Sazuna/UAT_keywords huggingface dataset:
Deep in the Fields of the Andromeda Halo: Discovery of the Pegasus VII Dwarf Galaxy in UNIONS. We present the newly discovered dwarf galaxy Pegasus VII (Peg VII), a member of the M31 subgroup which has been uncovered in the ri photometric catalogs from the Ultraviolet Near-Infrared Optical Northern Survey and confirmed with follow-up imaging from both the Canada─France─Hawaii Telescope and the Gemini-North Telescope. This system has an absolute V-band magnitude of −5.7 ± 0.2 mag and a physical half-light radius of 177  pc, which is characteristic of dynamically confirmed Milky Way satellite dwarf galaxies and about 5 times more extended than the most extended M31 globular clusters. Peg VII lies at a three-dimensional separation from M31 of 331  kpc, and a significant elongation (ϵ ∼ 0.5) toward the projected direction of M31 could be indicative of a past tidal interaction, but additional investigation into the orbit, star formation history, and whether any gas remains in the galaxy is needed to better understand the evolution of Peg VII.

Keywords: Local Group, Dwarf galaxies
The Host Galaxy (If Any) of the Little Red Dots. We investigate the host galaxy properties of eight little red dots (LRDs) selected from the JWST UNCOVER survey, applying a new technique (GalfitS) to simultaneously fit the morphology and spectral energy distribution using multiband NIRCam images covering ∼1–4 μm. We detect the host galaxy in only one LRD, MSAID38108 at z = 4.96, which has a stellar mass of  , an effective radius of   kpc, and a Sérsic index of  . No host emission centered on the central point source is found in the other seven LRDs. We derive stringent upper limits for the stellar mass of a hypothetical host galaxy by conducting realistic mock simulations that place high-redshift galaxy images under the LRDs. Based on the black hole masses estimated from the broad Hα emission line, the derived stellar mass limits are at least a factor of 10 lower than expected from the z ≈ 0 scaling relation between black hole mass and host galaxy stellar mass. Intriguingly, four of the LRDs (50% of the sample) show extended, off-centered emission, which is particularly prominent in the bluer bands. The asymmetric emission of two sources can be modeled as stellar emission, but the nature of the other two is unclear.

Keywords: AGN host galaxies, Early universe, Galaxy formation, Active galactic nuclei, High-redshift galaxies
Connection between Nonaxisymmetric Structures and Neutral Gas Distribution in Disk Galaxies. Nonaxisymmetric structures, such as bars and spiral arms, are known to concentrate molecular gas and star formation in galaxy centers, actively building up the pseudobulges. However, the direct link between the neutral (i.e., molecular and atomic) gas distribution and the exerted torque forces over a broader radial range of galactic disks still remains to be explored. In the present work, we investigate this link by carefully evaluating the torque force field using the 3.6 μm images for 17 The H I Nearby Galaxy Survey galaxies, and measuring neutral gas distribution on resolved atomic and molecular line maps. We find that galaxies with stronger torque forces show a more concentrated neutral gas distribution over the disk scale, defined as half the isophotal radius at  . The correlation holds regardless of whether the neutral gas fraction or the effective stellar mass surface density is controlled for. In addition, kiloparsec-scale neutral gas overdensities tend to be located close to the local maxima of torque forces. Most of these correlations involving the torque forces are comparatively stronger than those using the traditional Fourier amplitudes to quantify the nonaxisymmetric structures. These results are consistent with the scenario that nonaxisymmetric structures exert torque forces and trigger dissipative processes to transport gas inward, not only to build the pseudobulges but also to fuel the inner disk growth. In this regard, nonaxisymmetric structures inducing stronger torque forces appear to be more efficient in these processes.

