adsabs/SciX_UAT_keywords huggingface dataset:
Recovering Age-Metallicity Distributions from Integrated Spectra: Validation with MUSE Data of a Nearby Nuclear Star Cluster

Current instruments and spectral analysis programs are now able to decompose the integrated spectrum of a stellar system into distributions of ages and metallicities. The reliability of these methods has rarely been tested on nearby systems with resolved stellar ages and metallicities. Here we derive the age-metallicity distribution of M54, the nucleus of the Sagittarius dwarf spheroidal galaxy, from its integrated Multi-Unit Spectroscopic Explorer (MUSE) spectrum. We find a dominant old (8-14 Gyr), metal-poor (-1.5 dex) component and a young (1 Gyr), metal-rich (+0.25 dex) component—consistent with the complex stellar populations measured from individual stars in the same MUSE data set. There is excellent agreement between the (mass-weighted) average age and metallicity of the resolved and integrated analyses. Differences are only 3% in age and 0.2 dex metallicity. By co-adding individual stars to create M54's integrated spectrum, we show that the recovered age-metallicity distribution is insensitive to the magnitude limit of the stars or the contribution of blue horizontal branch stars—even when including additional blue wavelength coverage from the WiFeS Atlas of Galactic Globular cluster Spectra survey. However, we find that the brightest stars can induce the spurious recovery of an old (>8 Gyr), metal-rich (+0.25 dex) stellar population, which is otherwise not expected from our understanding of chemical enrichment in M54. The overall derived stellar mass-to-light ratio of M54 is M/LV = 1.46 with a scatter of 0.22 across the field of view, which we attribute to the stochastic contribution of a young, metal-rich component. These findings provide strong evidence that complex stellar population distributions can be reliably recovered from integrated spectra of extragalactic systems.

Keywords: galaxy stellar content; stellar populations; galaxy nuclei; metallicity; galaxy ages; mass-to-light ratio; galaxy chemical evolution
Boundary of the Distribution of Solar Wind Proton Beta versus Temperature Anisotropy

The frequency distribution of solar wind protons, measured in the vicinity of Earth's orbit, is customarily plotted in (β ∥, T ⊥/T ∥) phase space. Here, T ⊥/T ∥ is the ratio of perpendicular and parallel temperatures, and β ∥ = 8π nT ∥/B 2 is the ratio of parallel thermal energy to background magnetic field energy, the so-called "parallel beta," with ⊥ and ∥ denoting directions with respect to the ambient magnetic field. Such a frequency distribution, plotted as a two-dimensional histogram, forms a peculiar rhombic shape defined with an outer boundary in the said phase space. Past studies reveal that the threshold conditions for temperature anisotropy–driven plasma instability partially account for the boundary on the high-β ∥ side. The low-β ∥ side remains largely unexplained despite some efforts. Work by Vafin et al. recently showed that certain contours of collisional relaxation frequency, ν pp, when parameterized by T ⊥/T ∥ and β ∥, could match the overall shape of the left-hand boundary, thus suggesting that the collisional relaxation process might be closely related to the formation of the left-hand boundary. The present paper extends the analysis by Vafin et al. and carries out the dynamical computation of the collisional relaxation process for an ensemble of initial proton states with varying degrees of anisotropic temperatures. The final states of the relaxed protons are shown to closely match the observed boundary to the left of the (β ∥, T ⊥/T ∥) phase space. When coupled with a similar set of calculations for the ensemble in the collective instability regime, it is found that the combined collisional/collective effects provide the baseline explanation for the observation.

Keywords: solar wind; interplanetary physics; space plasmas; heliosphere; plasma physics
Stellar Cruise Control: Weakened Magnetic Braking Leads to Sustained Rapid Rotation of Old Stars

Despite a growing sample of precisely measured stellar rotation periods and ages, the strength of magnetic braking and the degree of departure from standard (Skumanich-like) spin-down have remained persistent questions, particularly for stars more evolved than the Sun. Rotation periods can be measured for stars older than the Sun by leveraging asteroseismology, enabling models to be tested against a larger sample of old field stars. Because asteroseismic measurements of rotation do not depend on starspot modulation, they avoid potential biases introduced by the need for a stellar dynamo to drive starspot production. Using a neural network trained on a grid of stellar evolution models and a hierarchical model-fitting approach, we constrain the onset of weakened magnetic braking (WMB). We find that a sample of stars with asteroseismically measured rotation periods and ages is consistent with models that depart from standard spin-down prior to reaching the evolutionary stage of the Sun. We test our approach using neural networks trained on model grids produced by separate stellar evolution codes with differing physical assumptions and find that the choices of grid physics can influence the inferred properties of the braking law. We identify the normalized critical Rossby number Rocrit/Ro⊙ = 0.91 ± 0.03 as the threshold for the departure from standard rotational evolution. This suggests that WMB poses challenges to gyrochronology for roughly half of the main-sequence lifetime of Sun-like stars.

