS), a trait usually linked to younger systems. Its exceptionally long orbital period (1160 days) and low eccentricity (0.101) imply that the NS formed with minimal mass loss and a weak natal kick. These features collectively point towards the NS having formed through the accretion induced collapse (AIC) of a white dwarf (WD). However, GX 1+4's unusually high peculiar velocity (~ 189.36 km/s) defies standard AIC explanations. To address this discrepancy, we propose a two-stage kick scenario within the AIC framework: an initial natal kick followed by a delayed electromagnetic "rocket effect" kick. Our Monte Carlo simulations indicate that while the natal kick (< 100 km/s) can generate a wide range of orbital eccentricities, the subsequent rocket kick (~ 240-480 km/s) explains both the high systemic velocity and low eccentricity. This two-stage kick mechanism naturally reproduces the observed characteristics of GX 1+4, provided that the NS's initially buried magnetic field re-emerges after the acceleration process ends. Our study represents the first attempt to quantitatively constrain the kick velocities in GX 1+4 and underscores the importance of possible rocket kicks in forming such peculiar LMXB systems.

We have evaluated the rate at which the asteroid belt is losing material, and how it splits between macroscopic bodies and meteoritic dust. The mass loss process is due to the injection of asteroid fragments into unstable dynamical regions, associated to mean-motion resonances with Jupiter, Saturn and Mars or secular resonances, from where they are scattered either to the region of the terrestrial planets or to the vicinity of Jupiter's orbit. Asteroid fragments that do not escape from the belt are ground down by mutual collisions to meteoritic dust. Under the assumption that 25\% of the zodiacal dust mass is of asteroidal origin, we find that the asteroid belt is currently losing a fraction of about $\mu_o \simeq 8.8 \times 10^{-5}$ Ma$^{-1}$ of its collisionally-active mass (without the primordial objects Ceres, Vesta and Pallas), about 20\% as macroscopic bodies, and 80\% as dust particles that feed the zodiacal dust cloud. Extrapolation of the current mass loss rate to the past suggests only a moderate increase of the asteroid belt mass and the mass loss rate around 3.0 - 3.5 Ga ago (by about 50\% and a factor of two respectively). Yet, should the computed $\mu_o$ be somewhat underestimated owing to the different uncertainties associated to its computation, the extrapolation to the past would lead to quite different results. For instance, a moderate increase in the computed $\mu_o$, say by a factor of three, would lead to an exponential increase of the asteroid mass and mass loss rate about 3.5 Ga ago. A greater asteroid mass loss rate in the past should be correlated with a more intense impact rate of the Earth, Moon and the other terrestrial planets, which is indeed what suggests the geologic record (Hartmann 2007).

Accurate pulsar astrometric estimates play an essential role in almost all high-precision pulsar timing experiments. Traditional pulsar timing techniques refine these estimates by including them as free parameters when fitting a model to observed pulse time-of-arrival measurements. However, reliable sub-milliarcsecond astrometric estimations require years of observations and, even then, power from red noise can be inadvertently absorbed into astrometric parameter fits, biasing the resulting estimations and reducing our sensitivity to red noise processes, including gravitational waves (GWs). In this work, we seek to mitigate these shortcomings by using pulsar astrometric estimates derived from Very Long Baseline Interferometry (VLBI) as priors for the timing fit. First, we calibrated a frame tie to account for the offsets between the reference frames used in VLBI and timing. Then, we used the VLBI-informed priors and timing-based likelihoods of several astrometric solutions consistent with both techniques to obtain a maximum-posterior astrometric solution. We found offsets between our results and the timing-based astrometric solutions, which, if real, would lead to absorption of spectral power at frequencies of interest for single-source GW searches. However, we do not find significant power absorption due to astrometric fitting at the low-frequency domain of the GW background.