Keywords: Galaxy bars, Disk galaxies, Galaxy structure, Spiral arms, Galaxy evolution, Interstellar medium
The Anomalous Acceleration of PSR J2043+1711: Long-period Orbital Companion or Stellar Flyby?. Based on the rate of change of its orbital period, PSR J2043+1711 has a substantial peculiar acceleration of 3.5 ± 0.8 mm s–1 yr–1, which deviates from the acceleration predicted by equilibrium Milky Way (MW) models at a 4σ level. The magnitude of the peculiar acceleration is too large to be explained by disequilibrium effects of the MW interacting with orbiting dwarf galaxies (∼1 mm s–1 yr–1), and too small to be caused by period variations due to the pulsar being a redback. We identify and examine two plausible causes for the anomalous acceleration: a stellar flyby, and a long-period orbital companion. We identify a main-sequence star in Gaia DR3 and Pan-STARRS DR2 with the correct mass, distance, and on-sky position to potentially explain the observed peculiar acceleration. However, the star and the pulsar system have substantially different proper motions, indicating that they are not gravitationally bound. However, it is possible that this is an unrelated star that just happens to be located near J2043+1711 along our line of sight (chance probability of 1.6%). Therefore, we also constrain possible orbital parameters for a circumbinary companion in a hierarchical triple system with J2043+1711; the changes in the spindown rate of the pulsar are consistent with an outer object that has an orbital period of 60 kyr, a companion mass of 0.3 M⊙ (indicative of a white dwarf or low-mass star), and a semimajor axis of 1900 au. Continued timing and/or future faint optical observations of J2043+1711 may eventually allow us to differentiate between these scenarios.

Keywords: Binary pulsars, Millisecond pulsars
A Linear Decomposition Method to Analyze and Study Pulsar Mode Changes. In this paper, we present the linear decomposition method (LDM), which we developed to detect and analyze pulsar profile variations and mode-changing behavior. We developed LDM utilizing the likelihood function approach assuming the Gaussian noise. The LDM projects pulse profiles onto significance-ordered orthonormal vector bases. We show that the method is similar to the principal component analysis, but the LDM can handle more general situations. We use a simulated data set and data from the Kunming 40 m radio telescope to demonstrate the application of the LDM. We found that the LDM successfully identified mode changes for well-known mode-changing PSR B0329+54 and found a continuous pulse profile evolution for PSR B0355+54. We also show that the LDM can be used to improve the timing precision for mode-changing PSR B0329+54.

Keywords: Radio pulsars
Polycyclic Aromatic Hydrocarbon and CO(2─1) Emission at 50─150 pc Scales in 70 Nearby Galaxies. Combining Atacama Large Millimeter/submillimeter Array CO(2─1) mapping and JWST near- and mid-infrared imaging, we characterize the relationship between CO(2─1) and polycyclic aromatic hydrocarbon (PAH) emission at ≍100 pc resolution in 70 nearby star-forming galaxies. Leveraging a new Cycle 2 JWST Treasury program targeting nearby galaxies, we expand the sample size by more than an order of magnitude compared to previous ≍100 pc resolution CO─PAH comparisons. In regions of galaxies where most of the gas is likely to be molecular, we find strong correlations between CO(2─1) and 3.3 μm, 7.7 μm, and 11.3 μm PAH emission, estimated from JWST's F335M, F770W, and F1130W filters. We derive power-law relations between CO(2─1) and PAH emission, with indices in the range 0.8─1.3, implying relatively weak variations in the observed CO-to-PAH ratios across our sample. We find that CO-to-PAH ratios and scaling relationships near H II regions are similar to those in diffuse sight lines. The main difference between the two types of regions is that sight lines near H II regions show higher intensities in all tracers. Galaxy centers show higher overall intensities and enhanced CO-to-PAH ratios compared to galaxy disks. Individual galaxies show 0.19 dex scatter in the normalization of CO at fixed IPAH, and this normalization anticorrelates with specific star formation rate and correlates with stellar mass. We provide a prescription that accounts for galaxy-to-galaxy variations, representing our best current empirical predictor to estimate CO(2─1) intensity from PAH emission, allowing one to take advantage of JWST's excellent sensitivity and resolution to trace cold gas.

Keywords: Dust nebulae, Disk galaxies, Dust continuum emission, Interstellar medium, CO line emission, Extragalactic astronomy
Jormungandr: A Large Substructure Circling the Milky Way Identified from Gaia DR3 Data. We report the discovery of a large substructure in the Milky Way passing through the solar neighborhood, detected in actions   calculated from Gaia DR3 data. We perform extensive tests to evaluate the selection effects present in the sample and conclude that they cannot produce an artifact with the same characteristics. This substructure, which we call Jormungandr, is orbiting the Milky Way with high LZ, higher eccentricity (median ∼0.50) and larger rotation velocity Vϕ compared to disk stars. It leaves obvious patterns in the integrals of motion and kinematics. The chemical abundances from the Apache Point Observatory Galactic Evolution Experiment DR17 for members of Jormungandr resemble those of the Galactic disk high-α sequence. It shows a significant spread in metallicity, as well as age, according to its color–magnitude diagram. Understanding its formation and nature requires further analysis and simulations.

