Sazuna/UAT_keywords huggingface dataset:
The Impact of Ram Pressure on the Radio Spectral Index and Magnetic Field of NGC 4522: A High-resolution VLA Continuum Study. We present high-resolution Very Large Array continuum observations at the S band (3 GHz, 560 pc scale) and X band (10 GHz, 200 pc scale) of the ram-pressure-stripped Virgo galaxy NGC 4522 to investigate the characteristics of its radio continuum, spectral index, and magnetic field under the influence of the intracluster medium (ICM). The total radio continuum shows an asymmetry that extends northwest, mirroring the H I gas distribution but showing distinct features in the extraplanar regions. The spectral index steepens systematically from α ∼ −0.6 in the main disk to α ∼ −1.1 in the outer disk. We find that the spectral index behavior of the outer disk is mainly due to an ICM shock that can reaccelerate electrons and a significant reduction of thermal emission. Intriguingly, extraplanar clouds exhibit exceptionally flat spectral indices (α ∼ −0.2 to 0), resulting from a combination of significantly enhanced thermal emission and pronounced spectral aging of the nonthermal component. Although some of these regions correlate with Hα, others do not. We propose that the mixing between the ICM and interstellar medium (ISM) is an alternative mechanism that enhances thermal emission independently of star formation. Polarized continuum emissions are highly asymmetric, preferentially distributed along the ICM wind side, and the polarization fraction increases radially outward from the galactic midplane, indicating that the polarized emission is strongly influenced by the ICM wind. Our results show how and where the ICM substantially affects the ISM and also demonstrate that high-frequency observations are crucial for analyzing the radio continuum of ram pressure stripping galaxies.

Keywords: Galaxy clusters, Interstellar medium, Radio continuum emission, Spectral index, Radio interferometry, Galaxies, Extragalactic magnetic fields
Coherence of Supermassive Black Hole Binary Demographics with the nHz Stochastic Gravitational-wave Background. We present a refined estimation of the stochastic gravitational-wave background (SGWB) based on observed dual active galactic nuclei (AGNs) together with AGN X-ray luminosity functions, in light of recent Pulsar Timing Array (PTA) detections of an nHz SGWB. We identify a characteristic luminosity dependence in dual AGN fractions by compiling recent observational data sets, providing crucial constraints on supermassive black hole binary (SMBHB) populations. Our AGN-based model reproduces the current SGWB measurements within PTA observational uncertainties of 2σ─4σ, demonstrating consistency between electromagnetic and gravitational-wave observations. These findings establish SMBHBs as the dominant source of the nHz gravitational-wave signal, providing crucial insights into their demographics and evolution.

Keywords: Double quasars, Supermassive black holes, Gravitational wave sources, Active galactic nuclei, Gravitational waves
A Census of Star-formation and Gas Mass Tracers in Two Lensed z ∼ 4 Dusty Star-forming Galaxies. We present new and archival Atacama Large Millimeter/submillimeter Array observations of two strongly lensed dusty star-forming galaxies (DSFGs) selected from the South Pole Telescope survey, SPT0418-47 (z = 4.225) and SPT2147-50 (z = 3.760). We study the [C II], CO(7─6), [C I](2─1), and, in SPT0418-47, p─H2O emission, which, along with the underlying continuum (rest-frame 160 and 380 μm), are routinely used as tracers of gas mass and/or star-formation rate (SFR). We perform a pixel-by-pixel analysis of both sources in the image plane to study the resolved Kennicutt─Schmidt relation, finding generally good agreement between the slopes of the SFR versus gas mass surface density using the different tracers. Using lens modeling methods, we find that the dust emission is more compact than the line emission in both sources, with CO(7─6) and [C I](2─1) similar in extent and [C II] the most extended, reminiscent of recent findings of extended [C II] spatial distributions in galaxies at similar cosmic epochs. We develop the [C I](2─1)/ CO(7─6) flux-density ratio as an observable proxy for gas depletion timescale (τdep), which can be applied to large samples of DSFGs, in lieu of more detailed inferences of this timescale, which require analysis of observations at multiple wavelengths. Furthermore, the extended [C II] emission in both sources, compared to the total continuum and line emission, suggests that [C II], used in recent years as a molecular gas mass and SFR tracer in high-z galaxies, may not always be a suitable tracer of these physical quantities.

