Sazuna/UAT_keywords huggingface dataset:
Can Fractal Dimension Distinguish between Grand-design and Flocculent Spiral Arms?. About two-thirds of disk galaxies host spiral arms, ranging from well-delineated grand-design spirals to fragmented flocculent spiral galaxies. We introduce fractal dimension DB as a nonparametric measure to distinguish between grand-designs and flocculents. We calculate the DB of 197 grand-designs and 322 flocculents from Sloan Digital Sky Survey (SDSS) DR18, using the samples of R. J. Buta et al. (2015) and S. Sarkar et al. (2023). Our calculated median values of DB are  1.29‑0.04+0.06  and  1.38‑0.06+0.05  for the grand-designs and flocculents, respectively. In addition, a Kolmogorov–Smirnov (K-S) test rejects the null hypothesis that these distributions are drawn from the same population. Finally, using a random forest model, we compare the effectiveness of DB in classifying spiral arm morphology with that of five other parameters: the total atomic hydrogen H I mass, MHI; the ratio of atomic hydrogen mass to blue luminosity, MHI/LB; concentration index, Ci; clumpiness, S; and arm contrast, C. Our results indicate that DB has the highest feature index (30.8%), followed by Ci (26.0%) and MHI (21.0%). In fact, C—the metric routinely used to distinguish between the spiral morphologies—has a feature importance of 8.3%. Further, DB for grand-designs is found to anticorrelate with the central velocity dispersion with a correlation coefficient of ‑0.3 and p ≪ 0.05. The high value of central velocity dispersion indicates a central Q-barrier, which favors the formation of grand-designs according to the density wave theory. Thus, the fractal dimension serves as a robust metric to distinguish between spiral morphologies and also links to the formation mechanism of the spiral features.

Keywords: Extragalactic astronomy
Three-component Phase Separation for Ultramassive White Dwarf Models. We investigate phase separation in oxygen-neon (O/Ne) ultramassive white dwarfs (UMWDs). Current stellar evolution codes, such as MESA, only account for 16O/20Ne separation and do not include other minor species. To improve this, we implement ternary phase diagrams into MESA. We construct UMWD models with O/Ne/sodium (Na) and O/Ne/magnesium (Mg) cores to test our implementation. We also assess the effect of including 22Ne in the current two-species framework. Our results show that incorporating additional components into the phase separation significantly alters the chemical evolution of UMWDs. Heavier elements preferentially enrich the solid core, enhancing mixing in the overlying liquid. We compute the buoyancy flux driven by compositional instabilities during crystallization. As in previous studies, we find two convective regimes: an early, fast overturning convection, lasting less than a million years, followed by inefficient (thermohaline) convection. The fast convective regime lasts up to 100 times longer with three-species separation compared to the standard 16O/20Ne case. We find that neutron-rich species can have a significant contribution to the buoyancy flux despite their small mass fraction (&lt;10%). We compute the amount of cooling delay induced by phase separation in UMWDs, and find that the three-species phase separation produces a delay of up to ∼10 times larger than the simplest case of fractionation, although still less than 1 Gyr. We predict that the change in the composition profile in the liquid region when three components are included should change the frequency of gravity modes that can propagate in the interior of pulsating UMWDs.

Keywords: White dwarf stars, Stellar evolutionary models, Stellar convective zones, Pulsating variable stars
Precise Parameters for Two LISA Sources. We present precise parameters for two compact double white dwarf (DWD) binaries, SDSS J232230.20+050942.0 (J2322+0509) and SDSS J063449.92+380352.2 (J0634+3803), with orbital periods of 20 and 26.5 minutes, respectively. These systems will serve as verification sources for the Laser Interferometer Space Antenna (LISA). To significantly improve the electromagnetic (EM) constraints on these two systems and the LISA detectability predictions, we conducted spectroscopic follow-up observations using Hubble Space Telescope/Space Telescope Imaging Spectrograph, Keck I/LRIS, and Keck II/Echellette Spectrograph and Imager. Our analysis significantly improves the temperature, surface gravity, and mass constraints for both primary and secondary components in J2322+0509, as well as dynamical properties such as radial velocities and orbital periods in both systems. For J2322+0509, we derive an updated inclination of i = 25 −3.0+4.5  deg, while for J0634+3803, we obtain i = 43 −5.6+7.0  deg. We assess the detectability of these sources using LDASOFT. Incorporating EM priors on inclination significantly enhances the gravitational-wave signal recovery, reducing uncertainties in amplitude by a factor of 2─4 and shortening the detection time by up to a few months. Our results underscore the importance of multimessenger observations in characterizing DWD binaries and maximizing LISA's early scientific capabilities.