Keywords: Stellar kinematics, Galaxy kinematics
Surveying the Giant H II Regions of the Milky Way with SOFIA. VII. Galactic Center Regions Sgr B1, Sgr B2, and Sgr C. This study examines the mid-infrared properties of Giant H II (GH II) regions in the Milky Way's Central Molecular Zone (CMZ)—Sgr B1, Sgr B2, and Sgr C—using SOFIA-FORCAST imaging at 25 and 37 μm. It compares these mid-infrared data with previous multiwavelength observations to explore their present star formation activity and global properties. The study identifies 77 massive young stellar object (MYSO) candidates in and around the three regions. Sgr B2 appears to host the youngest MYSOs and have much higher extinction than the other regions, containing several radio sources not detected in the mid-infrared even at 37 μm. Meanwhile, cm radio continuum regions of Sgr B1 shows remarkable correspondence to its mid-infrared emission. Sgr C has fewer confirmed MYSOs, and it seems to have a higher fraction of low-mass young stellar objects and contamination from more evolved interloper/foreground stars. Derived MYSO densities are consistent with GH II regions elsewhere in the Galactic plane, though the CMZ GH II regions appear to have less prolific present star formation overall. Unlike Sgr B2, the cm continuum emission in Sgr B1 and Sgr C GH II regions appears to be absent cold dust and molecular gas, suggesting environmental differences, possibly driven by turbulence and rapid dynamical changes near the Galactic center. Furthermore, unlike typical GH II regions, Sgr B1 and Sgr C are significantly ionized by evolved interloper stars, which likely did not form within these regions. In these ways, Sgr B1 and Sgr C deviate from classical GH II region behavior, thus potentially representing a new category of GH II region or challenging their classification as GH II regions.

Keywords: Star forming regions, Massive stars, Young star clusters, Infrared astronomy, Star formation, Infrared sources, Protostars, H II regions
Solar Energetic Particle Events with Extremely High <SUP>3</SUP>He Content Observed by Solar Orbiter. We performed a survey of 3He-rich events using observations from the Suprathermal Ion Spectrograph on the Solar Orbiter mission from 2020 to 2024. We identified 57 3He-rich events, each showing clear 3He enhancements above the background and 3He/4He abundance ratios greater than 1 in at least one energy channel in the range from 193.2 keV nucleon‑1 to 8.74 MeV nucleon‑1. The analysis of the events' abundance ratios shows characteristics of impulsive solar energetic particle events with 3He/4He ∼ 3.1 and Fe/O ∼ 1.3. We observe an energy dependence in the 3He/4He ratio, which increases with energy, while the Fe/O ratios are almost constant with energy. We also found that six events in our list have extremely high 3He content (e.g., 3He/C–Fe ratios in the range 25–62). These events show curved 3He and heavy nuclei spectra that roll over at higher energies and flatten toward low energy. Their spectral forms can be reasonably fit with simple exponentials with a 3He rollover energy in the range of a few hundred keV per nucleon and a C–Fe rollover energy ∼2–3 times lower. The differences in spectral rollover energy lead to a strong energy dependence of the ratio 3He/C–Fe, rising sharply with energy. We conclude that the features of these events with extremely high 3He content have a reasonable likelihood of depicting the initial acceleration process, which is driven by magnetic reconnection in flaring loops near the solar surface.