Keywords: Star formation, Submillimeter astronomy, Strong gravitational lensing, High-redshift galaxies
Cloud─Cloud Collisions Induce Filament-mediated Super Star Cluster Formation in the Antennae Overlap Region: Evidence from ALMA and JWST. The formation of super star clusters (SSCs) in galaxies remains a fundamental yet unresolved problem. Among the proposed mechanisms, cloud─cloud collisions (CCCs) have been suggested as a potential trigger, although observational validation has been limited. Here we present high-resolution ( 0.″12 , ∼14 pc) Atacama Large Millimeter/submillimeter Array observations of CO (J = 1─0) emission toward a super giant molecular cloud (SGMC) in the overlap region of the Antennae galaxies. The data resolve the SGMC into two distinct velocity components separated by ∼50 km s−1. One component exhibits a "U"-shaped structure within a large filament likely shaped by ram pressure, while the other shows hub-filament morphology. Such a morphology is naturally interpreted as a CCC scenario. The 108 GHz continuum emission detected at the apparent collision interface is dominated by free─free radiation, with an ionizing photon rate consistent with the stellar mass and age of the optically identified SSCs. Supplementary infrared imaging with JWST reveals emission spatially coincident with the inferred collision interface, further supporting the CCC scenario. These results provide compelling, multiwavelength evidence that CCCs play a key role in triggering SSC formation in merging galaxies.

Keywords: Starburst galaxies, Galaxy collisions, Millimeter astronomy, Star forming regions, Galaxy interactions, Young star clusters, Molecular clouds, Interstellar clouds, Galaxy mergers, Extragalactic astronomy
Ne and Fe Abundances in the Interstellar Medium: Archival Study of Fe-L and Ne-K Edges in Chandra and XMM-Newton. The abundance of elements in the interstellar medium is a key facet for many fields of astrophysical study. In the soft X-ray spectra, absorption by interstellar gas can result in deep absorption features that affect continuum measurements. In this paper, we focus on measuring the abundance of interstellar iron and neon from the column densities observed in soft spectra from XMM-Newton and Chandra for various low-mass X-ray binaries, which allows for a direct probe of elemental abundances. As a noble gas, neon will not deplete into solid form, thus providing a benchmark with abundances determined via UV spectroscopy. We find that, when assuming Fe is 90% depleted into grains, [Fe/Ne] = −0.523 ± 0.025, [Fe/H]+12 = 7.482 ± 0.016, and [Ne/H]+12 = 8.012 ± 0.022, which are the tightest observational constraints on these abundances to date, while being consistent with the literature, which uses protosolar abundances. We also test how depletion into solid grains and scattering affect the results. The choice of depletion fraction can affect the abundance measurement by roughly 5%, and the inclusion of a scattering component can affect abundance measurements by ∼1%─7%.

Keywords: Low-mass x-ray binary stars, Interstellar medium
Equatorially Asymmetric Magnetic Fields and Their Impact on Black Hole Accretion Dynamics. We investigate the impact of equatorial asymmetry in the magnetic field geometry on accretion dynamics around a spinning black hole using axisymmetric general relativistic magnetohydrodynamic simulations. We consider a Fishbone─Moncrief torus orbiting a Kerr black hole with spin parameter a = 0.9375, threaded by large-scale magnetic fields that are asymmetric about the equatorial plane. The degree of equatorial asymmetry in the magnetic field is parameterized by an angle, with values of 30°, 45°, and 60°. We examine how this equatorially asymmetric initial magnetic field configuration influences the magnetic field structure, accretion flow morphology, and angular momentum transport across a range of initial plasma beta values (β = 0.007, 0.005, 0.001). We find that such deformation in the magnetic field leads to noticeable changes in the inner disk structure, asymmetric outflow patterns in the poloidal plane, and time-dependent variations in accretion rates. These effects are generally more pronounced at lower beta values, where magnetic pressure dominates; in particular, the 30° case at β = 0.001 exhibits strong and persistent asymmetric inflows and outflows. Our results demonstrate that equatorially asymmetric magnetic field configurations can significantly influence the structure and variability of relativistic accretion flows. These findings motivate future extensions to full three-dimensional studies, where black hole magnetospheres can be explored in a more general setting.