Keywords: White dwarf stars, Compact binary stars, Gravitational wave sources, Detached binary stars, Compact objects
Semianalytic Modeling of Dark Matter Subhalo Encounters with Thin Stellar Streams: Statistical Predictions for GD-1-like Streams in Cold Dark Matter. Stellar streams from disrupted globular clusters are dynamically cold structures that are sensitive to perturbations from dark matter subhalos, allowing them in principle to trace the dark matter substructure in the Milky Way. We model, within the context of Λ cold dark matter, the likelihood of dark matter subhalos to produce a significant feature in a GD-1-like stream and analyze the properties of such subhalos. We generate many realizations of the subhalo population within a Milky Way mass host halo using the semianalytic code SATGEN, accounting for effects such as tidal stripping and dynamical friction. The subhalo distributions are combined with a GD-1-like stream model, and the impact of subhalos that pass close to the stream are modeled with GALA. We find that subhalos with masses in the range 2 × 106 M⊙–108 M⊙ at the time of the stream–subhalo encounter, corresponding to masses of about 2 × 107 M⊙–109 M⊙ at the time of infall, are the likeliest to produce gaps in a GD-1-like stream. We find that gaps occur on average ∼3 times per realization of the host system. These gaps have typical widths of ∼(5–27)° and fractional underdensities of ∼(10–30)%, with larger gaps being caused by heavier subhalos. The stream–subhalo encounters responsible for these have impact parameters (0.1–1.5) kpc and relative velocities ∼(200–410) km s‑1. We also investigate the effects of increasing the host-halo mass on the gap properties and formation rate.

Keywords: Milky Way dark matter halo, Dark matter distribution, Milky Way dynamics, Stellar streams
X-Ray Polarization Detection of the Pulsar Wind Nebula in G21.5–0.9 with IXPE. We present the X-ray polarization observation of G21.5‑0.9, a young Galactic supernova remnant (SNR), conducted with the Imaging X-ray Polarimetry Explorer (IXPE) in 2023 October, with a total livetime of approximately 837 ks. Using different analysis methods, such as a space-integrated study of the entire region of the pulsar wind nebula (PWN) and a space-resolved polarization map, we detect significant polarization from the PWN at the center of the SNR, with an average polarization degree of ∼10% oriented at ∼33° (north through east). No significant energy-dependent variation in polarization is observed across the IXPE band (2–8 keV). The polarization map, corrected for the effect of polarization leakage, reveals a consistent pattern in both degree and angle, with little change across the nebula. Our findings indicate the presence of a highly polarized central torus, suggesting low levels of turbulence at particle acceleration sites. Unlike Vela, but similar to the Crab Nebula, we observe substantial differences between radio and X-ray polarization maps. This suggests a clear separation in energy of the emitting particle populations and hints at an important, yet poorly understood, role of instabilities in the turbulence dynamics of PWNe.

Keywords: X-ray astronomy, Polarimetry, Pulsars, Pulsar wind nebulae
Linear Polarization in a Black Hole, 4U 1957+115 and Its X-Ray Spectral Analysis. We present a new spectropolarimetric method for the estimation of the inclination of X-ray binaries using the linear polarization (LP) value in black hole (BH) sources, based on the early paper by R. A. Sunyaev &amp; L. G. Titarchuk. The X-ray LP arises from multiple scattering of initially soft photons in a hot, optically thick Compton cloud (CC) using a flat geometry. R. A. Sunyaev &amp; L. G. Titarchuk showed that the LP degree P depends on the binary inclination i and remains independent of the photon energy. Moreover, P follows a characteristic angular distribution based on the CC optical depth τ0; in particular, for τ0 &gt; 10, the LP follows the S. Chandrasekhar distribution. In light of the vast number of recent IXPE spectropolarimetric observations of BHs, testing this approach in combination with spectral analysis of these sources by other missions is desirable. In particular, the BH source, 4U 1957+115, was observed with IXPE in the high/soft state for which a P of ∼ 2% was found. To apply the new method, in addition to knowing P for a given source, it is necessary to estimate the CC optical depth τ0 and then to calculate the best-fit photon index Γ and the plasma temperature kTe. We present the X-ray spectral analysis of 4U 1957+115 using data from IXPE, NuSTAR, NICER, RXTE, Swift, Suzaku, and ASCA. We show that the X-ray source spectra are well described by the Comptonization model with Γ varying from 1.5 to 3. We find a monotonic increase in Γ with the mass accretion rate,  Ṁ , and a final saturation of the index at Γ ∼ 3 for high  Ṁ . We determine a BH mass by the scaling method: M1957 = 4.8 ± 1.8M⊙, assuming a source distance of 22 kpc, using H 1743─322, 4U 1630─47, and GRS 1915+105 as reference sources.

