Sazuna/UAT_keywords huggingface dataset:
Star Clusters in the Near-ultraviolet-optical-near-infrared: Spectral Energy Distribution Modeling with Direct Markers of Gas and Dust Emission. The large number of star clusters in nearby galaxies permits us to statistically test the predictions of stellar, dust, and gas models. Using Hubble Space Telescope (HST) broadband plus Hα imaging combined with JWST near-infrared imaging, we use a total of 10 filters spanning near-ultraviolet through near-infrared wavelengths to model key physical parameters, including age, mass, and reddening, of 6130 star clusters in 16 nearby spiral galaxies from the Physics at High Angular resolution in Nearby GalaxieS sample, focusing on their ages, masses, and reddenings. We find that HST/Hα and JWST/NIRCam 2─3.6 μm photometry significantly improves our ability to disentangle the age─reddening degeneracy between young, gas- and dust-rich clusters and older, dustless clusters. The near-infrared data provide strong constraints on hot continuum dust and small polycyclic aromatic hydrocarbon emission for populations where gas and dust are present. These hot dust constraints demonstrate that Bruzual &amp; Charlot stellar population models do not align with the observed near-ultraviolet-optical-near-infrared spectral energy distributions of star clusters in the first 10 Myr. We note that for old and low-metallicity globular clusters, the inclusion of narrowband Hα and/or broadband near-infrared data does not improve the determination of age and reddening parameters, due to the lack of stars capable of heating dust in the near-infrared regime.

Keywords: Star forming regions, Spectral energy distribution, Spiral galaxies, Star clusters
A Data-constrained Magnetohydrodynamic Simulation of Successive X-class Flares in Solar Active Region 13842. II. Dynamics of the Solar Eruption Associated with the X9.0 Solar Flare. Active region NOAA 13842 produced two successive solar flares: an X7.1-class flare on 2024 October 1, and an X9.0-class flare on 2024 October 3. This study continues our previous simulation work that successfully reproduced the X7.1-class solar flare. In this study, we performed a data-constrained magnetohydrodynamic simulation using the nonlinear force-free field (NLFFF) as the initial condition to investigate the X9.0-class solar flare. The NLFFF showed the sheared field lines, resulting in the tether-cutting reconnection, the magnetic flux ropes, and eventually led to eruption. The magnetic reconnection during the pre-eruption phase plays a critical role in accelerating the subsequent eruption, which is driven by torus instability and magnetic reconnection. Furthermore, our simulation results are consistent with several observational features associated with the X9.0 flare. This simulation could reproduce diverse phenomena associated with the X9.0 flare, including the tether-cutting reconnection, the flare ribbons and the postflare loops, the transverse field enhancement, and the remote brightening away from the flare ribbons. However, the initial trigger, magnetic flux emergence, was inferred from observations rather than explicitly modeled, and future comprehensive simulations should incorporate this mechanism directly.

Keywords: Solar active region magnetic fields, Magnetohydrodynamics, Solar flares, Magnetohydrodynamical simulations
The Averaged Broadband Spectral Energy Distribution Study of Fermi Bright BL Lac Objects. The physics-determined broadband spectral energy distributions (SEDs) of blazars have been widely used to study their properties during their flaring/outburst states, while the nonflaring state takes up most of their lifetime and the general property of blazars has been barely discussed. In this work, for the first time, we used the archival data and employed the physics-determined SED processing method to form approximately average-state SEDs for 513 Fermi bright BL Lacs. In general, we found that the magnetic field (B) is weaker than those obtained for the flaring/outburst state by nearly 1 order of magnitude, and the dissipation region size (R) is larger than those obtained for the flaring/outburst state, suggesting that the dissipation region could be more extended and less magnetized. A correlation between the synchrotron self-Compton peak frequency ( logνssc ) and the synchrotron peak frequency ( logνsy ) suggests that the inverse Compton scattering of higher-synchrotron-peaked BL Lacs suffers a significant Klein─Nishina (KN) suppression; we quantified the condition of KN suppression by determining the critical synchrotron peak frequency ( νsyc ) and found 359 out of 513 sources in our sample suffer KN suppression. Furthermore, our analysis of the relationship between synchrotron curvature (1/b sy) and  logνsy  indicates that the energy-dependent probability acceleration mechanism may dominate the particle acceleration in BL Lac jets.