This paper is the second in a series presenting \textsc{RadioSED}, a Bayesian inference framework for constructing, modelling and classifying radio spectral energy distributions from publicly-available surveys. We focus here on the application of our framework to SDSS Stripe 82. Not only do we recover all eleven previously-published peaked spectrum sources from the literature within this region, but we increase the number of known peaked spectrum sources here by more than an order of magnitude. We investigate the variability properties of our peaked spectrum sample, and find that overall they exhibit a low degree of variability, consistent with previous samples of peaked spectrum active galactic nuclei. The multiwavelength properties of these sources reveal that we have selected a population comprising largely distant ($z \geq 1$), powerful active galaxies. We find that the most compact jets are located preferentially in quasar-type hosts, with galaxy-type hosts home to slightly more extended radio structures. We discuss these findings in the context of current and forthcoming large area radio surveys.

Early results from JWST uncover a peculiar class of objects referred to as ``little red dots'' (LRDs). The extremely compact morphology of LRDs is often invoked to point towards an AGN-dominated picture in the context of their conflicting multiwavelength properties. In this work, we assess the capability of pysersic and GALFIT -- commonly used tools in LRD morphological studies -- to recover input parameters for a simulated suite of LRD-like objects in the F444W band. We find that: 1) these tools have difficulty recovering input parameters for simulated images with SNR $\lesssim 25$; 2) estimated PSF fraction could be a more robust physically-motivated description of LRD compactness; and 3) almost all permutations of modeled LRDs with SNR $\lesssim 50$ cannot be differentiated from a point source, regardless of intrinsic extent. This has serious implications on how we interpret morphological results for increasingly large photometric samples of LRDs, especially at extremely high-$z$ or in relatively shallow fields. We present results of Sersic and two-component fitting to a sample of observed LRDs to compare with our mock sample fitting. We find that $\sim85\%$ of observed LRDs are PSF-dominated, consistent with the AGN-dominated interpretation. The remaining $\sim15\%$ have low estimated PSF fractions (two-component fit) and sizes $\gtrsim 150$ pc (Sersic). This morphological diversity of LRDs suggests that that the population likely is not homogeneous. It possibly has a primary subset of sources consistent with the AGN-dominated hypothesis, and a secondary population of sources more consistent with arising perhaps from extremely compact starbursts.

Understanding how exoplanet atmospheres evolve is a key question in the context of habitability. One key process governing this evolution is atmospheric evaporation by stellar X-ray and EUV emission (collectively, XUV). As such, the evolution of exoplanet atmospheres is closely tied to the evolution of the host star's magnetic activity. Many studies have modelled the combined evolution of exoplanet atmospheres and their host stars. However, to date, the impact of the host star's metallicity on stellar activity/exoplanet atmosphere evolution has not been explored. In this work, we investigate how stellar metallicity affects the rotation and activity evolution of solar-like stars as well as the corresponding exoplanet atmospheric evolution. We reconfirm previous results that metal-rich stars spin down more rapidly than metal-poor stars. We also find that the XUV flux that an exoplanet in the habitable zone of its host star receives is larger when the host star is more metal-rich. As such, the atmospheres of exoplanets in the habitable zones of metal-rich stars are evaporated more rapidly than exoplanets in the habitable zones of metal-poor stars. Lastly, we find that the atmospheric evolution is most sensitive to the host star metallicity when the host star has a higher mass. In the highest mass solar-stars, the metallicity can have a larger influence on the atmospheric evolution than the initial rotation period of the star.

Hydrodynamic simulations can connect outflow observables to the physical conditions of outflowing gas. Here, we use simulations of isolated disk galaxies ranging from dwarf mass ($M_{200} = 10^{10}\mathrm{M}_{\odot}$) to Milky Way mass ($M_{200} = 10^{12}\mathrm{M}_{\odot}$), based on the FIRE-2 subgrid models to investigate multiphase galactic outflows. We use the CHIMES non-equilibrium chemistry module to create synthetic spectra of common outflow tracers ([CII]$_{158\rm{\mu m}}$, $\mathrm{CO}_{J(1-0)}$, H$\alpha$ and $[\mathrm{OIII}]_{5007\text{A}}$). Using our synthetic spectra we measure the mass outflow rate, kinetic power and momentum flux using observational techniques. In [CII]$_{158\rm{\mu m}}$ we measure outflow rates of $10^{-4}$ to $1$ $\mathrm{M_{\odot}yr^{-1}}$ across an SFR range of $10^{-3}$ to $1$ $\text{M}_{\odot}\text{yr}^{-1}$, which is in reasonable agreement with observations. The significant discrepancy is in $\mathrm{CO}_{J(1-0)}$, with the simulations lying $\approx1$ dex below the observational sample. We test observational assumptions used to derive outflow properties from synthetic spectra. We find the greatest uncertainty lies in measurements of electron density, as estimates using the SII doublet can overestimate the actual electron density by up to 2 dex, which changes mass outflow rates by up to 4 dex. We also find that molecular outflows are especially sensitive to the conversion factor between CO luminosity and H2 mass, with outflow rates changing by up to 4 dex in our least massive galaxy. Comparing the outflow properties derived from the synthetic spectra to those derived directly from the simulation, we find that [CII]$_{158\rm{\mu m}}$ probes outflows at greater distances from the disk, whilst we find that molecular gas does not survive at large distances within outflows within our modestly star-forming disk galaxies simulated in this work.

