Sazuna/UAT_keywords huggingface dataset:
SAGAbg. III. Environmental Stellar Mass Functions, Self-quenching, and the Stellar-to-halo Mass Relation in the Dwarf Galaxy Regime. Recent efforts have extended our view of the number and properties of satellite galaxies beyond the Local Group firmly down to M⋆ ∼ 106M⊙. A similarly complete view of the field dwarf population has lagged behind. Using the background galaxy sample from the Satellites Around Galactic Analogs (SAGA) survey at z &lt; 0.05, we take inventory of the dwarf population down to M⋆ ∼ 5 × 106M⊙ using three metrics: the stellar mass function (SMF) as a 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 α1 = −1.44 ± 0.09 down to M⋆ ∼ 5 × 106M⊙, and that the quenched fraction of isolated dwarfs drops monotonically to fq ∼ 10−3 at M⋆ ∼ 108.5M⊙. Though slightly steeper than estimates from H I 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 SAGAbg-SMF SHMR, we find that big-box cosmological simulations largely overpredict isolated galaxy quenched fractions via a turnaround in fq(M⋆) at 108 ≲ M⋆/M⊙ ≲ 109, underscoring the complexities in disentangling the drivers of galaxy formation and the need for systematic multidimensional observations of the dwarf population across environments.

Keywords: Stellar mass functions, Galaxy dark matter halos, Dwarf galaxies, Quenched galaxies
WALLABY Pilot Survey: Characterizing Low-rotation Kinematically Modeled Galaxies. Many of the tensions in cosmological models of the Universe lie in the low-mass, low-velocity regime. Probing this regime requires a statistically significant sample of galaxies with well-measured kinematics and robustly measured uncertainties. The Widefield ASKAP L-band Legacy All-sky Blind surveY (WALLABY), as a wide-area, untargeted H I survey, is well positioned to construct this sample. As a first step toward this goal, we develop a framework for testing kinematic modeling codes in the low-resolution, low signal-to-noise ratio, low rotation velocity regime. We find that the WALLABY Kinematic Analysis Proto-Pipeline is remarkably successful at modeling these galaxies when compared to other algorithms, but, even in idealized tests, there is a significant fraction of false positives found below inclinations of ≍40°. We further examine the 11 detections with rotation velocities below 50 km s−1 in the WALLABY pilot data releases. We find that those galaxies with inclinations above 40° lie within 1σ─2σ of structural scaling relations that require reliable rotation velocity measurements, such as the baryonic Tully─Fisher relation. Moreover, the subset that has consistent kinematic and photometric inclinations tends to lie nearer to the relations than those that have inconsistent inclination measures. This work both demonstrates the challenges faced in low-velocity kinematic modeling and provides a framework for testing modeling codes as well as constructing a large sample of well-measured low-rotation models from untargeted surveys.

Keywords: Galaxy kinematics, Galaxies
ALMA-IMF. XX. Core Fragmentation in the W51 High-mass Star-forming Region. We present a study of core fragmentation in the W51-E and W51-IRS2 protoclusters in the W51 high-mass star-forming region. The identification of core fragmentation is achieved by the spatial correspondence of cores and compact sources, which are detected in the short- (low-resolution) and the long-baseline (high-resolution) continuum images from the Atacama Large Millimeter/submillimeter Array (ALMA) in Bands 3 (3 mm) and 6 (1.3 mm), respectively. We characterize the compact sources found in the long-baseline images, and conclude that the compact sources are pre-/protostellar objects (PPOs) that are either prestellar dust cores or dust disks or envelopes around protostars. The observed trend of core fragmentation in W51 is that (i) massive cores host more PPOs, (ii) bright PPOs are preferentially formed in massive cores, and (iii) equipartition of flux between PPOs is uncommon. The thermal Jeans masses of the parent cores are insufficient to explain the masses of their fragments, and this trend is more prominent for high-mass cores. We also find that unfragmented cores are large, less massive, and less dense than fragmented cores.

Keywords: Initial mass function, Millimeter astronomy, Star forming regions, Protoclusters, Star formation
Enhanced Pebble Drift across Planet-opened Gaps in Windy Protoplanetary Disks. When a giant planet forms in a protoplanetary disks, it carves a gap around its orbit separating the disk into two parts: an inner disk and an outer disk. Traditional disk accretion models, which assume material transport is driven by viscosity, reveal that the planet-induced gap acts like a filter which blocks large dust grains from flowing into the inner disk. However, there is growing evidence that material transport may be driven by magnetically driven winds instead. By carrying out a suite of two-dimensional multifluid hydrodynamic simulations where wind is implemented with a parameterized model, we explore how dust filtration efficiency and the size of dust grains filtered change in disks where gas accretion is dominated by magnetically driven winds. We find that the inward gas flow driven by the wind can enable dust to overcome the pressure bump at the outer gap edge and penetrate the planet-induced gap. The maximum size of dust grains capable of penetrating the gap increases with wind strength. Notably, we found that when wind is strong (mass-loss rate = 10−7 M⊙ yr−1), millimeter-sized grains can penetrate the gap opened by a multi-Jovian-mass planet. Our results suggest that magnetically driven winds can significantly enhance pebble drift and impact planet formation in the inner protoplanetary disk.