Keywords: Solar abundances, Solar physics, Solar particle emission
StreamSculptor: Hamiltonian Perturbation Theory for Stellar Streams in Flexible Potentials with Differentiable Simulations. Stellar streams are one of the most promising tracers of low-mass dark-matter subhalos. Existing frameworks for modeling stream perturbations rely on restrictive assumptions for the Milky Way potential (e.g., static, axisymmetric) or are computationally inefficient in generating many realizations of subhalo impacts. We present StreamSculptor, a GPU accelerated code that combines differentiable simulations and Hamiltonian perturbation theory to model the leading-order effect of dark-matter subhalos on stellar streams. Our model works in two stages: First, a base stream is generated in a Milky Way potential, including the effects of nonlinear time-dependent sources like the rotating Galactic bar and a massive satellite galaxy. Then, linear perturbation theory is applied to the base stream, allowing us to rapidly superimpose the effects of different subhalo impacts without having to carry out additional simulations. Subhalo masses and scale-radii can be rescaled as a postprocessing step. We demonstrate how this framework can be used to model subhalo impacts on stellar streams under realistic Milky Way conditions, specifically for an inner Galaxy stream like Palomar 5 and an outer Galaxy stream like Orphan–Chenab. We find that simultaneously modeling subhalo impacts and other time-dependent components of the Galactic gravitational potential is crucial for an unbiased inference of dark-matter substructure.

Keywords: Dark matter, Stellar streams, Milky Way Galaxy
A 100 Mpc<SUP>2</SUP> Structure Traced by Hyperluminous Galaxies around a Massive z = 2.85 Protocluster. We present wide-field mapping at 850 μm and 450 μm of the z = 2.85 protocluster in the HS 1549+19 field using the Submillimetre Common-User Bolometer Array 2. Spectroscopic follow-up of 18 bright sources selected at 850 μm, using the Northern Extended Millimeter Array and Atacama Large Millimeter/submillimeter Array, confirms that the majority lie near z ≃ 2.85 and are likely members of the structure. Interpreting the spectroscopic redshifts as distance measurements, we find that the submillimeter galaxies (SMGs) span 123 pMpc2 in the plane of the sky and demarcate a 3600 pMpc3 "pancake"-shaped structure in three dimensions. We find that the high star formation rates of these SMGs result in a total star formation rate of 20,000 M⊙ yr−1 from just the brightest galaxies in the protocluster. These rapidly star-forming SMGs can be interpreted as massive galaxies growing rapidly at large clustercentric distances before collapsing into a virialized structure. We find that the SMGs trace the Lyα surface density profile. Comparison with simulations suggests that HS 1549+19 could be building a structure comparable to the most massive clusters in the present-day Universe.

Keywords: High-redshift galaxies, Cosmic web, High-redshift galaxy clusters
HIP 8522: A Puzzling Young Solar Twin with the Lowest Detected Lithium Abundance. We present HIP 8522, a young solar twin with the lowest detected lithium abundance, potentially a field blue straggler or the result of episodic early accretion. Its stellar parameters (Teff = 5729 ± 7 K,   = 4.532 ± 0.016 dex, [Fe/H] = 0.005 ± 0.010 dex, and vt = 1.08 ± 0.02 km s‑1) and chemical composition were determined via spectroscopic equilibrium using high-resolution spectra (R = 60,000–165,000). The age of HIP 8522 was estimated to have an upper limit of &lt;1 Gyr through isochrone fitting and was further confirmed using chemical clocks. Spectral synthesis of the lithium line at ∼6707.8 Å yielded an upper lithium abundance limit of A(Li) &lt; 0.8 dex. This value is unusually low for solar twins of similar age, which typically have A(Li) values ranging from 2.0 to 3.3 dex, suggesting that ∼2 dex of lithium is missing. We investigate various scenarios, such as planet engulfment, substellar mergers, and extra mixing. However, two distinct hypotheses provide plausible explanations for the significant depletion of lithium: one suggests that HIP 8522 is a field blue straggler formed by the merger of a close binary, while the other proposes that HIP 8522 experienced early episodic accretion. The young solar twin HIP 8522 presents an exceptional opportunity to rigorously test stellar evolution models and gain crucial insights into the internal mixing mechanisms responsible for the significant destruction of lithium. *This research is based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan (NAOJ). We are honored and grateful for the opportunity of observing the Universe from the Maunakea, which has cultural, historical, and natural significance in Hawaii. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory (LCO), Chile.

