Sazuna/UAT_keywords huggingface dataset:
Toward Characterizing Dark Matter Subhalo Perturbations in Stellar Streams with Graph Neural Networks. The phase space of stellar streams is proposed to detect dark substructure in the Milky Way through the perturbations created by passing subhalos—and thus is a powerful test of the cold dark matter paradigm and its alternatives. Using graph convolutional neural network (GCNN) data compression and simulation-based inference (SBI) on a simulated GD-1-like stream, we improve the constraint on the mass of a [108, 107, 106] M⊙ perturbing subhalo by factors of [11, 7, 3] with respect to the current state-of-the-art density power spectrum analysis. We find that the GCNN produces posteriors that are more accurate (better calibrated) than the power spectrum. We simulate the positions and velocities of stars in a GD-1-like stream and perturb the stream with subhalos of varying mass and velocity. Leveraging the feature encoding of the GCNN to compress the input phase space data, we then use SBI to estimate the joint posterior of the subhalo mass and velocity. We investigate how our results scale with the size of the GCNN, the coordinate system of the input, and the effect of incomplete observations. Our results suggest that a survey with 10× fewer stars (300 stars) with complete 6D phase space data performs about as well as a deeper survey (3000 stars) with only 3D data (photometry, spectroscopy). The stronger constraining power and more accurate posterior estimation motivate further development of GCNNs in combining future photometric, spectroscopic, and astrometric stream observations.

Keywords: Galaxy dark matter halos, Galaxy dynamics, Astronomical simulations, Neural networks
Asteroseismic Structure Inversions of Main-sequence Solar-like Oscillators with Convective Cores. Asteroseismic inferences of main-sequence solar-like oscillators often rely on best-fit models. However, these models cannot fully reproduce the observed mode frequencies, suggesting that the internal structure of the model does not fully match that of the star. Asteroseismic structure inversions provide a way to test the interior of our stellar models. Recently, structure inversion techniques were used to study 12 stars with radiative cores. In this work, we extend that analysis to 43 main-sequence stars with convective cores observed by Kepler to look for differences in the sound speed profiles in the inner 30% of the star by radius. For around half of our stars, the structure inversions show that our models reproduce the internal structure of the star, where the inversions are sensitive, within the observational uncertainties. For the stars where our inversions reveal significant differences, we find cases where our model sound speed is too high and cases where our model sound speed is too low. We use the star with the most significant differences to explore several changes to the physics of our model in an attempt to resolve the inferred differences. These changes include using a different overshoot prescription and including the effects of diffusion, gravitational settling, and radiative levitation. We find that the resulting changes to the model structure are too small to resolve the differences shown in our inversions.

Keywords: Stellar structures, Stellar evolutionary models, Stellar physics, Stellar oscillations, Asteroseismology
Quantifying Suppression of Solar Surface Magnetic Flux Advection with Increasing Field Strength. One of the main theories for heating of the solar corona is based on the idea that solar convection shuffles and tangles magnetic field lines to make many small-scale current sheets that, via reconnection, heat coronal loops. S. K. Tiwari et al. present evidence that, besides depending on loop length and other factors, the brightness of a coronal loop depends on the field strength in the loop's feet and the freedom of convection in the feet. While it is known that strong solar magnetic fields suppress convection, the decrease in the speed of horizontal advection of magnetic flux with increasing field strength has not been quantified before. We quantify that trend by analyzing 24 hr of Helioseismic Magnetic Imager-SHARP vector magnetograms of each of six sunspot-active regions and their surroundings. Using Fourier local correlation tracking, we estimate the horizontal advection speed of the magnetic flux at each pixel in which the vertical component of the magnetic field strength (Bz) is well above (≥150 G) noise level. We find that the average horizontal advection speed of magnetic flux steadily decreases as Bz increases, from 110 ± 3 m s‑1 for 150 G (in network and plage) to 10 ± 4 m s‑1 for 2500 G (in sunspot umbra). The trend is well fit by a fourth-degree polynomial. These results quantitatively confirm the expectation that magnetic flux advection is suppressed by increasing magnetic field strength. The presented quantitative relation should be useful for future MHD simulations of coronal heating.