Keywords: Hydrodynamical simulations, Hydrodynamics, Planetary system formation, Protoplanetary disks, Planet formation
Galaxy Model Subtraction with a Convolutional Denoising Autoencoder. Galaxy model subtraction removes the smooth light of nearby galaxies so that fainter sources (e.g., stars, star clusters, and background galaxies) can be identified and measured. Traditional approaches (isophotal or parametric fitting) are semiautomated and can be challenging for large datasets. We build a convolutional denoising autoencoder (DAE) for galaxy model subtraction: images are compressed to a latent representation and reconstructed to yield the smooth galaxy, suppressing other objects. The DAE is trained on GALFIT-generated model galaxies injected into real sky backgrounds and tested on real images from the Next Generation Virgo Cluster Survey. To quantify performance, we conduct an injection-recovery experiment on residual images by adding mock globular clusters (GCs) with known fluxes and positions. Our tests confirm a higher recovery rate of mock GCs near galaxy centers for complex morphologies, while matching ellipse fitting for smooth ellipticals. Overall, the DAE achieves subtraction equivalent to isophotal ellipse fitting for regular ellipticals and superior results for galaxies with high ellipticities or spiral features. Photometry of small-scale sources on DAE residuals is consistent with that on ellipse-subtracted residuals. Once trained, the DAE processes an image cutout in ≲0.1 s, enabling fast, fully automatic analysis of large datasets. We make our code available for download and use.

Keywords: Globular star clusters, Convolutional neural networks, Dwarf galaxies, Astronomy data analysis, Astronomy image processing
Why Do Solar Wind Models Get It Wrong? Understanding the Capabilities of Time-dependent Solar Wind Simulations. We explore the capabilities of time-dependent (TD) magnetohydrodynamic (MHD) solar wind simulations with the coupled Wang─Sheeley─Arge (WSA) model of the solar corona and the Grid Agnostic MHD for Extended Research Applications model of the inner heliosphere. We compare TD with steady-state (SS) simulations and in situ observations from multiple spacecraft (Earth, STEREO-A, Parker Solar Probe). 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 1 year of TD predictions at the Earth and STEREO-A locations shows that tuning accordingly the WSA relationship when used with MHD models and 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 data can help mitigate this effect; however, unless we get a 4π view of the Sun, we will be unable to completely address it.

Keywords: Magnetohydrodynamics, Space weather, Solar wind, Solar physics, Interplanetary physics, Magnetohydrodynamical simulations
Ross 458 C: Gas Giant or Brown Dwarf?. Ross 458 C is a widely separated planetary mass companion at a distance of 1100 au from its host binary, Ross 458 AB. It is a member of a class of very low-mass companions at distances of hundreds to thousands of astronomical units from their host stars. We aim to constrain Ross 458 C's formation history by fitting its near-IR spectrum with models to constrain its composition. If its composition is similar to its host star, we infer that it likely formed through turbulent fragmentation of the same molecular cloud that formed the host. If its composition is enhanced in heavy elements relative to the host, this lends evidence to formation in the disk and subsequent migration to its current separation. Here, we present high-resolution (R ∼ 2700) emission spectra of Ross 458 C obtained with JWST NIRSpec's fixed slit in the F070LP, F100LP, and F170LP filters from 0.8 to 3.1 μm. We fit these spectra using both grids of forward models (Sonora Bobcat, Sonora Elf Owl, and ExoREM) and atmospheric retrievals (POSEIDON). We also constrain the composition of Ross 458 AB by fitting an archival SpeX spectrum with PHOENIX forward models. The forward model grids prefer an enhanced atmospheric metallicity for Ross 458 C relative to the host, but our retrievals return a metallicity consistent with the host within 1σ. Our results offer new insights into the formation history of Ross 458 C, as well as the efficacy of fitting forward model grids versus retrievals to derive atmospheric properties of directly imaged companions.

Keywords: Brown dwarfs, Planet formation, Exoplanet astronomy, Direct imaging, Exoplanet atmospheres, T dwarfs
Blue Supergiants and the Zero-point of the Tully─Fisher Relation: A Path to a New Independent Test of the Hubble Constant. Blue supergiant distances of nearby galaxies obtained with the flux-weighted gravity─luminosity relationship are used for a measurement of the zero-points of Tully─Fisher relationships at different photometric passbands. The Cousins I band and the infrared WISE bands W1 and W2 are investigated. The results are compared with previous work using Cepheid and tip of the red giant branch distances. No significant differences were encountered. This supports the large values of the Hubble constant greater than 73 km s−1 Mpc−1 found with the Tully─Fisher distance ladder work over the last decade. Applying blue supergiant distances on the I-band Tully─Fisher relation observations yields a Hubble constant H0 = 76.2 ± 6.2 km s−1 Mpc−1. The large uncertainty is caused by the still relatively small blue supergiant galaxy sample size but will be reduced in future work.