Keywords: Black hole physics, High energy astrophysics, Relativistic jets, Astrophysical fluid dynamics, Magnetohydrodynamical simulations
The Periastron Passage of T Tauri South B as Viewed by ALMA: Millimeter Flux Variations and Dust Heating Triggered by Orbital Motion. We present 225 and 350 GHz imaging of the iconic T Tauri system using the Atacama Large Millimeter submillimeter Array (ALMA). T Tauri is a hierarchical triple system, and the close binary T Tau Sa/Sb underwent periastron passage in 2023 March. The ALMA images were obtained in epochs spanning 2019 November through 2023 June, and therefore covered the time frame of the recent periastron passage. We clearly resolve the Sa─Sb binary in two epochs of high-resolution measurements with ALMA. We find increases in millimeter flux from heating of the Sa disk and the wider distribution of dust in the environment of the binary. This heating is likely in response to increased stellar accretion activity triggered by orbital motion during the dynamic periastron passage of T Tau Sb around Sa. Resolved, extended millimeter emission is also found to change morphology and increase in flux in the immediate environment of the Sa─Sb binary after periastron passage. This may suggest an increase in nonthermal emission from magnetic interaction, gravitational disruption of the circumstellar disks as the stars passed through periastron, or both of these phenomena. We also detected structures in the compact (24 au radius), thermal dust disk around T Tau N. In particular, we identify a crescent-shaped emission excess just outside a shallow gap at 12 au radius that appears to move at Keplerian speed. Future measurement of dust spectral indices can clarify the origin of increased and variable millimeter emission in the environment of the T Tau S binary.

Keywords: T Tauri stars, Binary stars, Orbital motion, Circumstellar disks
Envelope Inflation and Outflow Driven by Energy Deposition in Massive Stars. Evolved massive stars are known to undergo outflow with high-mass ejections, resulting in the loss of a substantial portion of their envelopes. One proposed mechanism driving these events is the release or deposition of energy within the stellar envelope. We use a one-dimensional hydrodynamical code to investigate the resulting outflow and stellar response to energy deposition at specific regions inside a 70 M⊙ star. We compare hydrostatic and hydrodynamic models and test for different energies and widths of the depositing region. We find that due to the deposited energy, the envelope expands significantly, and under certain conditions, such as assuming a uniform electron scattering opacity, this energy input becomes sufficient to unbind material from the outer envelope. This, in turn, leads to the formation of an outflow. We find that higher deposited energy triggers a strong outflow and results in a somewhat hotter and less expanded envelope due to the rapid loss of energy through expelled material. This driving mechanism leads to sudden envelope expansion and the formation of strong outflows in our models, highlighting the generic hydrodynamic response of massive star envelopes to impulsive energy input.