Keywords: Blazars, Jets, BL Lacertae objects, Spectral energy distribution
A Magnetic Field Detection in the Massive O-type Bright Giant 63 Oph. Surface magnetic fields are detected in less than 10% of the massive O-type star population and even less frequently among "old" massive stars approaching the terminal-age main sequence (TAMS). It is unclear to what extent the rarity of magnetic detections in massive stars near the TAMS is due to magnetic field decay or observational biases. We report the detection of a weak surface magnetic field in the O-type giant 63 Oph (Teff = 35.0 ± 0.3 kK,  logg=3.51±0.03 ) from new ESPaDOnS circularly polarized spectra. The mean longitudinal field strength associated with the magnetic detection is &lt;Bz&gt; = 84 ± 14 G, which we use to set a lower limit on the dipolar field strength of Bp ≥ 300 ± 50 G. We report Balmer line-core equivalent widths (EWs) and radial velocity measurements from the analysis of spectra primarily obtained by the IACOB project with the FEROS, FIES, and HERMES spectrographs. We identify a dominant period of ∼19.8 days in the EWs, which we attribute to the effects of a rotating magnetosphere under the oblique rotator model. We do not identify any coherent signals in a time series analysis of archival Hipparcos, ASAS-SN, and K2 photometry. Our findings show that 63 Oph may be a rare link between strongly magnetic massive stars detected on or near the zero-age main sequence and weakly magnetic O-type supergiants. Additional observations are needed to fully constrain 63 Oph's magnetic field geometry and magnetospheric properties.

Keywords: Magnetic stars, Spectropolarimetry, Massive stars, Stellar magnetic fields, O giant stars
Polarization Signatures of Quasiperiodic Oscillations in Simulated Tilted, Truncated Disks. We utilize the Monte Carlo radiation transport code, Pandurata, to create images, spectra, polarization maps, and light curves from a set of general relativistic magnetohydrodynamic simulations of tilted, truncated, black hole accretion disks. Truncation can have spectral and polarization signatures all its own, tilt introduces both inclination and azimuthal dependencies into the spectra and polarization, and precession and oscillations of the tilted accretion flow inside the truncation radius introduce time dependencies or periodicity to all of this. We use the ray-traced results from our simulations to evaluate the feasibility of measuring these effects, particularly in the context of current and future X-ray polarization observatories. Such detections could greatly improve our understanding of the geometry of accretion disks and coronae in the hard state, the physics of quasiperiodic oscillations, and how system properties evolve as sources approach the hard-to-soft state transition.

Keywords: Accretion, Starlight polarization, Rotating black holes, Low-mass x-ray binary stars, Relativistic disks
Dynamics of Low-mass Black Hole Seeds in the BRAHMA Simulations Using Subgrid Dynamical Friction: Impact on Merger-driven Black Hole Growth in the High-redshift Universe. We analyze the dynamics of low-mass black hole (BH) seeds in the high-redshift (z ≳ 5) Universe using a suite of [4.5 Mpc]3 and [9 Mpc]3 BRAHMA cosmological hydrodynamic simulations. The simulations form seeds with mass Mseed = 2.2 × 103 M⊙ in halos that exceed critical thresholds of dense and metal-poor gas mass (5–150Mseed) and the halo mass (1000–10,000Mseed). While the initial BRAHMA boxes pinned the BHs to the halo centers, here we implement a subgrid dynamical friction (DF) model. We also compare simulations where the BH is allowed to wander without the added DF. We investigate the spatial and velocity offsets of BHs in their host subhalos, as well as BH merger rates. We find that subgrid DF is crucial to ensure that a significant fraction of BHs effectively sink to halo centers by z ∼ 5, thereby enabling them to get gravitationally bound and merge with other BHs at separations close to the spatial resolution (∼0.2–0.4 kpc) of the simulation. For the BHs that merge, the associated merger timescales lag between ∼100 and 1000 Myr after their host halos merge. Compared to predictions using BH repositioning, the overall z ≳ 5 BH merger rates under subgrid DF decrease by a factor of ∼4–10. Under subgrid DF, the different seed models predict merger rates between ∼100 and 1000 events per year at z ≳ 5. These mergers dominate early BH growth, assembling BHs up to ∼104–105 M⊙ by z ∼ 5, wherein ≲2% of their mass is assembled via gas accretion. Our results highlight the promise for constraining seeding mechanisms using gravitational waves from future facilities such as the Laser Interferometer Space Antenna.