Keywords: Cosmology, Hubble constant, Galaxies, Distance indicators
Fast Radio Burst Cosmology with the Rotation Measure─Persistent Radio Source Luminosity Correlation. Fast radio bursts (FRBs) have emerged as a powerful tool for cosmological studies, particularly through the dispersion measure─redshift (DM─z) relation. This work proposes a novel calibration method for FRBs using the Yang─Li─Zhang (YLZ) empirical relation, which links the rotation measure of FRBs to the luminosity of their associated persistent radio sources (PRS). We demonstrate that this approach provides independent constraints on cosmological parameters, bypassing limitations inherent to the traditional DM─z method. Utilizing the current sample of four YLZ-calibrated FRBs, we derive a Hubble constant measurement of  H0=86.18−14.99+18.03kms−1Mpc−1  (68% CL). Monte Carlo simulations indicate that a future catalog of 400 FRB-PSR systems could reduce the relative uncertainty of H0 to 4.5%. Combining YLZ-calibrated FRBs with the DM─z sample reveals critical synergies: joint analysis of equalized samples (N = 100 for both methods) reduces the relative uncertainty of H0 to 2.9%, mainly because the incorporation of PRS observations substantially mitigates the degeneracy between the parameters such as intergalactic medium baryon mass fraction (fIGM) and other cosmological parameters inherent to the DM−z relation.

Keywords: Radio continuum emission, Radio bursts, Hubble constant, Radio transient sources
Micrometeoroid Impacts: Dual Pathways for Iron Reduction and Oxidation on Lunar and Asteroidal Surfaces. Nanophase metallic iron (npFe0) is a key indicator of space weathering on the lunar surface, primarily attributed to solar wind irradiation and micrometeoroid impacts. Recent discoveries of hematite (Fe2O3), a highly oxidized form of iron, in the lunar polar regions challenge the prevailing understanding of the Moon's reducing environment. This study, using ReaxFF molecular dynamics simulations of micrometeoroid impacts on fayalite (Fe2SiO4), investigates the atomistic mechanisms leading to both reduced and oxidized iron species. Our simulations reveal that the high-temperature and pressure conditions at the impact crater surface produce a reduced iron environment while providing a transient oxygen-rich environment in the expanding plume. Our findings bridge previously disparate observations, linking impact-driven npFe0 formation to the puzzling presence of oxidized iron phases on the Moon, explaining the observed strongly dichotomous distribution of hematite between the nearside and farside of the Moon. These findings highlight that micrometeoroid impacts, by simultaneously generating spatially distinct redox environments, provide a formation mechanism that reconciles the ubiquitous identification of nanophase metallic iron (npFe0) in returned lunar samples with Fe3+ signatures detected by remote sensing. This underscores the dynamic nature of space weathering processes. For a more nuanced understanding of regolith evolution, we should also consider the presence of different generations or types of npFe0, such as those formed from solar wind reduction versus impact disproportionation.

Keywords: Impact phenomena, Near-Earth objects, Lunar regolith, Molecular physics, Asteroid surfaces
Evaluating Habitability and Biosignature Detection on TOI-700 d: The Role of UV Environment and Atmospheric Pressure. M dwarfs have long been prime targets in the search for habitable exoplanets, owing to their abundance in the Galaxy and the relative ease of detecting Earth-sized worlds within their narrower habitable zones. Yet, these low-mass stars can emit high-energy radiation that may gradually erode planetary atmospheres, raising concerns about long-term habitability. TOI-700, a relatively quiescent M dwarf that hosts four known planets, stands out due to its Earth-sized TOI-700 d in the star's habitable zone. Here, we assess whether a habitable environment can be sustained on TOI-700 d by analyzing different UV flux levels and atmospheric pressures. We focus on two atmospheric scenarios, one analogous to the Archean Earth and another representing a modern Earth-like environment, using a 1D climate-photochemistry model. Our results indicate that all simulated cases can maintain temperatures compatible with liquid water on the surface. However, the dominant photochemical pathways differ substantially with UV levels: under low-UV conditions, haze formation in the Archean-like atmospheres provides the main UV shielding, whereas under intensified UV, ozone production in the modern Earth-like atmospheres can protect the surface from harmful doses. Interestingly, although haze can impede the detection of certain biosignatures, such as CH4, CO2 and O2, it also enhances the overall atmospheric signal by increasing scattering and transit depth, potentially aiding in revealing the presence of an atmosphere. These findings underscore the dual role of hazes as both a challenge for biosignature detection and a potential protection of surface habitability.