Keywords: stellar evolution; stellar rotation; stellar magnetic fields; asteroseismology; stellar properties; stellar ages; solar analogs
Solar Spicules, Filigrees, and Solar Wind Switchbacks

Spicules, the smallest observable jetlike dynamic features ubiquitous in the chromosphere, are supposedly an important potential source for small-scale solar wind transients, with supporting evidence yet needed. We studied the high-resolution Hα images (0.″10) and magnetograms (0.″29) from the Big Bear Solar Observatory to find that spicules are an ideal candidate for the solar wind magnetic switchbacks detected by the Parker Solar Probe (PSP). It is not that spicules are a miniature of coronal jets, but that they have unique properties not found in other solar candidates in explaining solar origin of switchbacks. (1) The spicules under this study originate from filigrees, all in a single magnetic polarity. Since filigrees are known as footpoints of open fields, the spicule guiding field lines can form a unipolar funnel, which is needed to create an SB patch, a group of field lines that switch from one common base polarity to the other polarity. (2) The spicules come in a cluster lined up along a supergranulation boundary, and the simulated waiting times from their spatial intervals exhibit a number distribution continuously decreasing from a few seconds to ∼30 minutes, similar to that of switchbacks. (3) From a time–distance map for spicules, we estimate their occurrence rate as 0.55 spicules Mm‑2 s‑1, which is sufficiently high for detection by PSP. In addition, the dissimilarity of spicules with coronal jets, including the absence of base brightening and low correlation with EUV emission, is briefly discussed.

Keywords: solar chromosphere; solar wind; solar magnetic fields
Evolution of the Galaxy Merger Fraction in the CLAUDS+HSC-SSP Deep Fields

We estimate the evolution of the galaxy-galaxy merger fraction for M⋆ > 1010.5M⊙ galaxies over 0.25 < z < 1 in the ∼18.6 deg2 deep CLAUDS+HSC-SSP surveys. We do this by training a Random Forest Classifier to identify merger candidates from a host of parametric morphological features, and then visually follow-up likely merger candidates to reach a high-purity, high-completeness merger sample. Correcting for redshift-dependent detection bias, we find that the merger fraction at z = 0 is 1.0% ± 0.2%, that the merger fraction evolves as (1 + z)2.3 ± 0.4, and that a typical massive galaxy has undergone ∼0.3 major mergers since z = 1. This pilot study illustrates the power of very deep ground-based imaging surveys combined with machine learning to detect and study mergers through the presence of faint, low surface brightness merger features out to at least z ∼ 1.

Keywords: galaxy mergers; galaxy evolution; galaxy interactions
JWST Insight into a Lensed HST-dark Galaxy and Its Quiescent Companion at z = 2.58

Using the novel James Webb Space Telescope (JWST)/NIRCam observations in the A2744 field, we present a first spatially resolved overview of a Hubble Space Telescope (HST)-dark galaxy, spectroscopically confirmed at z = 2.58 with magnification μ ≈ 1.9. While being largely invisible at ~1 μm with NIRCam, except for sparse clumpy substructures, the object is well detected and resolved in the long-wavelength bands with a spiral shape clearly visible in F277W. By combining ancillary Atacama Large Millimeter/submillimeter Array (ALMA) and Herschel data, we infer that this object is an edge-on dusty spiral with an intrinsic stellar mass log (M */M ⊙) ~ 11.3 and a dust-obscured star formation rate ~300 M ⊙ yr-1. A massive quiescent galaxy (log (M */M ⊙) ~ 10.8) with tidal features lies 2.″0 away (r ~ 9 kpc), at a consistent redshift as inferred by JWST photometry, indicating a potential major merger. The dusty spiral lies on the main sequence of star formation, and shows high dust attenuation in the optical (3 < A V < 4.5). In the far-infrared, its integrated dust spectral energy distribution is optically thick up to λ 0 ~ 500 μm, further supporting the extremely dusty nature. Spatially resolved analysis of the HST-dark galaxy reveals a largely uniform A V ~ 4 area spanning ~57 kpc2, which spatially matches to the ALMA 1 mm continuum emission. Accounting for the surface brightness dimming and the depths of current JWST surveys, unlensed analogs of the HST-dark galaxy at z > 4 would be only detectable in F356W and F444W in an UNCOVER-like survey, and become totally JWST-dark at z ~ 6. This suggests that detecting highly attenuated galaxies in the Epoch of Reionization might be a challenging task for JWST.

