Sazuna/UAT_keywords huggingface dataset:
The Impact of Mass-dependent Stochasticity at Cosmic Dawn. The James Webb Space Telescope is unveiling a surprising lack of evolution in the number densities of ultraviolet (UV)-selected galaxies at redshift z ≳ 10. At the same time, observations and simulations are providing evidence for highly bursty star formation in high-z galaxies, resulting in significant scatter in their UV luminosities. Galaxies in low-mass dark matter halos are expected to experience most stochasticity due to their shallow potential wells. Here, we explore the impact of a mass-dependent stochasticity using a simple analytical model. We assume that scatter in the M UV–M  h  relation increases toward lower halo masses, following the decrease in halo escape velocity,  σUV∼Mh‑1/3 , independent of redshift. Since low-mass halos are more dominant in the early universe, this model naturally predicts an increase in UV luminosity functions (LFs) at high redshifts compared to models without scatter. We make predictions for additional observables, which would be affected by stochasticity and could be used to constrain its amplitude, finding (i) galaxies are less clustered compared to the no-scatter scenario, with the difference increasing at higher-z; (ii) assuming that star-bursting galaxies dominate the ionizing photon budget implies reionization starts earlier and is more gradual compared to the no-scatter case; (iii) at fixed UV magnitude, galaxies should exhibit wide ranges of UV slopes, nebular emission line strengths, and Balmer breaks. Comparing to observations, the mass-dependent stochasticity model successfully reproduces the observed LFs up to z ∼ 12. However, the model cannot match the observed z ∼ 14 LFs, implying additional physical processes enhance star formation efficiency in the earliest galaxies.

Keywords: Cosmology, High-redshift galaxies, Galaxy evolution
A Model of the C IV λ λ1548, 1550 Doublet Line in T Tauri Stars. The C IV doublet in the UV has long been associated with accretion in T Tauri stars. However, it is still unclear where and how the lines are formed. Here, we present a new C IV line model based on the currently available accretion shock and accretion flow models. We assume axisymmetric, dipolar accretion flows with different energy fluxes and calculate the properties of the accretion shock. We use Cloudy to obtain the carbon level populations and calculate the emerging line profiles assuming a plane-parallel geometry near the shock. Our model generally reproduces the intensities and shapes of the C IV emission lines observed from T Tauri stars. We find that the narrow component is optically thin and originates in the postshock, while the broad component is optically thick and emerges from the preshock. We apply our model to seven T Tauri stars from the Hubble Ultraviolet Legacy Library of Young Stars as Essential Standards Director's Discretionary program (ULLYSES), for which the consistently determined accretion shock properties are available. We can reproduce the observations of four stars, finding that the accretion flows are carbon-depleted. We also find that the chromospheric emission accounts for less than 10% of the observed C IV line flux in accreting T Tauri stars. This work paves the way toward a better understanding of hot line formation and provides a potential probe of abundances in the inner disk.

Keywords: Astronomical models, Chemical abundances, Ultraviolet astronomy, T Tauri stars, Protoplanetary disks, Stellar accretion, Radiative transfer
Detection of QPO Soft Lag during the Outburst of Swift J1727.8-1613: Estimation of Intrinsic Parameters from Spectral Study. The recently discovered bright transient black hole candidate Swift J1727.8-1613 is studied in a broad energy range (0.5–79 keV) using combined NICER and NuSTAR data taken on 2023 August 29. A prominent type C quasiperiodic oscillation (QPO) at 0.89 ± 0.01 Hz with its harmonic was observed in NICER data of 0.5–10 keV. Interestingly, the harmonic becomes weaker in the lower energy bands (0.5–1 and 1–3 keV). We also report the first detection of a soft time lag of 0.014 ± 0.001 s at the QPO frequency between harder (3–10 keV) and softer (0.5–3 keV) band photons observed with the NICER/X-ray timing instrument. This indicates that the inclination of the accretion disk in the binary system might be high. From the detailed spectral analysis with the relxill reflection model, we found the disk inclination angle of the source to be ∼85°. We discuss how the accretion flow configuration inferred from spectral analysis can help us understand the origin of QPOs and soft lag in this source.