Keywords: Solar magnetic fields, Solar coronal heating, Solar photosphere
Local Analogs of Primordial Galaxies: In Search of Intermediate-mass Black Holes with JWST NIRSpec. Local low-metallicity galaxies with signatures of possible accretion activity are ideal laboratories in which to search for the lowest-mass black holes and study their impact on the host galaxy. Here we present the first JWST NIRSpec IFS observations of SDSS J120122.30+021108.3, a nearby (z = 0.00354) extremely metal-poor dwarf galaxy with no optical signatures of accretion activity but identified by the Wide-field Infrared Survey Explorer to have red mid-infrared (MIR) colors consistent with active galactic nuclei (AGNs). We identify over 100 lines between ∼1.7 and 5.2 μm, an unresolved nuclear continuum source with an extremely steep spectral slope consistent with hot dust from an AGN (Fν ≈ ν‑1.5), and a plethora of H I, He I, and H2 lines, with no lines from heavier elements, CO or ice absorption features, or polycyclic aromatic hydrocarbons (PAHs). While the bright central unresolved source (≲5 pc) is suggestive of an AGN, there are no He II lines or coronal lines identified in the spectrum, and, importantly, there is no evidence that the radiation field is harder in the nuclear source compared with surrounding regions. The emission-line spectrum can be explained by a young (&lt;5 Myr) nuclear star cluster with stellar mass ∼3 × 104 M⊙, but the unresolved continuum source is more typical for a deeply embedded AGN powered by a black hole of minimum mass ∼1450 M⊙. These observations reveal that either a metal-poor stellar population can heat the dust to extremely high temperatures, a result that would have significant impact on the reliability of MIR color selection in AGN surveys and our understanding of the properties of the interstellar medium and young stars in metal-poor galaxies, or an accreting intermediate-mass black hole is deeply embedded and hidden even at near-infrared wavelengths.

Keywords: Andromeda Galaxy, Compact dwarf galaxies
The Robust Detection and Spatial Distribution of Acetaldehyde in Orion KL: Atacama Large Millimeter/submillimeter Array Observations and Chemical Modeling. Despite the organic molecule inventory detected in the Orion Kleinmann–Low Nebula (Orion KL), acetaldehyde (CH3CHO)—one of the most ubiquitous interstellar aldehydes—has not been firmly identified with millimeter-wave interferometry. We analyze extensive Atacama Large Millimeter/submillimeter Array archival data sets (142–355 GHz) to search for acetaldehyde, revealing two distinct acetaldehyde emission peaks and one component with more complex kinematic structures. One peak aligns with MF10/IRc2, where emissions of other O-bearing complex organic molecules are rarely reported, while the other is coincident with the ethanol peak in the southwest region of the hot core. The MF10/IRc2 detection suggests unique chemistry, possibly influenced by repeated heating events. In contrast, codetection with ethanol indicates an ice origin and suggests a potential chemical relationship between the two species. We determine acetaldehyde column densities and kinetic temperatures toward these two peaks under local thermodynamic equilibrium assumptions and compare its distribution with ethanol and other molecules that have an aldehyde (HCO) group, such as methyl formate, glycolaldehyde, and formic acid. Toward the ethanol peak, the observed abundance ratios between HCO-containing species are analyzed using a chemical model. The model suggests two key points: (1) the destruction of ethanol to form acetaldehyde in the ice may contribute to the observed correlation between the two species; and (2) a long cold-collapse timescale and a methyl formate binding energy similar to or lower than water are needed to explain the observations. The relative abundance ratios obtained from the model are highly sensitive to the assumed kinetic temperature, which accounts for the high spatial variability of the aldehyde ratios observed toward Orion KL.

Keywords: Interstellar molecules, Star forming regions, Complex organic molecules, Astrochemistry
Covariant Guiding Center Equations for Charged Particle Motions in General Relativistic Spacetimes. Low-density plasmas in curved spacetimes, such as those found in accretion flows around black holes, are challenging to model from first principles, owing to the large separation in scale between the characteristic scales of the microscopic processes and large mean free paths comparable to the system sizes. Kinetic approaches become necessary to capture the relevant physics but lack the dynamic range to model the global characteristics of the systems. In this paper, we develop new covariant guiding center equations of motion for charges in general relativistic spacetimes that are computationally tractable. We decompose the particle motion into a fast gyration, which we integrate analytically, and a slow drift of the guiding center, which can be solved numerically. We derive covariant conservation laws for the motions of the guiding centers and show, through several limiting cases, that the equations contain all known drift mechanisms. Finally, we present the general relativistic expressions for the various drift velocities in Schwarzschild spacetimes.