AT2018cqh is a unique optical tidal disruption event (TDE) discovered in a dwarf galaxy exhibiting delayed X-ray and radio flares. We present the results from high-resolution VLBA and e-MERLIN radio observations of AT2018cqh extending to $\delta$t $\sim$ 2250 days post discovery, which reveal a compact radio emission, unresolved at a scale of <~ 0.13 pc at 7.6 GHz, with a high brightness temperature of $T_b$ ~> 4.03 $\times$ 10$^{9}$ K. The radio spectral energy distribution (SED) is found to gradually shift towards a higher peak flux density and frequency over a period of $\sim$1000 days. An equipartition analysis suggests that there is a little change in the radio emitting region over this period, while the electron density increases by a factor of 3. The radio light curve at 0.89 GHz continues to rise, with a bump feature lasting for 240 days. These properties are in contrast to the predictions of standard shockwave model from a diffuse circumnuclear medium, but could be explained if dense clouds exist in the circumnuclear environment. The latter scenario is supported by our hydrodynamic simulations of the interaction of TDE outflow with a cloud, which can reproduce the temporal evolution in the radio SED. This work highlights the importance of the outflow-cloud interaction in explaining the delayed, fast-rising radio emission observed in some TDEs, especially those occurring in galaxies with pre-existing AGN activity.

We present the white dwarf catalog derived from the third data release of the Javalambre Photometric Local Universe Survey (J-PLUS DR3), which covers 3284 deg2 using 12 optical filters. A particular focus is given to the classification of outlier sources. We applied a Bayesian fitting process to the 12-band J-PLUS photometry of white dwarf candidates from Gaia EDR3. The derived parameters were effective temperature, surface gravity, and parallax. We used theoretical models from H- and He-dominated atmospheres, with priors applied to parallax and spectral type. From the posteriors, we derived the probability of an H-dominated atmosphere and of calcium absorption for each source. Outliers were identified as sources with chi2 > 23.2, indicating significant deviations from the best-fitting model. We analyzed the residuals from the fits using the UMAP technique, which enables the classification of outliers into distinct categories. The catalog includes 14844 white dwarfs with r < 20 mag and 1 < parallax < 100 mas, with 72% of the sources lacking spectroscopic (R > 500) classification. The application of UMAP identified three main types of outliers: random measurement fluctuations (391 sources), metal-polluted white dwarfs (98 sources), and two-component systems (282 sources). The last category also includes white dwarfs with strong carbon absorption lines. We validated the J-PLUS classifications by comparison with spectroscopy from SDSS and DESI, and with Gaia BP/RP spectra, confirming a one-to-one correspondence between J-PLUS photometric and spectroscopic classifications. The J-PLUS DR3 white dwarf catalog provides a robust dataset for statistical studies. The use of dimensionality reduction techniques enhances the identification of peculiar objects, making this catalog a valuable resource for the selection of interesting targets such as metal-polluted white dwarfs or binary systems.