Keywords: X-ray astronomy, Spectropolarimetry, High energy astrophysics, Stellar mass black holes, Stellar accretion disks
SIDM Concerto: Compilation and Data Release of Self-interacting Dark Matter Zoom-in Simulations. We present SIDM Concerto: 14 cosmological zoom-in simulations in cold dark matter (CDM) and self-interacting dark matter (SIDM) models based on the Symphony and Milky Way-est suites. SIDM Concerto includes one Large Magellanic Cloud─ (LMC-) mass system (host mass ∼1011 M⊙), two Milky Way (MW) analogs (∼1012 M⊙), two group-mass hosts (∼1013 M⊙), and one low-mass cluster (∼1014 M⊙). Each host contains ≍2 × 107 particles and is run in CDM and one or more strong, velocity-dependent SIDM models. Our analysis of SIDM (sub)halo populations over seven subhalo mass decades reveals that (1) the fraction of core-collapsed isolated halos and subhalos peaks at a maximum circular velocity corresponding to the transition of the SIDM cross section from a v−4 to v0 scaling; (2) SIDM subhalo mass functions are suppressed by ≍50% relative to CDM in LMC, MW, and group-mass hosts but are consistent with CDM in the low-mass cluster host; (3) subhalos' inner density profile slopes, which are more diverse in SIDM than in CDM, are sensitive to both the amplitude and shape of the SIDM cross section. Our simulations provide a benchmark for testing SIDM predictions with astrophysical observations of field and satellite galaxies, strong lensing systems, and stellar streams. Data products are publicly available at doi:10.5281/zenodo.14933624.

Keywords: Galaxy dark matter halos, Dark matter, N-body simulations
Results of 15 yr Pulsar Timing of PSR J0007+7303 with Fermi-LAT. The study of pulsar glitches provides a unique window into the internal structure and dynamic processes of neutron stars. PSR J0007+7303, a very bright gamma-ray pulsar, is the first pulsar discovered by the Fermi─Large Area Telescope (LAT) telescope. In this paper, we present the 15 yr of timing results of this pulsar using the Fermi-LAT data. We identified nine glitches, five of which are newly discovered. Among these new glitches, two are small glitches, occurring between the three previously reported ones, while the other three are large glitches. The glitches exhibit fractional frequency changes ranging from 21.5 × 10−9 to 1239 × 10−9, with intervals of approximately 1─2 yr between events. Uniquely, this pulsar shows no exponential recovery behavior following any glitch, setting it apart from most glitching pulsars. Furthermore, no significant changes were observed in the gamma-ray pulse profile, flux, or phase-averaged spectra before and after glitches, indicating the stability of the pulsar's emission properties despite internal changes. A parametric analysis of the glitches yielded a fractional moment of inertia of the crustal superfluid involved in glitches as 1.06%, which matches extremely well with previous statistical work if the nondissipative entrainment effect is not considered and strongly supports the internal origin of these glitches. These results highlight the distinct glitch behavior of PSR J0007+7303 and offer valuable insights into the crust─superfluid interaction in neutron stars. The physical origin of no exponential recovery is also discussed.