Keywords: Black holes, Plasma physics, Plasma astrophysics, General relativity, Astrophysical black holes
Quantum Machine Learning for Identifying Transient Events in X-Ray Light Curves. We investigate whether a novel method of quantum machine learning can identify anomalous events in X-ray light curves as transient events and apply it to detect such events from the XMM-Newton 4XMM-DR14 catalog. The architecture we adopt is a quantum version of long short-term memory (LSTM) where some fully connected layers are replaced with quantum circuits. LSTM, making predictions based on preceding data, allows for the identification of anomalies by comparing predicted and actual time-series data. The necessary training data are generated by simulating active-galactic-nucleus-like light curves as these events would be a significant population in the XMM-Newton catalog. Additional anomaly data used to assess trained quantum LSTM (QLSTM) models are produced by adding flare-like quasiperiodic eruptions to the training data. Comparing various aspects of the performances of the quantum and classical LSTM (CLSTM) models, we find that QLSTM models incorporating quantum superposition and entanglement slightly outperform the CLSTM model in expressive power, accuracy, and true-positive rate. The highest-performance QLSTM model is then used to identify transient events in 4XMM-DR14. Out of 40,154 light curves in the 0.2–12 keV band, we detect 113 light curves with anomalies, or transient event candidates. This number is ≈1.3 times that of anomalies detectable with the CLSTM model. By utilizing SIMBAD and four wide-field survey catalogs made by ROSAT, SkyMapper, Pan-STARRS, and the Wide-field Infrared Survey Explorer, no possible counterparts are found for 12 detected anomalies.

Keywords: X-ray astronomy, Astronomy data analysis, Active galactic nuclei, Time domain astronomy, Time series analysis
Quasars Can Signpost Supermassive Black Hole Binaries. Supermassive black holes (SMBHs) are found in the centers of massive galaxies, and galaxy mergers should eventually lead to SMBH mergers. Quasar activity has long been associated with galaxy mergers, so here we investigate if supermassive black hole binaries (SMBHBs) are preferentially found in quasars. Our multimessenger investigation folds together a gravitational-wave background signal from NANOGrav, a sample of periodic active galactic nucleus candidates from the Catalina Real-Time Transient Survey, and a quasar mass function, to estimate an upper limit on the fraction of quasars which could host an SMBHB. We find at 95% confidence that quasars are at most 5 times as likely to host an SMBHB as a random galaxy. Pulsar timing arrays may therefore be more likely to find SMBHBs by prioritizing quasars over a random selection of galaxies in their searches.

Keywords: Gravitational wave astronomy, Supermassive black holes, Gravitational waves, Quasars
Fast Transitions of X-Ray Variability in the Neutron Star Low-mass X-Ray Binary Cygnus X-2. We present a spectral-timing analysis of two NICER observations of the weakly magnetized neutron star low-mass X-ray binary Cygnus X-2. During these observations, we detect a rapid transition from a narrow 50 Hz horizontal-branch oscillation (HBO) to a broad 5 Hz normal-branch oscillation (NBO), accompanied by an increase in source flux and a decrease in spectral hardness. Thanks to the large effective area of NICER, we are able to conduct a detailed comparison of the spectra associated with different types of quasiperiodic oscillations (QPOs) on short timescales. By fitting the spectra with a model that includes a disk and Comptonization components plus two emission lines, we find that the parameters of the disk component do not change significantly during the transition. However, assuming a fixed electron temperature, the optical depth of the Comptonization component decreases significantly. This drop in optical depth may be attributed to the expansion of the boundary layer (BL) or spreading layer (SL). In addition, we find that the rms spectra for both the HBOs and NBOs are hard, suggesting that the BL or SL is driving the variability. We discuss the potential physical origin of the different types of QPOs.