Keywords: Supermassive black holes, Galaxy formation, Hydrodynamical simulations, Active galactic nuclei, Gravitational waves, Dynamical friction
TeV Afterglows of Gamma-Ray Bursts: Theoretical Analysis and Prospects for Future Observations. Recent detections of gamma-ray bursts (GRBs) at TeV energies opened new prospects for investigating radiative environments and particle acceleration mechanisms under extreme conditions. In this paper, we study the afterglows of these GRBs—namely GRB 180720B, GRB 190114C, GRB 190829A, GRB 201216C, and GRB 221009A—modeling their synchrotron and inverse Compton emission within the framework of an optimized relativistic fireball model. We constrain the model parameters and their temporal evolution by applying our theoretical model to the high-energy emission in the X-ray and GeV─TeV energy bands observed at intermediate and late times. Our results reveal interesting differences among the TeV-detected GRBs, potentially reflecting a variety of underlying physical processes that lead to different maximum energies  Emax=γmaxmec2  of the accelerated particles responsible for the GRB high-energy emission. We indeed obtain different behaviors of the late TeV afterglows that ultimately depend on  γmax . We discuss how late afterglow observations—on timescales of hours and days—of X-ray and GeV─TeV emissions are crucial for providing diagnostics of the physical processes behind GRBs, and we emphasize the theoretical expectations for future TeV observations.

Keywords: Gamma-ray astronomy, Gamma-ray bursts
Caught in the Act: Detections of Recoiling Supermassive Black Holes from Simulations. We study the detectability of supermassive black holes (SMBHs) with masses of M∙ ≳ 109M⊙ displaced by gravitational wave recoil kicks (vkick = 0─2000 km s−1) in simulations of merging massive (M⋆ &gt; 1011M⊙) early-type galaxies. The used KETJU code combines the GADGET-4 fast multiple gravity solver with accurate regularized integration and post-Newtonian corrections (up to PN3.5) around SMBHs. The ejected SMBHs carry clusters of bound stellar material (black hole recoil clusters, BRCs) with masses in the range of 106 ≲ MBRC ≲ 107M⊙ and sizes of several 10 pc. For recoil velocities up to 60% of the galaxy escape velocity, the BRCs are detectable in mock photometric images at a Euclid-like resolution up to redshift z ∼ 1.0. By Monte Carlo sampling the observability for different recoil directions and magnitudes, we predict that in ∼20% of instances the BRCs are photometrically detectable, most likely for kicks with SMBH apocentres less than the galaxy effective radius. BRCs occupy distinct regions in the stellar mass/velocity dispersion versus size relations of known star clusters and galaxies. An enhanced velocity dispersion in excess of σ ∼ 600 km s−1 coinciding with the SMBH position provides the best evidence for an SMBH-hosting stellar system, effectively distinguishing BRCs from other faint stellar systems. BRCs are promising candidates to observe the aftermath of the yet-undetected mergers of the most massive SMBHs and we estimate that up to 8000 BRCs might be observable below z ≲ 0.6 with large-scale photometric surveys such as Euclid and upcoming high-resolution imaging and spectroscopy with the Extremely Large Telescope.

Keywords: Supermassive black holes, Galaxy mergers, Astronomical simulations
Euclid Quick Data Release (Q1)—Spectroscopic Search, Classification, and Analysis of Ultracool Dwarfs in the Deep Fields. The Near-Infrared Spectrometer and Photometer on board the Euclid space mission has obtained near-infrared (NIR) slitless spectra of millions of objects, including hundreds of ultracool dwarfs (UCDs). Euclid observations retrieve images and spectra simultaneously. This observing mode marks a new era in the discovery of new objects, such as L- and T-type dwarfs, which can be found from direct identification through the H2O and CH4 absorption bands. NISP spectral resolution (R ∼ 450) is enough to classify the objects by the spectral type using known standard templates. Q1 provided more than 4 million NIR spectra in one visit to the Euclid Deep Fields. The large amount of spectra released in these fields allowed us to (a) confirm the UCD nature of almost half of the photometric candidates compiled by J. Y. Zhang et al.; (b) discover at least 11 new late L- and T-type dwarfs by a specific spectral index search in Q1 data; and (c) spectroscopically confirm 100 more candidates from a new photometric selection conducted by M. Žerjal et al. We present a preliminary list of Euclid UCD templates built by the combination of the best spectra from all these searches. We include the first spectral analysis of confirmed UCDs from Q1 data; spectral classifications; determination of effective temperatures; H2O, CH4, and NH3 spectral indices; and measurements of the K I absorption doublet. This paper is a first step in the study of Euclid UCDs and will be improved with each subsequent data release.