The Fermi Large Area Telescope (LAT) has revealed a mysterious extended excess of GeV gamma-ray emission around the Galactic Center, which can potentially be explained by unresolved emission from a population of pulsars, particularly millisecond pulsars (MSPs), in the Galactic bulge. We used the distributed volunteer computing system Einstein@Home to search the Fermi-LAT data for gamma-ray pulsations from sources in the inner Galaxy, to try to identify the brightest members of this putative population. We discovered four new pulsars, including one new MSP and one young pulsar whose angular separation to the Galactic Center of 0.93° is the smallest of any known gamma-ray pulsar. We demonstrate a phase-resolved difference imaging technique that allows the flux from this pulsar to be disentangled from the diffuse Galactic Center emission. No radio pulsations were detected from the four new pulsars in archival radio observations or during the MPIfR-MeerKAT Galactic Plane Survey. While the distances to these pulsars remain uncertain, we find that it is more likely that they are all foreground sources from the Galactic disk, rather than pulsars originating from the predicted bulge population. Nevertheless, our results are not incompatible with an MSP explanation for the GC excess, as only one or two members of this population would have been detectable in our searches.

The detection of very high-energy gamma-rays from M87 can provide crucial insights into particle acceleration and radiation mechanisms in jets. The recent observations by the Large High Altitude Air Shower Observatory (LHAASO) detector extend the energy range of TeV gamma-ray astronomy, and also the variability study to the TeV energy domain. We have modelled the low state and flare state multi-wavelength spectral energy distributions of M87 within a time-dependent framework. In our model, the low state gamma-ray flux results from the emissions from the sub-parsec and the kilo-parsec scale jets of M87, whereas the flare state gamma-ray flux is mainly produced in the sub-parsec scale jet. We have shown that the spectral and temporal features of the TeV gamma-ray spectrum of M87 are consistent with this two-zone model, where the contribution from the sub-parsec scale jet significantly increases during the flare state.

We report the first calculation of light scattering on heavy dark matter (DM) particles. We show that despite the fact that DM has no direct coupling to photons, the light-DM($\gamma\chi$) ($m_\chi \sim 1$ TeV) cross-section is non-vanishing, albeit small. The cross section, calculated within the Standard Model (SM) framework, is particularly large in the case of heavy Weakly Interacting Massive Particles (WIMP). Combined with astrophysical observation, these results can constrain existing WIMP DM models in favor of lighter DM, $M_\chi<<M_{\mathrm{Planck}}$, (axions, composite DM, etc..) or non-weakly interacting pure gravitational DM. We also show that the energy dependence of light scattering on dark matter should make the DM colored - red in the case of weak-DM and blue for the gravitational-DM, when a white background light is passing through. Gravitational scattering of light on DM particles also leads to non-trivial polarization effects, which might be easier to detect than the deflection of light from the scattering on DM particles, $\gamma\chi\rightarrow\gamma\chi$.

Black holes (BHs) with synchronized bosonic hair challenge the Kerr paradigm, linking superradiance from ultralight fields -- creating gravitational atoms -- to bosonic stars across parameter space. In the ''very hairy'' regime, where a small horizon lies inside a bosonic star containing most of the energy, they deviate sharply from Kerr, but their dynamics remain unexplored. We show that for such solutions the horizon gets naturally ejected from the center of its scalar environment, and observe a similar dynamics in a cousin model of BHs with resonant scalar hair, albeit with a different fate. This dynamical splitting is likely to be generic for sufficiently hairy BHs in the broader class of models with synchronized or resonant hair, but possible exceptions may exist.

We develop a relativistically accurate formalism to model the interaction between stellar mass compact objects embedded in thin accretion disks around a non-spinning supermassive black hole, using tools from self-force theory and Hamiltonian perturbation theory. We then apply this formalism to analyze the evolution of a compact object on a nearly circular and equatorial orbit interacting with a thin equatorial disk. We provide analytic and relativistically-accurate expressions for the rates of energy and angular momentum exchanged during interactions due to Lindblad and corotation resonances. Our results show that relativistic corrections can enhance the magnitude of the torque by 1-2 orders of magnitude compared to purely Newtonian expressions when the orbit of the compact object is smaller than $10$ Schwarzschild radii of the supermassive black hole. We also demonstrate that strong relativistic shifts the inner Lindblad resonances closer to the compact object than the outer Lindblad resonances when the compact object is closer than 4 Schwarzschild radii to the supermassive black hole, potentially leading to a reversal in the direction of the torque acting on the compact object. Finally, we provide a dephasing estimate and show that using the relativistic torque formula is crucial to obtain reliable estimates for extreme mass ratio inspirals in orbits closer than 5 Schwarzschild radii to the supermassive black hole. Our results highlight the importance of using relativistically-accurate models of environmental interactions in extreme mass-ratio inspirals close to a supermassive black hole.