Keywords: Low-mass x-ray binary stars, Neutron stars, Accretion, X-ray astronomy
Searching for Radio Pulses from Radio-quiet Gamma-Ray Pulsars with FAST. We present periodicity and single-pulse searches at 1250 MHz for 22 "radio-quiet" gamma-ray pulsars, conducted using the Five-hundred-meter Aperture Spherical Radio Telescope. For PSR J1813‑1246, we successfully detected pulsed signals with a spin period of 48.08 ms and a dispersion measure of 209.85 pc cm‑3, consistent with the spin period measured at gamma-ray wavelengths. The estimated flux density is approximately 9 μJy. For the remaining 21 sources, no radio emission was detected, with flux density upper limits of several μJy. The capability to detect pulsars with such low flux densities provides the opportunity to determine if and how these faint sources differ from much radio-brighter pulsars.

Keywords: Radio pulsars
Deep Neutral Hydrogen Observations of the Early-type Galaxy NGC 2768: Collided by a Newly Discovered Satellite Galaxy?. We present the results of a deep neutral hydrogen (H I) observation of the early-type galaxy NGC 2768 using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Leveraging the high sensitivity of FAST, we discover an extended gas envelope around NGC 2768. The total H I mass is measured to be 8.1 × 108 M⊙, representing a magnitude increase compared to previous Westerbork Synthesis Radio Telescope (WSRT) studies. A position-velocity (PV) diagram indicates the envelope mainly involves two components: an H I disk of NGC 2768 and a newly discovered satellite galaxy without detectable counterparts in currently deep optical surveys. The center of the gas disk is misaligned with the optical disk of NGC 2768, with more gas redshifted, indicating it has been disturbed. Our study indicates NGC 2768 is currently undergoing a transition from a spiral galaxy to an S0. Previous deep WSRT observations reveal two dense clumps (named "Clumps A" and "Clump B" throughout this paper) in the center of the envelope. We find Clump A corresponds to the densest part of the disk, while Clump B might be a newly discovered satellite galaxy that probably collided with NGC 2768 about 0.38 Gyr ago. We also find tidal interactions between Clump B and PGC 2599651, NGC 2768, and UGC 4808. Based on these new findings, we finally analyze the hierarchical accretion history of NGC 2768.

Keywords: Galaxy structure, Galaxy interactions
Heat-flux Instabilities of Regularized Kappa Distributed Strahl Electrons Resolved with ALPS. The fluid behavior of the solar wind is affected by the heat flux carried by the suprathermal electron populations, especially the electron strahl (or beam) that propagates along the magnetic field. In turn, the electron strahl cannot be stable, and in the absence of collisions, its properties are regulated mainly by self-generated instabilities. This paper approaches the description of these heat-flux instabilities in a novel manner using regularized Kappa distributions (RKDs) to characterize the electron strahl. RKDs conform to the velocity distributions with suprathermal tails observed in situ, and at the same time allow for consistent macromodeling, based on their singularity-free moments. In contrast, the complexity of RKD models makes the analytical kinetic formalism complicated and still inaccessible, and therefore, here heat-flux instabilities are resolved using the advanced solver ALPS. Two primary types of instabilities emerge depending on plasma conditions: the whistler and firehose heat-flux instabilities. The solver is successfully tested for the first time for such instabilities by comparison with previous results for standard distributions, such as Maxwellian and Kappa. Moreover, the new RKD results show that idealized Maxwellian models can overrate or underestimate the effects of these instabilities, and also show differences from those obtained for the standard Kappa, which, for instance, underestimate the firehose heat-flux growth rates.

Keywords: Space plasmas, Plasma physics, Plasma astrophysics, Solar physics, Alfven waves
Improving Optical Photo-z Constraints for Dusty Star-forming Galaxies Using Submillimeter-based Priors. Photometric redshifts (photo-z's) provide an efficient alternative to spectroscopic redshifts, enabling redshift estimation for large galaxy samples. However, traditional photo-z methods primarily rely on optical and near-infrared (OIR) photometry, which can struggle with dusty star-forming galaxies that are often faint in the OIR but bright at far-infrared (FIR) and millimeter wavelengths. We present a method for incorporating FIR-to-millimeter photometry as a prior within standard OIR-based photo-z frameworks, explicitly folding in the observed empirical relationship between total infrared luminosity and dust temperature. This approach is particularly suitable for wide-area surveys, such as those anticipated with the Euclid satellite or Rubin Observatory, where OIR photo-z's can be complemented with longer-wavelength data to help with the dustiest and highest star-forming galaxies. Applying this method to the Herschel Astrophysical Terahertz Large Area Survey (or H-ATLAS) catalog, which combines FIR photometry from Herschel-SPIRE with OIR observations, we achieve a threefold reduction in catastrophic outliers compared to traditional OIR-based photo-z techniques, demonstrating its utility for improving redshift estimates in FIR-bright galaxies.