Keywords: Massive stars, Luminous blue variable stars, Stellar mass loss, Stellar winds, Stellar evolution
Rise of the Forsaken Relics: Connecting Present-day Stellar Streams and Phase-mixed Galaxies to the Epoch of Reionization. The "near─far" approach to studying reionization leverages the star formation histories of the Milky Way (MW) or Local Group (LG) galaxies, derived from resolved photometry, to infer the low-mass/faint end of the stellar mass functions (SMFs) or the ultraviolet luminosity functions (UVLFs) of high-redshift galaxies (z ≳ 6), beyond the current James Webb Space Telescope detection limits (MUV ≳ −15). Previous works considered only intact low-mass galaxies in the MW and LG, neglecting disrupted galaxies such as stellar streams and phase-mixed objects. Using the FIRE-2 simulations, we show that these disrupted galaxies contribute up to ∼50% of the total stellar-mass budget of the proto-MW/LG at z = 6−9. Including all the progenitors of these disrupted galaxies improves the normalization of the recovered SMFs/UVLFs by factors of ∼2─3 and reduces the halo-to-halo variation in the slope by ∼20%─40%. This enables robust constraints down to at least the resolution limit of the simulations, near M⋆ ∼ 105M⊙or MUV ∼ −10 at z ≳ 6. We also show that "fossil-record" reconstructions—which assume each present-day system descends from a single reionization-era progenitor—are sensitive to the stellar-mass/UV-magnitude thresholds, which introduces bias in the inferred slopes at the low-mass/faint end. Additionally, we demonstrate that neglecting disrupted systems underestimates the contribution of galaxies with MUV ≲ −15 to the reionization-era UV luminosity density. Finally, we estimate that a significant fraction (∼50%) of streams with M⋆ ≳ 106M⊙ at z = 0 should be detectable from upcoming Rubin Observatory and Roman Space Telescope observations.

Keywords: Local Group, Stellar streams, Galaxy evolution, Reionization, High-redshift galaxies, Milky Way Galaxy
First Resolution of a Main-sequence G star's Astrosphere Using Chandra. We report the resolution of a halo of X-ray line emission surrounding the zero-age main-sequence G8.5V star HD 61005 by Chandra/ACIS-S. Located only ∼36 pc distant, HD 61005 is young (100 ± 50 Myr) and X-ray bright (∼300 × solar), observed with a nearly edge-on geometry and surrounded by very local interstellar medium (VLISM) material denser than in the Sun's environs. HD 61005 is known to harbor large amounts of circumstellar dust in a dense ecliptic plane full of millimeter-sized particles plus attached, extended "Wing like structures" full of micron-sized particles, which are evidence for strong VLISM─dust disk interaction. These properties aided our ability to resolve the system's ∼220 au wide astrosphere, the first ever observed for a main-sequence G star. The observed X-ray emission morphology is roughly spherical, as expected for an astrospheric structure dominated by the host star. The Chandra spectrum of HD 61005 is a combination of a hard stellar coronal emission (T ∼ 8 MK) at LX ∼ 6 × 1029 erg s−1, plus an extended halo contribution at LX ∼ 1 × 1029 erg s−1 dominated by charge exchange (CX) lines, such as those of O VIII and Ne IX. The Chandra CX X-ray morphology does not track the planar dust morphology but does extend out roughly to ∼110 au where the base of the dust wings begins. We present a toy model of the astrosphere emission produced by stellar wind─VLISM CX interactions, similar to the state of the young Sun when it was only ∼108 yr old and transiting through an ∼103 times denser part of the interstellar medium (such as a giant molecular cloud).

Keywords: X-ray astronomy, Stellar-interstellar interactions, Heliosphere, Astrosphere interstellar medium interactions, Stellar phenomena, Charge exchange recombination, Interstellar medium wind
B-field Orion Protostellar Survey (BOPS). IV. The Relative Orientation between Magnetic Fields and Density Structures in Young Protostellar Envelopes. We investigate the relative alignment between density structures and magnetic fields in eight young protostars from the Atacama Large Millimeter/submillimeter Array B-field Orion Protostellar Survey. Column density maps are derived from 870 μm dust continuum emission, and the Histogram of Relative Orientations method is applied to quantify the correlation between magnetic field orientations and density structures on envelope scales (∼103 au). We find that the relative alignment shows overall little evidence of systematic evolution with column density, suggesting that column density alone does not fully determine the alignment. The magnetization level also plays a crucial role, with weakly magnetized envelopes exhibiting predominantly parallel or random alignment, whereas strongly magnetized ones show perpendicular configurations even at moderate densities. These results reveal that density and magnetization jointly shape the morphology of protostellar envelopes and the coupling between gravity and magnetic fields during early stages of star formation.