Keywords: Accretion, Black hole physics, X-ray binary stars, Black holes, X-ray transient sources
An Empirical Calibration of the Tip of the Red Giant Branch Distance Method in the Near Infrared. II. JWST NIRCam Wide Filters. The tip of the red giant branch (TRGB) is a standardizable candle, identifiable as the discontinuity at the bright extreme of the red giant branch (RGB) stars in color–magnitude diagram space. The TRGB-based distance method has been used to measure distances to galaxies out to D ≤ 20 Mpc with the Hubble Space Telescope F814W filter, and is an important rung in the distance ladder to measure the Hubble constant, H 0. In the infrared (IR), the TRGB apparent magnitude ranges from 1–2 mag brighter than in the optical. Now with the James Webb Space Telescope (JWST), the feasible distance range of the TRGB method can reach ∼50 Mpc. However, the IR TRGB luminosity depends to varying degrees on stellar metallicity/age. Here we standardize the TRGB luminosity using stellar colors as a proxy for metallicity/age to derive color-based corrections for the JWST Near-Infrared Camera short-wavelength filters F090W, F115W, and F150W, and the long-wavelength filters F277W, F356W, and F444W. We provide recommended filters for distance measurements depending on the requisite precision. For science requiring high precision (≤1% in distance), we recommend measuring the TRGB in F090W versus F090W ‑ F150W or F115W versus F115W ‑ F277W with the caveat that even with JWST, long integration times will be necessary at farther distances. If lower precision (&gt;1.5% in distance) can be tolerated, or if shorter integration times are desirable, we recommend measuring the TRGB in either F115W or F150W. We do not recommend F444W for precision TRGB measurements due to its lower angular resolution.

Keywords: Galaxy distances, Hubble Space Telescope, Standard candles, Distance indicators, Stellar astronomy, James Webb Space Telescope, Hertzsprung Russell diagram
TEMPLATES: Direct Abundance Constraints for Two Lensed Lyman-break Galaxies. Using integrated spectra for two gravitationally lensed galaxies from the JWST TEMPLATES Early Release Science program, we analyze faint auroral lines, which provide direct measurements of the gas-phase chemical abundance. For the brighter galaxy, SGAS1723+34 (z = 1.3293), we detect the [O III] λ4363, [S III] λ6312, and [O II] λ λ7320, 7330 auroral emission lines, and set an upper limit for the [N II] λ5755 line. For the second galaxy, SGAS1226+21 (z = 2.925), we do not detect any auroral lines, and report upper limits. With these measurements and upper limits, we constrain the electron temperatures in different ionization zones within both of these galaxies. For SGAS1723+34, where auroral lines are detected, we calculate direct oxygen and nitrogen abundances, finding an N/O ratio consistent with observations of nearby (z ∼ 0) galaxies. These observations highlight the potent combination of JWST and gravitational lensing to measure faint emission lines in individual distant galaxies and to directly study the chemical abundance patterns in those galaxies.

Keywords: Strong gravitational lensing, Chemical abundances, Galaxies
Forecasting Constraints from Surface Brightness Fluctuations in Galaxy Clusters. Studies of surface brightness (SB) fluctuations in the intracluster medium present an indirect estimate of turbulent pressure support and associated Mach numbers. While high-resolution X-ray spectroscopy can directly constrain line-of-sight gas motions, including those due to turbulence, such observations are relatively expensive and will be limited to nearby, bright clusters. In this respect, SB fluctuations are the most economical means to constrain turbulent motions at large cluster radii across a range of redshifts and masses. To forecast what current and future X-ray and Sunyaev–Zel'dovich facilities may achieve in SB fluctuation studies, I review and synthesize matters of accuracy and precision with respect to calculating power spectra of SB fluctuations, from which turbulent properties are derived. Balancing concerns of power spectrum accuracy and precision across a range of spatial scales, I propose the use of three annuli with [0, 0.4]R 500, [0.4, 1]R 500, and [1, 1.5]R 500. Adopting these three regions, I calculate the uncertainty in the hydrostatic mass bias,  σbM , that can be achieved for various instruments in several scenarios. I find that Lynx and AtLAST are competitive in their constraints at R 500, while AtLAST should perform better when constraining  σbM  at R 200.