Keywords: Surveys, Late-type dwarf stars, Brown dwarfs, T dwarfs
Unveiling the Origin of Fast Radio Bursts by Modeling the Stellar Mass and Star Formation Distributions of Their Host Galaxies. Diverse formation channels have been proposed to explain the emergence of fast radio bursts (FRBs), yet their origin remains elusive. With improved localization precision, roughly 90 FRBs are now associated with host galaxies. Spectral energy distribution fitting to the host galaxy photometry reveals their stellar masses (M⋆) and star formation rates (SFRs), enabling discrimination between various formation channels. We conduct an extensive comparison of the stellar mass, SFR, and redshift distributions of 51 FRB hosts and mock generated galaxy samples to test whether FRBs trace SFR or M⋆. We incorporate a mass-to-light ratio ( (M⋆/Lr)obs ) prescription to address optical selection biases. In line with K. Sharma et al., we provide evidence in favor of FRB progenitors tracking SFR rather than stellar mass. We show that the shape of the assumed  (M⋆/Lr)obs  distribution affects the predictions, bringing the low-mass end of the stellar mass distribution closer to the data when accounting for the  SFR─(M⋆/Lr)obs  correlation. The K-correction effect in the r band is minimal for galaxies at z ≲ 0.7. In the model in which FRBs trace SFR, up to ∼6% of a flux-limited FRB host sample can reside below the star-forming main sequence. Finally, we examine a hybrid model in which a fraction of FRBs tracks stellar mass rather than SFR. This fraction can be as large as ∼40%−50%, suggesting that multiple formation channels are still consistent with observations. The toolkit developed in this work, GALFRB (https://github.com/loudasnick/GALFRB; N. Loudas et al.), is publicly available, offering a straightforward way to generate mock galaxy samples suitable for direct comparisons with future FRB host galaxy data.

Keywords: Radio bursts, Galaxies, Radio transient sources
Resolved Stellar and Nebular Kinematics of a Star-forming Galaxy at z ∼ 2. The kinematics of star-forming galaxy populations at high redshifts are integral to our understanding of disk properties, merger rates, and other defining characteristics. Nebular gas emission is a common tracer of galaxies' gravitational potential and angular momenta, but is sensitive to nongravitational forces as well as galactic outflows, and thus might not accurately trace the host galaxy dynamics. We present kinematic maps of young stars from rest-ultraviolet photospheric absorption in the star-forming galaxy CASSOWARY 13 (a.k.a. SDSS J1237+5533) at z = 1.87 using the Keck Cosmic Web Imager, alongside nebular emission measurements from the same observations. Gravitational lensing magnification of the galaxy enables good spatial sampling of multiple independent lensed images. We find close agreement between the stellar and nebular velocity fields. We measure a mean local velocity dispersion of σ = 64 ± 12 km s−1 for the young stars, consistent with that of the H II regions traced by nebular C III] emission (52 ± 9 km s−1). The ∼20 km s−1 average difference in line-of-sight velocity is much smaller than the local velocity width and the velocity gradient (≳100 km s−1). We find no evidence of asymmetric drift nor evidence that outflows bias the nebular kinematics, and thus we conclude that nebular emission appears to be a reasonable dynamical tracer of young stars in the galaxy. These results support the picture of star formation in thick disks with high velocity dispersion at z ∼ 2, and they represent an important step toward establishing robust kinematics of early galaxies using collisionless tracers.

Keywords: Galaxy formation, High-redshift galaxies, Galaxy evolution, Strong gravitational lensing
CIBER Fourth Flight Fluctuation Analysis: Pseudopower Spectrum Formalism, Improved Source Masking, and Validation on Mocks. Precise, unbiased measurements of extragalactic background anisotropies require careful treatment of systematic effects in fluctuation-based, broadband intensity mapping measurements. In this paper, we detail improvements in methodology for the Cosmic Infrared Background Experiment (CIBER), concentrating on flat field errors and source masking errors. In order to bypass the use of field differences, which mitigate flat field errors but reduce sensitivity, we characterize and correct for the flat field on pseudopower spectra, which includes both additive and multiplicative biases. To more effectively mask point sources at 1.1 and 1.8 μm, we develop a technique for predicting masking catalogs that utilizes optical and near-infrared photometry through random forest regression. This allows us to mask over 2 Vega mag deeper than the completeness limits of Two Micron All Sky Survey alone, with errors in the shot noise power remaining below &lt;10% at all masking depths considered. Through detailed simulations of CIBER observations, we validate our formalism and demonstrate unbiased recovery of the sky fluctuations on realistic mocks. We demonstrate that residual flat field errors comprise &lt;20% of the final CIBER power spectrum uncertainty with this methodology.