Keywords: Interstellar magnetic fields, Circumstellar envelopes, Star forming regions, Star formation
GW231123: Likely a Product of Successive Mergers from ∼10 Stellar-mass Black Holes. GW231123 is an exceptionally massive binary black hole (BBH) merger with unusually high component spins. Such extreme properties challenge conventional stellar evolution models, predicting a black hole (BH) mass gap due to pair-instability supernovae. We test possible formation scenarios for GW231123 using population-informed priors on BH spin distributions, in light of population properties built on the previous (GWTC-3) data. Our analysis shows that GW231123 belongs to the high-spin subpopulation that is naturally interpreted as hierarchical BBH mergers. By comparing the spin magnitudes and component masses of GW231123 to those of the remnants of previous mergers, we show that both components of GW231123 are multigeneration (&gt;2G) merger remnants, and plausibly originated from the successive mergers of ∼6 and ∼4 first-generation BHs, respectively. This suggests that repeated mergers can be frequent, and even more massive intermediate-mass BHs may be produced. Thus, mechanisms that can efficiently harden the BBHs' orbits are required, e.g., gas dynamical friction in the disks of active galactic nuclei.

Keywords: Intermediate-mass black holes, Stellar mass black holes, Astrophysical black holes, Black holes
X-Ray Polarization of the Intrabinary Shock in Redback Pulsar J1723−2837. The intrabinary shocks (IBSs) in spider pulsars emit nonthermal synchrotron X-rays from accelerated electrons and positrons in the shocked pulsar wind, likely energized by magnetic reconnection. The double-peaked X-ray light curves from these shocks have been well characterized in several spider systems. In this paper, we analyze Imaging X-ray Polarimetry Explorer observations of the redback pulsar J1723−2837 to examine the expected synchrotron polarization. Using advanced extraction methods that include spatial, temporal, and particle background weights, we constrain the polarization of the IBS. We compare different models for the magnetic field in the radiation zone and find that the best fit prefers a striped pulsar wind model over other polarized models, with maximum polarization degree of the IBS emission component  ΠIBS=36−15+16% , in addition to an unpolarized non-IBS component. Since this is only 2.4σ, we cannot claim strong preference over an unpolarized model; we report a 99% confidence level upper limit on the total polarization of both IBS and non-IBS components Π99 &lt; 36%, which is improved over the 50% limit obtained in previous work. The best-fit polarization of the IBS component is consistent with numerical simulations. Detailed tests of such models are accessible to future measurements.

Keywords: Millisecond pulsars, Pulsars, Non-thermal radiation sources, Shocks, Binary pulsars
Dynamical Tide-modified Roche Limit in Eccentric, Asynchronous Binaries. The Roche limit, or the threshold separation within which a celestial object (the donor) M cannot remain in a stable configuration due to a companion's tidal field, has been well established when M is in hydrostatic equilibrium and has synchronous rotation in a circular orbit. However, limited analyses exist considering corrections to the Roche limit due to hydrodynamical effects. We fill in the gap by providing a general theoretical framework involving nonlinear hydrodynamics. We consider both exact nonlinear equations derived from an affine model describing incompressible ellipsoids and series-expanded ones that can be calculated for realistic stars and planets. Our formulation addresses the Roche problem in generic orbits and synchronization levels of M, and fully accounts for the history-dependent hydrodynamical effects. We show that, as the orbital eccentricity increases, fluid instability is more likely to develop at the pericenter due to the increased dynamical tide that accumulates over multiple orbits. When M moves in a highly eccentric orbit (with eccentricity around 0.9) and the damping of the fluid is small, the threshold pericenter separation at which mass loss from M can occur can be at least 30% higher than the value predicted for a circular orbit with hydrostatic equilibrium. If only a single passage is considered, however, the threshold separation is 20% smaller than the static limit. The nonlinear interaction at each pericenter passage can also trigger a diffusive fluid evolution inside M even with moderate eccentricities, complementing previous studies of diffusive tides caused by random propagation phases. Our work has broad implications for interacting binaries in eccentric orbits, including migrating gaseous exoplanets, repeated partial tidal disruption events, and more.

Keywords: Exoplanet dynamics, Hydrodynamics, Tidal disruption, Roche limit, Exoplanet tides, X-ray transient sources