Keywords: Galaxy clusters, Intracluster medium, Astronomical methods
Analysis of the Emission and Morphology of the Pulsar Wind Nebula Candidate HAWC J2031+415. The first TeV γ-ray source with no lower energy counterparts, TeV J2032+4130, was discovered by HEGRA. It appears in the third HAWC catalog as 3HWC J2031+415 and it is a bright TeV γ-ray source whose emission has previously been resolved as two sources: HAWC J2031+415 and HAWC J2030+409. While HAWC J2030+409 has since been associated with the Fermi Large Area Telescope Cygnus Cocoon, no such association for HAWC J2031+415 has yet been found. In this work, we investigate the spectrum and energy-dependent morphology of HAWC J2031+415. We associate HAWC J2031+415 with a γ-ray binary system containing the pulsar PSR J2032+4127 and its companion MT91 213. We study HAWC data to observe their periastron in 2017. Additionally, we perform a combined multiwavelength analysis using radio, X-ray, and γ-ray emission. We conclude that HAWC J2031+415 and, by extension, TeV J2032+4130 are most probably a pulsar wind nebula powered by PSR J2032+4127.

Keywords: Gamma-ray sources, Gamma-ray astronomy, Binary pulsars, Pulsar wind nebulae
Hard X-Ray Spectrum of the Vela Pulsar and Its Wind Nebula Constrained by NuSTAR. We present the analysis of 200 ks NuSTAR observation of the Vela pulsar and the pulsar wind nebula (PWN). The phase-resolved spectra corresponding to two main peaks in the folded pulse profile differ significantly. The spectrum of Peak 1 is significantly harder than that of Peak 2 in qualitative agreement with the earlier Rossi X-ray Timing Explorer results. However, for both spectra, the values of power-law (PL) fit photon indices, Γ, are noticeably larger than the previously reported values. The harder (Peak 1) spectrum has Γ = 1.10 ± 0.15, which is close to those measured for the bright inner jets of the PWN. We used the off-pulse interval to remove the emission from the pulsar and measure the compact PWN spectrum in hard X-rays. We also measured the spectrum from the southwestern region of the PWN, which is resolved by NuSTAR from the compact PWN. For both regions, we fit the NuSTAR spectra by themselves and together with the Chandra X-ray Observatory spectra. We found that the PWN spectrum (for both regions) requires a more complex model than a simple PL. The fits to compact PWN spectrum favor an exponentially cutoff PL model, with E  c  ≈ 50 keV over the broken PL model. The observed synchrotron photon energies imply electrons accelerated to ≈150 TeV.

Keywords: X-ray astronomy, Pulsar wind nebulae, Rotation powered pulsars, Pulsars
A Systematic Search of Distant Superclusters with the Subaru Hyper Suprime-Cam Survey. Superclusters, encompassing environments across a wide range of overdensities, can be regarded as unique laboratories for studying galaxy evolution. Although numerous supercluster catalogs have been published, none of them goes beyond redshift z = 0.7. In this work, we adopt a physically motivated supercluster definition, requiring that superclusters should eventually collapse even in the presence of dark energy. Applying a friends-of-friends (FoF) algorithm to the CAMIRA cluster sample constructed using the Subaru Hyper Suprime-Cam survey data, we have conducted the first systematic search for superclusters at z = 0.5–1.0 and identified 673 supercluster candidates over an area of 1027 deg2. The FoF algorithm is calibrated by evolving N-body simulations to the far future to ensure high purity. We found that these high-z superclusters are mainly composed of two to four clusters, suggesting the limit of gravitationally bound structures in the younger Universe. In addition, we studied the properties of the clusters and brightest cluster galaxies (BCGs) residing in different large-scale environments. We found that clusters associated with superclusters are typically richer, but no apparent dependence of the BCG properties on large-scale structures is found. We also compared the abundance of observed superclusters with mock superclusters extracted from halo light cones, finding that photometric redshift uncertainty is a limiting factor in the performance of superclusters detection.