Keywords: Large-scale structure of the universe, Diffuse radiation, Galaxy evolution, Cosmic background radiation, Near infrared astronomy
Helicity Fluxes and Hemispheric Helicity Rule of Active Regions Emerging from the Convection Zone Dynamo. Using a 3D nonlinear mean field solar dynamo model, we investigate the magnetic helicity flux and magnetic twist, as well as tilt parameters of bipolar magnetic regions (BMRs) emerging from the solar convection zone owing to the magnetic buoyancy instability. The twist and tilt of the BMR magnetic field are modeled as a result of an effective electromotive force along the rising part of the toroidal magnetic field. This force generates the poloidal field that tilts the whole magnetic configuration. We find that variations of BMR's twist and tilt determine the magnitude and the sign of the magnetic helicity flux on the solar surface. The model shows that the helicity flux associated with the BMR's tilt/twist is the dominant contribution to the BMR helicity at the beginning of the BMR's evolution, while the effect of differential rotation is the main source of the helicity flux at the final stage of the BMR's evolution. We discuss the implications of these effects on the basic properties and variations of the hemispheric helicity rule of active regions on the solar surface.

Keywords: Solar cycle, Magnetic fields
Variability in Black Hole Accretion: Dependence on Rotational and Magnetic Energy Balance. Most general-relativistic magnetohydrodynamic simulations of black hole (BH) hot accretion flows are initialized with small rotating tori and produce stable jets with only small fluctuations. However, recent studies using larger-scale Bondi-like initial conditions have reported intermittent jet activity and loss of coherent rotation. To investigate these differences, we modify the standard torus setup across four BH spins: a* = 0, 0.5, 0.9, ‑0.9. First, we increase the torus size significantly (pressure maximum at 500 gravitational radii), allowing long simulations (2.8 × 105 gravitational times) without gas depletion. These runs reproduce the weak variability seen in smaller tori, indicating that a larger dynamic range alone does not cause strong fluctuations. We observe moderate suppression of the accretion rate by factors of ∼1.6 and 2.5 for BH spins a* = 0.5 and 0.9, respectively, compared to a* = 0. Also, the density profile scales as ρ(r) ∝ r‑1.1 for prograde BHs. Next, we considerably strengthen the initial magnetic field in the large torus by setting the plasma-β ≈ 1. This induces strong variability in the evolution. The jet efficiency in the a* = 0.9 model, for instance, now varies by over 3 orders of magnitude, and the gas rotation reverses directions. Combining these results with prior studies, we propose that a key parameter is the ratio  R  between the rotational and magnetic energies in the initial state. Strong variability appears later in models with larger values of  R . The implication is that all simulations, and by extension all hot accretion flows in nature, will ultimately develop intermittent jets if evolved long enough.

Keywords: Accretion, Relativistic jets, Black holes, Magnetohydrodynamical simulations
Physics-motivated Models of Pulsar X-Ray Hotspots: Off-center Dipole Configurations. Recently, it was proposed that an off-center dipole magnetic configuration, together with a nontrivial temperature profile, may be the best model to explain the X-ray light curve of PSR J0030+0451 observed by the Neutron Star Interior Composition Explorer. Using a theoretical model for the electric current density in a force-free pulsar magnetosphere, we compute from first principles the distribution of electric current over the polar cap associated with an off-center magnetic dipole. We then use a simple prescription to compute the resulting temperature distribution, which allows us to derive the observed X-ray light curve. We investigate the role of the volumetric return current region in the polar cap and find that although it does not make a big difference in the case of an aligned dipole, the difference can be bigger in the case of an off-center dipole. Finally, we apply Markov Chain Monte Carlo fitting to the X-ray light curves of pulsars PSR J0030+0451 and PSR J0437─4715 with and without the volumetric return current, and find that our model can reasonably recover the observed X-ray light curves.

Keywords: Neutron stars, X-ray stars, Pulsars