We propose a novel collider probe of baryogenesis at TeV scale by measuring decay asymmetries into particle and anti-particle final states. Motivated by the idea of Dirac leptogenesis, we consider an extension of the standard model with new colored and $SU(2)_L$ singlet particles in such a way that the out-of-equilibrium decay of heavy colored fermions creates equal and opposite CP asymmetries in two sectors, prevented from equilibrating with each other. While the TeV scale viability of this mechanism requires a resonantly enhanced CP asymmetry, the latter also plays a crucial role leading to observable decay asymmetries in colliders. In addition to discussing conventional signatures of such heavy colored particles, namely, mono-jet plus missing transverse energy, displaced vertex, colored track at hadron colliders, we also show the unique possibility of measuring decay asymmetries via forward-backward and charge asymmetries at future muon colliders. In addition to being a verifiable TeV-scale baryogenesis scenario, the model also predicts a singlet scalar dark matter candidate consistent with the required thermal dark matter properties near the Higgs resonance.

We present a passive ultraviolet charge management system for the fused silica test masses in ground-based laser interferometric gravitational wave detectors. The system uses photoelectron emission from low work-function gold coatings illuminated by 275 to 285 nm UV light to neutralize unwanted electric charges on the electrically floating test masses, maintaining them at zero potential relative to surrounding components. Two implementation schemes are described: 1. distributed discharge tabs illuminated by UV LEDs mounted at the eight surrounding earthquake stops, and 2. a conductively linked tab design enabling a centralized discharge on the test mass barrel, with potential extension to annular coatings around the high-reflectivity and anti-reflective surfaces. Experimental results show photoelectric currents greater or equal to 10 pA for 1.0 mW of incident UV, enabling discharge rates greater than 10V/s for a 1 pF capacitance. With 0.2 mW UV power, charge neutralization to less or equal to 1 pC can be achieved in 5 to 75 minutes. This technique offers a vacuum-compatible alternative to ion sprayers, significantly reducing operational downtime. For the conductive-barrel configuration, we also propose a balanced electrostatic actuator using four parallel-plate capacitors for combined control of TM axial displacement, tilt, and azimuth, with reduced drive voltages.

We demonstrate that in pair plasma weakly nonlinear electromagnetic waves, $a_0 \leq 1$, experience Anderson self-localization. The beat between the driver and a back-scattered wave creates random, charge-neutral, large density fluctuations $\delta \rho/\rho \gg 1$, and corresponding random fluctuations of the dielectric permittivity $\epsilon$. Propagating in quasi-1D, waves in a medium with spatially random, time-varying, self-created fluctuations of dielectric permeability experience localization. Anderson self-localization of light leads to (i) reflection of EM waves by the under-dense pair plasma; (ii) a wave already present inside the plasma separates into bright trapped pockets and dark regions. Mild initial thermal spread restores wave propagation by suppressing the seeds of parametrically unstable density fluctuations. A circularly polarized driver produces linearly polarized structures, with position angle varying randomly between the bright pulses. We discuss possible applications to astrophysical Fast Radio Bursts.

Suspension thermal modes in interferometric gravitational-wave detectors produce narrow, high-Q spectral lines that can contaminate gravitational searches and bias parameter estimation. In KAGRA, cryogenic mirrors are held by thick suspension fibers, designed to sustain such low-temperature environment, which may further affects inharmonicity modes, fiber dimensions, and mechanical behavior compared to typical interferometers. Remaining a prominent source of narrowband contamination, we implement a Kalman filter to model and track violin lines, building on the methodology introduced in [1], and apply subtraction to KAGRA O3GK data. Using gravitational-wave template injections, we validate that the subtraction preserves matched-filter SNR while effectively suppressing line power. Comparisons of power spectral densities and residual analyses confirm that the method removes deterministic line contributions without introducing waveform distortions. This approach provides a cleaner strain channel for searches and parameter estimation and will become increasingly important for future low-temperature detectors with higher-Q suspensions, such as the Einstein Telescope.