Keywords: Accretion, Solar analogs, Fundamental parameters of stars, Stellar abundances, Spectroscopy, Blue straggler stars, Stellar atmospheres
Modeling the Solar Transition Region: Effects of Spatial Resolution on the Atmospheric Structure, Emission and Non-equilibrium Ionization. The solar transition region (TR) is a narrow interface between the chromosphere and corona, where emitted radiation contains critical information pertinent to coronal heating processes. We conducted two-dimensional radiation magnetohydrodynamics simulations using adaptive mesh refinement to spatially resolve the fine structure of the TR while simultaneously capturing the larger-scale dynamics originating from surface convection. The time evolution of ionization fractions for oxygen ions is computed alongside the simulations. A minimum grid size of 1.25 km is achieved in the TR, enabling adequate resolution of the upper TR (log10T ≳ 5), although the lower TR (log10T ≲ 5) remains under-resolved. Doppler shifts and nonthermal widths synthesized from TR lines exhibit convergence with grid sizes as coarse as 40 km, though some discrepancies persist between our results and observed TR line properties. A notable enhancement in emission from O VI lines, converging at a grid size of 2.5 km, shows an intensity 1.2 times that expected under ionization equilibrium, attributable to shock interactions with the TR. While model refinements are still required, our ability to resolve the TR offers critical insights into TR line characteristics arising from non-equilibrium ionization states, advancing our understanding of the coronal heating problem.

Keywords: Ultraviolet astronomy, Solar corona, Ionization, Solar transition region, Magnetohydrodynamical simulations
Using Lyα Absorption to Measure the Intensity and Variability of z ∼ 2.4 Ultraviolet Background Light. We present measurements of z ∼ 2.4 ultraviolet (UV) background light using Lyα absorption from galaxies at z ∼ 2–3 in the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) database. Thanks to the wide area of this survey, we also measure the variability of this light across the sky. The data suggest an asymmetric geometry where integrated UV light from background galaxies is absorbed by H I within the halo of a foreground galaxy, in a configuration similar to damped Lyα systems. Using stacking analyses of over 400,000 HETDEX LAE spectra, we argue that this background absorption is detectable in our data. We also argue that the absorption signal becomes negative due to HETDEX's sky-subtraction procedure. The amount that the absorption is oversubtracted is representative of the z ∼ 2.4 UV contribution to the overall extragalactic background light (EBL) at Lyα. Using this method, we determine an average intensity (in νJν units) of 12.9 ± 3.7 nW m‑2 sr‑1 at a median observed wavelength of 4134 Å, or a rest-frame UV background intensity of 508 ± 145 nW m‑2 sr‑1 at z ∼ 2.4. We find that this flux varies significantly depending on the density of galaxies in the field of observation. Our estimates are consistent with direct measurements of the overall EBL.

Keywords: Lyman-alpha galaxies, Diffuse radiation, Damped Lyman-alpha systems, Galaxies
Constraints on the X-Ray and Very-high-energy Gamma-Ray Flux from Supernova Remnant W44. Observations of GeV gamma-ray emission from the well-studied mixed-morphology supernova remnant (SNR) W44 by Fermi-Large Area Telescope and AGILE imply that it is a site of significant cosmic-ray acceleration. The spectral energy distribution (SED) derived from the GeV data suggests that the gamma-ray emission likely originates from the decay of neutral pions generated by cosmic-ray interactions. It is essential to measure the SED of W44 in the X-ray and very-high-energy (VHE) gamma-ray bands to verify the hadronic origin of the emission and to gauge the potential contributions from leptonic emission. We report an upper limit of the nonthermal X-ray flux from W44 of 5 × 10‑13 erg cm‑2 s‑1 in the 0.5–8.0 keV band based on ∼300 ks of XMM-Newton observations. The X-ray upper limit is consistent with previously estimated hadronic models, but in tension with the leptonic models. We estimate the VHE flux upper limit of ∼1.2 × 10‑12 erg s‑1 cm‑2 in the 0.5–5.0 TeV range from W44 using data from the Very Energetic Radiation Imaging Telescope Array System. Our nondetection of W44 at VHE wavelengths is in agreement with observations from other imaging atmospheric Cherenkov telescopes and is perhaps consistent with the evolutionary stage of the SNR.

Keywords: Supernova remnants, Gamma-ray astronomy, High energy astrophysics
A Spiral Structure in the Inner Oort Cloud. As the Galactic tide acts to decouple bodies from the scattered disk it creates a spiral structure in physical space that is roughly 15,000 au in length. The spiral is long-lived and persists in the inner Oort cloud to the present time. Here we discuss dynamics underlying the Oort spiral and (feeble) prospects for its observational detection.

Keywords: Oort cloud, Trans-Neptunian objects