Keywords: Galaxy clusters, Sky surveys, Large-scale structure of the universe, Superclusters, Catalogs
Event-horizon-scale Imaging of M87* under Different Assumptions via Deep Generative Image Priors. Reconstructing images from the Event Horizon Telescope (EHT) observations of M87*, the supermassive black hole at the center of the galaxy M87, depends on a prior to impose desired image statistics. However, given the impossibility of directly observing black holes, there is no clear choice for a prior. We present a framework for flexibly designing a range of priors, each bringing different biases to the image reconstruction. These priors can be weak (e.g., impose only basic natural-image statistics) or strong (e.g., impose assumptions of black hole structure). Our framework uses Bayesian inference with score-based priors, which are data-driven priors arising from a deep generative model that can learn complicated image distributions. Using our Bayesian imaging approach with sophisticated data-driven priors, we can assess how visual features and uncertainty of reconstructed images change depending on the prior. In addition to simulated data, we image the real EHT M87* data and discuss how recovered features are influenced by the choice of prior.

Keywords: Supermassive black holes, Posterior distribution, Very long baseline interferometry, Event horizons, Prior distribution, Algorithms, Astronomy image processing
Exploring Waveform Variations among Neutron Star Ray-tracing Codes for Complex Emission Geometries. Pulse profile modeling (PPM), the technique used to infer mass, radius, and geometric parameters for rotation-powered millisecond pulsars using data from the Neutron Star Interior Composition Explorer (NICER), relies on relativistic ray-tracing of thermal X-ray photons from hot spots on the neutron star surface to the observer. To verify our ray-tracing codes we have in the past conducted cross tests for simple hot spot geometries, focusing primarily on the implementation of the spacetime model. In this paper, we present verification for test problems that explore the more complex hot spot geometries that are now being employed in the NICER PPM analyses. We conclude that the accuracy of our computed waveforms is in general sufficiently high for analyses of current NICER data sets. We have however identified some extreme configurations where extra care may be needed.

Keywords: Neutron stars, High energy astrophysics, Millisecond pulsars, Gravitation, Rotation powered pulsars, Special relativity, Pulsars, General relativity
A JWST Medium-resolution MIRI Spectrum and Models of the Type Ia Supernova 2021aefx at +415 days. We present a JWST MIRI medium-resolution spectrometer spectrum (5–27 μm) of the Type Ia supernova (SN Ia) SN 2021aefx at +415 days past B-band maximum. The spectrum, which was obtained during the iron-dominated nebular phase, has been analyzed in combination with previous JWST observations of SN 2021aefx to provide the first JWST time series analysis of an SN Ia. We find that the temporal evolution of the [Co III] 11.888 μm feature directly traces the decay of 56Co. The spectra, line profiles, and their evolution are analyzed with off-center delayed-detonation models. Best fits were obtained with white dwarf (WD) central densities of ρ  c  = 0.9‑1.1 × 109 g cm‑3, a WD mass of M WD = 1.33–1.35 M ⊙, a WD magnetic field of ≈106 G, and an off-center deflagration-to-detonation transition at ≈0.5 M ⊙ seen opposite to the line of sight of the observer (‑30°). The inner electron capture core is dominated by energy deposition from γ-rays, whereas a broader region is dominated by positron deposition, placing SN 2021aefx at +415 days in the transitional phase of the evolution to the positron-dominated regime. The formerly "flat-tilted" profile at 9 μm now has a significant contribution from [Ni IV], [Fe II], and [Fe III] and less from [Ar III], which alters the shape of the feature as positrons mostly excite the low-velocity Ar. Overall, the strength of the stable Ni features in the spectrum is dominated by positron transport rather than the Ni mass. Based on multidimensional models, our analysis is consistent with a single-spot, close-to-central ignition with an indication of a preexisting turbulent velocity field and excludes a multiple-spot, off-center ignition.

Keywords: Type Ia supernovae, Supernovae
Formation of Jupiter-mass Binary Objects through Photoerosion of Fragmenting Cores. The recent discovery of tens of Jupiter-mass binary objects (JuMBOs) in the Orion Nebula Cluster (ONC) with the James Webb Space Telescope has intensified the debate on the origin of free-floating planetary mass objects within star-forming regions. The JuMBOs have masses below the opacity limit for fragmentation but have very wide separations (from tens to hundreds of astronomical units), suggesting that they did not form in a similar manner to other substellar mass binaries. Here, we propose that the theory of photoerosion of prestellar cores by Lyman continuum radiation from massive stars could explain the JuMBOs in the ONC. We find that for a range of gas densities the final substellar mass is comfortably within the JuMBO mass range, and the separations of the JuMBOs are consistent with those of more massive (G- and A-type) binaries, which would have formed from the fragmentation of the cores had they not been photoeroded. The photoerosion mechanism is most effective within the H II region(s) driven by the massive star(s). The majority of the observed JuMBOs lie outside of these regions in the ONC, but they may have formed within them and then subsequently migrated due to dynamical evolution.