Keywords: Gamma-rays
Radiative Magnetohydrodynamics Simulation of Minidisks in Equal-mass Massive Black Hole Binaries. We are on the cusp of detecting gravitational waves (GWs) from individual massive black hole binaries (MBHBs) with the Laser Interferometer Space Antenna and pulsar timing arrays. These MBHBs may be surrounded by circumbinary disks and minidisks, the electromagnetic emission from which is essential for localizing the MBHBs on the sky. Here we present the first radiative magnetohydrodynamics (RMHD) minidisk simulation that directly solves the radiative transfer equation on discretized grid rays. The simulation examines one of the minidisks in an equal-mass 2 × 107 M⊙ MBHB separated by 100 gravitational radii. Minidisks simulated with and without radiative effects resemble each other qualitatively but differ in several key aspects. The RMHD minidisk is denser and geometrically thinner than the magnetohydrodynamics minidisk. Furthermore, the RMHD minidisk, with a nonaxisymmetric photosphere and temperature distribution, produces an anisotropic illumination pattern. As a result, the observed radiative flux of two RMHD minidisks orbiting each other varies at half the binary orbital period, a feature independent of relativistic boosting and lensing effects. Such periodic light curves, if identified in upcoming optical transient surveys, could reveal the existence of MBHBs on the way to merger, particularly if they are in a constant phase relation with detected GWs.

Keywords: Accretion, Supermassive black holes, Black hole physics, Radiative magnetohydrodynamics, Gravitation, Gravitational wave sources
Cosmography with the Double-source-plane Strong Gravitational Lens AGEL150745+052256. Strong gravitational lenses with two background sources at widely separated redshifts are a promising independent probe of cosmological parameters. We can use these systems, known as double-source-plane lenses (DSPLs), to measure the ratio (β) of angular-diameter distances of the sources, which is sensitive to the matter density (Ωm) and the equation-of-state parameter for dark-energy (w). However, DSPLs are rare and require high-resolution imaging and spectroscopy for detection, lens modeling, and measuring β. Here, we report only the second DSPL ever used to measure cosmological parameters. We model the DSPL AGEL150745+052256 from the ASTRO 3D Galaxy Evolution with Lenses (AGEL) survey using Hubble Space Telescope/Wide-Field Camera 3 imaging and Keck Cosmic Web Imager spectroscopy. The spectroscopic redshifts for the deflector and two sources in AGEL1507 are zdefl = 0.594, zS1 = 2.163, and zS2 = 2.591. We measure a stellar velocity dispersion of σobs = 109 ± 27 km s−1 for the nearer source (S1). Using σobs for the main deflector (from literature) and S1, we test the robustness of our DSPL model. We measure  β=0.953−0.010+0.008  for AGEL1507 and infer Ωm  =0.33−0.23+0.38  for ΛCDM cosmology. Combining AGEL1507 with the published model of the Jackpot lens improves the precision on Ωm (ΛCDM) and w (wCDM) by ∼10%. The inclusion of DSPLs significantly improves the constraints when combined with Planck's cosmic microwave background observations, enhancing the precision on w by 30%. This paper demonstrates the potential constraining power of DSPLs and their complementarity to other standard cosmological probes. Tighter future constraints from larger DSPL samples discovered from ongoing and forthcoming large-area sky surveys would provide insights into the nature of dark energy.

Keywords: Cosmological parameters, Strong gravitational lensing, Observational cosmology, Dark matter density, Baryonic dark matter, Gravitational lensing, Cosmological constant, Dark energy
Probing Binary Architectures of Lithium-rich Giants in GALAH with COSMIC and Stellar Models. Surface lithium is depleted when a star goes through the first dredge-up phase, yet 1% of red giants are found to be Li rich. The formation mechanism for these remains uncertain. We combine observational constraints from Galactic Archaeology with HERMES (GALAH) Li-rich giants, with the binary population synthesis software Compact Object Synthesis and Monte Carlo Investigation Code (COSMIC) to investigate the system properties of these objects assuming binary mass transfer. By evolving nine million binary systems, we find that binary histories most consistent with the observational constraints are mass transfer from an intermediate-mass asymptotic giant branch (AGB) donor to a main-sequence (MS) star now observed as a Li-rich red giant. In GALAH, 9% of MS stars have A(Li) = 2.5–3.2 dex making it plausible to create red giants with A(Li) = 1.5–2.2 dex via MS mass transfer, but they cannot explain the more enriched giants with A(Li) ≳ 2.2 dex. Nucleosynthetic yields from stellar models show that AGB stars with initial masses of 4.25–5 M⊙ and 8 M⊙ contain the most lithium in their ejecta. Intermediate-mass AGB stars comprise 29% of the COSMIC results, with present-day separations s = 3.3 ± 0.5 au and mass ratios q = 0.5–1.6. We achieve 95% agreement in mean enhancements in Ba and Y between the GALAH observations and stellar models of 6 and 8 M⊙ AGB stars, assuming a 1% mass transfer efficiency. We find a low mass transfer efficiency best reproduces the GALAH observations suggesting that the preferred mass transfer mechanism for Li enrichment is via wind Roche-lobe overflow. While we constrain the most plausible binary parameters assuming AGB mass transfer creates Li-rich giants, discrepancies in the nucleosynthesis comparisons and the small fraction of Li-enhanced MS stars suggests additional enrichment mechanisms are likely.