One of the key features of the $R^2$-gravity is the embedding of a scalar field, scalaron, into the gravity sector. The scalaron interacts with the Standard Model (SM) matter fields through Planck-suppressed couplings. If the scalaron serves as a viable dark matter (DM) candidate, it can account for the lack of evidence of DM interactions beyond gravity in experimental and observational probes to date. The realization of the scalaron, as a cold DM candidate, depends on an induced trilinear interaction with the SM Higgs, despite its suppressed coupling strength. Here, we introduce a Higgs non-minimal coupling to gravity that additionally contributes to the induced trilinear interaction with its existing competing part, originated from the $R^2$-gravity. We study the interplay between these two contributions in the early universe, which determines both the initial conditions and evolution of the scalaron, leading to cold DM behavior at a later epoch. The trilinear interaction vanish identically for certain combinations of the Higgs non-minimal coupling and the scalaron mass, thereby setting the scalaron density through misalignment mechanism, similar to axions. Consequently, we find that the observed DM relic density is obtained for a scalaron mass between $1.38$ keV and $0.7$ MeV. The lower limit on the mass stems from the LHC constraints on the Higgs non-minimal coupling, whereas the upper bound arises from INTEGRAL/SPI limits on the excess gamma-ray flux from possible scalaron decays to two photons.

We investigate the gravitational-wave background predicted by a two-scalar-field cosmological model that aims to unify primordial inflation with the dark sector, namely late-time dark energy and dark matter, in a single and self-consistent theoretical framework. The model is constructed from an action inspired by several extensions of general relativity and string-inspired scenarios and features a non-minimal interaction between the two scalar fields, while both remain minimally coupled to gravity. In this context, we derive the gravitational-wave energy spectrum over wavelengths ranging from today's Hubble horizon to those at the end of inflation. We employ the continuous Bogoliubov coefficient formalism, originally introduced to describe particle creation in an expanding Universe, in analogy to the well-established mechanism of gravitational particle production and, in particular, generalized to gravitons. Using this method, which enables an accurate description of graviton creation across all cosmological epochs, we find that inflation provides the dominant gravitational-wave contribution, while subdominant features arise at the inflation-radiation, radiation-matter, and matter-dark energy transitions, i.e., epochs naturally encoded inside our scalar field picture. The resulting energy density spectrum is thus compared with the sensitivity curves of the planned next-generation ground- and space-based gravitational-wave observatories. The comparison identifies frequency bands where the predicted signal could be probed, providing those windows associated with potentially detectable signals, bounded by our analyses. Consequences of our recipe are thus compared with numerical outcomes and the corresponding physical properties discussed in detail.

We investigate the possibility of using the cosmic gravitational focusing (CGF) to probe the minor light dark matter (DM) component whose mass is in the range of $(0.1 \sim 100)$\,eV. Being a purely gravitational effect, the CGF offers a mode-independent probe that is complementary to the existing ways such as Lyman-$\alpha$ and $\Delta N_{\rm eff}$. Such effect finally leads to a dipole density distribution that would affect the galaxy formation and hence can be reconstructed with galaxy surveys such as DESI. Both the free-streaming and clustering limits have been studied with analytical formulas while the region in between is bridged with interpolation. We show the projected sensitivity at DESI with the typical phase space distribution of a freeze-in DM scenario as illustration.

We construct $F(R)$ gravity models with scalar fields to describe cosmological inflation and formation of primordial black holes (PBHs). By adding the induced gravity term and the fourth-order polynomial potential for the scalar field to the known $F(R)$ gravity model, and using a conformal transformation of the metric, we obtain a two-field chiral cosmological model. For some values of the model parameters, we get that the inflationary parameters of this model are in good agreement with the observations of the cosmic microwave background radiation obtained by the Atacama Cosmology Telescope. The estimation of PBH masses suggests that PBHs could be dark matter candidates.