Keywords: Brown dwarfs, Massive stars, Star forming regions, Free floating planets, Star formation, H II regions
The Challenge of Predicting the Solar Wind Speed near Sunspot Minimum. By applying potential-field source-surface and potential-field current-sheet extrapolations to photospheric field maps from three different observatories, we predict the solar wind speed at Earth for several Carrington rotations during 2018–2021 and compare the results with in situ observations. The predicted speeds are taken to be inversely correlated with the rate of flux-tube expansion inside the source surface, located at a heliocentric distance of 2.5 R ⊙. The results often differ markedly from one observatory to another and are very sensitive to the latitudinal position of the ecliptic relative to the narrow belt of slow wind that surrounds the source-surface neutral line. Our main conclusions are that (1) the magnetograph measurements themselves are a major source of uncertainty in solar wind predictions; (2) these uncertainties are especially large near solar minimum, when Earth is located near the rapid transition between slow and fast wind that occurs on either side of the heliospheric current sheet; (3) comparison of the derived open field regions with observed coronal holes provides a strong, underutilized constraint on wind speed predictions; and (4) the observed polarity of the interplanetary magnetic field provides another important constraint on the location of the source region.

Keywords: Slow solar wind, Heliosphere, Fast solar wind, Space weather, Solar wind, Solar coronal holes, Solar coronal streamers
A Data-driven Magnetohydrodynamic Simulation of the 2011 February 15 Coronal Mass Ejection from Active Region NOAA 11158. We present a boundary data-driven magnetohydrodynamic (MHD) simulation of the 2011 February 15 coronal mass ejection (CME) event of Active Region NOAA 11158. The simulation is driven at the lower boundary with an electric field derived from the normal magnetic field and the vertical electric current measured from the Solar Dynamics Observatory (SDO) Helioseismic Magnetic Imager vector magnetograms. The simulation shows the buildup of a pre-eruption coronal magnetic field that is close to the nonlinear force-free field extrapolation, and it subsequently develops multiple eruptions. The sheared/twisted field lines of the pre-eruption magnetic field show qualitative agreement with the brightening loops in the SDO Atmospheric Imaging Assembly (AIA) hot passband images. We find that the eruption is initiated by the tether-cutting reconnection in a highly sheared field above the central polarity inversion line and a magnetic flux rope with dipped field lines forms during the eruption. The modeled erupting magnetic field evolves to develop a complex structure containing two distinct flux ropes and produces an outgoing double-shell feature consistent with the Solar Terrestrial Relations Observatory B/Extreme UltraViolet Imager observation of the CME. The foot points of the erupting field lines are found to correspond well with the dimming regions seen in the SDO/AIA observation of the event. These agreements suggest that the derived electric field is a promising way to drive MHD simulations to establish the realistic pre-eruption coronal field based on the observed vertical electric current and model its subsequent dynamic eruption.

Keywords: The Sun, Magnetohydrodynamics, Solar coronal mass ejections, Magnetohydrodynamical simulations
Binary Disruption and Ejected Stars from Hierarchical Star Cluster Assembly. We simulate mergers between star clusters embedded within their natal giant molecular cloud. We extract initial conditions from cloud-scale simulations of cluster formation and introduce different prescriptions for primordial binaries. We find that simulations that do not include primordial binaries result in a larger fraction of unbound stars than simulations that include a prescription for binaries based on observations. We also find a preferred direction of motion for stars that become unbound during the merger. Subcluster mergers within realistic gas environments promote binary disruption, while mergers between idealized, gas-rich spherical clusters do not produce the same disruption. Binary systems with smaller semimajor axes are disrupted in simulations of subcluster mergers within their natal environment compared to simulations that do not include the realistic gas environment. We conclude that binary disruption and the production of an anisotropic distribution of unbound stars are the natural consequences of subcluster mergers during star cluster assembly.

Keywords: Binary stars, Star forming regions, Young star clusters, Stellar dynamics, Star clusters