Keywords: Exoplanets, Transmission spectroscopy, Ultraviolet astronomy, Habitable planets, Exoplanet atmospheres
Evidence of Time-dependent Diffusive Shock Acceleration in the 2022 September 5 Solar Energetic Particle Event. On 2022 September 5, a large solar energetic particle (SEP) event was detected by Parker Solar Probe (PSP) and Solar Orbiter (SolO) at heliocentric distances of 0.07 and 0.71 au, respectively. PSP observed an unusual velocity dispersion signature: particles below ∼1 MeV exhibited a normal velocity dispersion, while higher-energy particles displayed an inverse velocity arrival (IVA) feature, with the most energetic particles arriving later than those at lower energies. The maximum energy increased from about 20─30 MeV upstream to over 60 MeV downstream of the shock. The arrival of SEPs at PSP was significantly delayed relative to the expected onset of the eruption. In contrast, SolO detected a typical large SEP event characterized by a regular velocity dispersion at all energies up to 100 MeV. To understand these features, we simulate particle acceleration and transport from the shock to the observers with our newly developed SEP model—Particle ARizona and MIchigan Solver on Advected Nodes. Our results reveal that the IVA and delayed particle onset detected by PSP originate from the time-dependent diffusive shock acceleration processes. After shock passage, PSP's magnetic connectivity gradually shifted due to its high velocity near perihelion, detecting high-energy SEPs streaming sunward. Conversely, SolO maintained a stable magnetic connection to the strong shock region where efficient acceleration was achieved. These results underscore the importance of spatial and temporal dependence in SEP acceleration at interplanetary shocks and provide new insights to understand SEP variations in the inner heliosphere.

Keywords: Solar energetic particles, Solar coronal mass ejection shocks, Interplanetary particle acceleration
On the Distance to the Black Hole X-Ray Binary Swift J1727.8─1613. We review the existing distance estimates to the black hole X-ray binary Swift J1727.8─1613, present new radio and near-UV spectra to update the distance constraints, and discuss the accuracies and caveats of the associated methodologies. We use line-of-sight H I absorption spectra captured using the MeerKAT radio telescope to estimate a maximum radial velocity with respect to the local standard of rest of 24.8 ± 2.8 km s−1 for Swift J1727.8−1613, which is significantly lower than that of a nearby extragalactic reference source. From this, we derive a near-kinematic distance of dnear = 3.6 ± 0.3 (stat) ± 2.3 (sys) kpc as a lower bound after accounting for additional uncertainties given its Galactic longitude and latitude, (l, b) ≍ (8.6°, 10.3°). Near-UV spectra from the Hubble Space Telescope's Space Telescope Imaging Spectrograph allows us to constrain the line-of-sight color excess to E(B ─ V) = 0.37 ± 0.01 (stat) ± 0.025 (sys). We then implement this in Monte Carlo simulations and present a distance to Swift J1727.8−1613 of  5.5−1.1+1.4  kpc, under the assumption that the donor star is an unevolved, main-sequence K4(±1)V star. This distance implies a natal kick velocity of 190 ± 30 km s−1 and therefore an asymmetrical supernova explosion within the Galactic disk as the expected birth mechanism. A lower distance is implied if the donor star has instead lost significant mass during the binary evolution. Hence, more accurate measurements of the binary inclination angle or donor star rotational broadening from future observations would help to better constrain the distance.

Keywords: Black hole physics, X-ray binary stars, Distance measure, Neutral hydrogen clouds, Interstellar reddening, Radio transient sources
Cloud Tides Can Induce the Fast Disruption of Star Clusters and Offer an Explanation for Gaia Strings. Young stars form in clusters within molecular clouds, but older stars are evenly distributed across the galactic disk, necessitating an explanation for cluster dissolution. We analytically study tidal forces from cold molecular clouds as a key mechanism for accelerated cluster disruption. Cloud tides, caused by the gravitational pull of the parent cloud along the radial direction, arise from the spatial gradient of gravitational acceleration and drive cluster disruption. This mechanism activates after gas expulsion and remains effective until the cloud is disrupted by stellar feedback or the cluster moves away. Cloud tides act on gas-deprived clusters, causing exponential expansion on a tidal timescale of  ttidal,ext=3/(8πGρmean) , where ρmean is the cloud's density at the cluster's location. With a duration of a few Myr, cloud tides can lead to a 10 times increase of the cluster size, producing bar-like elongated stellar aggregations resembling Gaia strings. These results establish cloud tides as a potentially important mechanism for star cluster disruption.

Keywords: Giant molecular clouds, Tidal disruption, Star clusters