Keywords: Cosmology, Far infrared astronomy, Photometry, Galaxy spectroscopy, Redshift surveys, Galaxies
Multiwavelength and Environmental Properties of Variability Selected Low-luminosity Active Galactic Nuclei. We present the multiwavelength and environmental properties of 37 variability-selected active galactic nuclei (AGNs), including 30 low-luminosity AGNs (LLAGNs), using a high cadence time-domain survey (All-Sky Automated Survey for SuperNovae) from a spectroscopic sample of 1218 nearby bright galaxies. We find that high-cadence time-domain surveys uniquely select LLAGNs that do not necessarily satisfy other AGN selection methods, such as X-ray, mid-IR, or BPT methods. In our sample, 3% of them pass the mid-infrared color based AGN selection, 18% pass the X-ray luminosity based AGN selection, and 60% pass the BPT selection. This result is supported by two other LLAGN samples from high-cadence time-domain surveys of the Transiting Exoplanet Survey Satellite and Palomar Transient Factory, suggesting that the variability selection method from well-sampled light curves can find AGNs that may not be discovered otherwise. These AGNs can have moderate to small variability amplitudes from the accretion disk, but many of them lack strong corona, emission lines from the central engine, or accretion power to dominate the mid-IR emission. The X-ray spectra of a subsample of bright sources are consistent with a power-law model. Upon inspecting the environments of our sample, we find that LLAGNs are more common in denser environments of galaxy clusters in contrast with the trend established in the literature for luminous AGNs at low redshifts, which is broadly consistent with our analysis result for luminous AGNs limited by a smaller sample size. This contrast in environmental properties between LLAGN and luminous AGNs suggests that LLAGNs may have different trigger mechanisms.

Keywords: Low-luminosity active galactic nuclei, Active galactic nuclei
Exploring the Future of Soft X-Ray Polarimetry: The Capabilities of the REDSoX Instrument for X-Ray Dim Isolated Neutron Star and Magnetar Studies. X-ray polarimetry offers a unique window into neutron star physics and can provide answers to questions that cannot otherwise be probed. The upcoming Rocket Experiment Demonstration of a Soft X-ray Polarimeter (REDSoX) sounding rocket mission will be the first experiment equipped with a detector able to explore polarized X-rays below 1 keV, observing in the 0.2–0.4 keV range. Although REDSoX will only be capable of short, one-off observations, it will crucially test the instrument performance. In this paper we investigate how a fully fledged orbital mission with a longer lifetime, based on an instrument design similar to REDSoX, will allow us to study thermal emission from X-ray dim isolated neutron stars (XDINSs) and magnetars, probing their magnetic fields and the physics of their outer surface layers, including vacuum effects and quantum electrodynamics (QED) mode conversion at the vacuum resonance. We discuss the potentially observable features for promising values of the star's surface temperature, magnetic field, and viewing geometry. Assuming emission from the whole surface, we find that, for a source with a magnetic field B = 5 × 1013 G and surface temperature T ≈ 107 K, the instrument can resolve a proton cyclotron absorption feature in the spectrum with high significance when collecting ≈25,000 counts across a single observation. Similarly, for a source with B = 1014 G and T ≈ 107 K, a switch in the dominant polarization mode, caused by mode conversion at the vacuum resonance, can be detected by collecting ≈25,000 counts, allowing for a long-sought observational test of the presence of QED effects. We then present two case studies for XDINS targets: RX J1856.5–3754 and RX J0720.4–3125.

Keywords: X-ray astronomy, Neutron stars, Polarimetry, Polarimeters, Magnetic fields, Stellar atmospheres