Keywords: Binary stars, Stellar evolutionary models, Asymptotic giant branch stars, Red giant stars, Chemically peculiar stars, Stellar evolution
A Search for z = 5 Hα and Hβ + [O III] Dual-line Emitting Galaxies in the JWST CEERS Field: Implications for the Active Galactic Nucleus Abundance. The James Webb Space Telescope (JWST) has enabled us to uncover faint galaxies and active galactic nuclei (AGNs) in the early Universe. Leveraging the filter combination used in the Cosmic Evolution Early Release Science Survey program, we perform an extensive photometric search of galaxies emitting strong Hβ + [O III] and Hα lines. The redshift range of the galaxies is limited to 5.03 ≤ z ≤ 5.26 by requiring photometric excess in NIRCam's F277W and F410M images. A total of 259 Hβ + [O III] and Hα dual-line emitters are found over the absolute UV magnitude −22 ≲ MUV ≲ −17, with a mean rest-frame equivalent width of 990 Å for Hβ + [O III] and 1050 Å for Hα. This population accounts for ∼40% of the Lyman-break galaxies at this redshift range. Intriguingly, there are 58 objects (22% of the whole sample) that exhibit compact morphology at the rest-UV or optical wavelength. Assuming that these compact dual-line emitters are dominated by AGNs, their bolometric luminosities are in the range of 2 × 1043 ≲ Lbol/(erg s−1) ≲ 3 × 1044. Their number density is 2 dex higher than the extrapolation from UV-selected luminous quasars, which is in good agreement with previous JWST studies of broad-line AGNs, requiring a ∼10% AGN duty cycle. Moreover, our dual-line emitter sample reaches the faint end of the Hα and [O III] luminosity functions down to ≲1042 erg s−1. Spectroscopic follow-up observations are planned in a JWST Cycle 3 program, in which we aim to confirm their nature, characterize their black hole activity, and construct their mass distribution at 106 ≲ MBH/M⊙ ≲ 108.

Keywords: Supermassive black holes, Galaxy formation, High-redshift galaxies, Quasars
Subparsec Acceleration and Collimation of NGC 4261's Twin Jets. We report the first robust evidence for a cospatial subparsec acceleration and collimation zone (ACZ) in the twin jets of the nearby low-luminosity active galactic nucleus NGC 4261. This result is derived from multifrequency Very Long Baseline Array imaging, combined with the frequency-dependent properties of the radio core (core shift and core size) and jet kinematics determined from the jet-to-counterjet brightness ratio. By applying multiple analysis methods and incorporating results from the literature, we identify a parabolic-to-conical structural transition in both the jet and counterjet, with the transition occurring at (1.23 ± 0.24) pc or (8.1 ± 1.6) × 103 Rs (Schwarzschild radii) for the jet and (0.97 ± 0.29) pc or (6.4 ± 1.9) × 103 Rs for the counterjet. We also derive the jet velocity field at distances of ∼(103–2 × 104) Rs. While local kinematic variations are present, the jet shows an overall acceleration to relativistic speeds from ∼103 to ∼8 × 103 Rs, with a maximum Lorentz factor of  Γmax≈2.6 . Beyond this region, the jet gradually decelerates to subrelativistic speeds. These findings support the existence of a subparsec-scale (≲1.5 pc) ACZ in NGC 4261, where the jet is accelerated via magnetic-to-kinetic energy conversion while being confined by external pressure. A brief comparison with M87 suggests that the ACZ in NGC 4261 may represent a scaled-down analog of that in M87. These results point toward a potential diversity in jet ACZ properties, emphasizing the importance of extending such studies to a broader AGN population to elucidate the physical mechanisms at play.

Keywords: Very long baseline interferometry, Low-luminosity active galactic nuclei, Relativistic jets, High angular resolution