Keywords: active galaxies; disk galaxies
Large-scale Variation in Reionization History Caused by Baryon-Dark Matter Streaming Velocity

At cosmic recombination, there was supersonic relative motion between baryons and dark matter, which originated from baryonic acoustic oscillations in the early universe. This motion has been considered to have a negligible impact on the late stage of cosmic reionization because the relative velocity quickly decreases. However, recent studies have suggested that the recombination in gas clouds smaller than the local Jeans mass (≲108 M⊙) can affect the reionization history by boosting the number of ultraviolet photons required for ionizing the intergalactic medium. Motivated by this, we performed a series of radiation-hydrodynamic simulations to investigate whether the streaming motion can generate variation in the local reionization history by smoothing out clumpy small-scale structures and lowering the ionizing photon budget. We found that the streaming velocity can add a variation of Δze ∼ 0.05-0.5 in the end-of-reionization redshift, depending on the level of X-ray preheating and the time evolution of ionizing sources. The variation tends to be larger when the ionizing efficiency of galaxies decreases toward later times. Given the long spatial fluctuation scales of the streaming motion (≳100 Mpc), it can help to explain the Lyα opacity variation observed from quasars and leave large-scale imprints on the ionization field of the intergalactic medium during the reionization. The pre-reionization heating by X-ray sources is another critical factor that can suppress small-scale gas clumping and can diminish the variation in ze introduced by the streaming motion.

Keywords: reionization; early universe
A Significantly Neutral Intergalactic Medium Around the Luminous z = 7 Quasar J0252-0503

Luminous z ≥ 7 quasars provide direct probes of the evolution of supermassive black holes (SMBHs) and the intergalactic medium (IGM) during the epoch of reionization (EoR). The Lyα damping wing absorption imprinted by neutral hydrogen in the IGM can be detected in a single EoR quasar spectrum, allowing the measurement of the IGM neutral fraction toward that line of sight. However, damping wing features have only been detected in two z > 7 quasars in previous studies. In this paper, we present new high-quality optical and near-infrared spectroscopy of the z = 7.00 quasar DES J025216.64-050331.8 obtained with Keck/Near-Infrared Echellette Spectrometer and Gemini/GMOS. By using the Mg II single-epoch virial method, we find that it hosts a $(1.39\pm 0.16)\times {10}^{9}\,{M}_{\odot }$ SMBH accreting at an Eddington ratio of λEdd = 0.7 ± 0.1, consistent with the values seen in other luminous z ∼ 7 quasars. Furthermore, the Lyα region of the spectrum exhibits a strong damping wing absorption feature. The lack of associated metal absorption in the quasar spectrum indicates that this absorption is imprinted by a neutral IGM. Using a state-of-the-art model developed by Davies et al., we measure a volume-averaged neutral hydrogen fraction at z = 7 of $\langle {X}_{{\rm{H}}{\rm{I}}}\rangle ={0.70}_{-0.23}^{+0.20}{(}_{-0.48}^{+0.28})$ within 68% (95%) confidence intervals when marginalizing over quasar lifetimes of ${10}^{3}\leqslant {t}_{{\rm{Q}}}\leqslant {10}^{8}\,\mathrm{yr}$ . This is the highest IGM neutral fraction yet measured using reionization-era quasar spectra.

Keywords: intergalactic medium; quasars; quasar absorption line spectroscopy; reionization; supermassive black holes; early universe
Overstable Convective Modes in a Polytropic Stellar Atmosphere

Within the convection zone of a rotating star, the presence of the Coriolis force stabilizes long-wavelength convective modes. These modes, which would have been unstable if the star lacked rotation, are called overstable convective modes or thermal Rossby waves. We demonstrate that the Sun's rotation rate is sufficiently rapid that the lower half of its convection zone could possess overstable modes. Further, we present an analytic solution for atmospheric waves that reside within a polytropic stratification. We explore in detail the properties of the overstable and unstable wave modes that exist when the polytrope is weakly unstable to convective overturning. Finally, we discuss how the thermal Rossby waves that reside within the convection zone of a star might couple with the prograde branch of the g modes that are trapped within the star's radiative zone. We suggest that such coupling might enhance the photospheric visibility of a subset of the Sun's g modes.

Keywords: stellar convective zones; solar convective zone; polytropes; stellar oscillations; solar oscillations; stellar rotation; solar rotation; internal waves; asteroseismology; helioseismology; solar interior
Supernova Explosions of the Lowest-mass Massive Star Progenitors

We here focus on the behavior of supernovae that technically explode in 1D (spherical symmetry). When simulated in 3D, however, the outcomes of representative progenitors of this class are quite different in almost all relevant quantities. In 3D, the explosion energies can be 2 to 10 times higher, and there are correspondingly large differences in the 56Ni yields. These differences between the 3D and 1D simulations reflect in part the relative delay to explosion of the latter and in the former the presence of protoneutron star convection that boosts the driving neutrino luminosities by as much as ∼50% at later times. In addition, we find that the ejecta in 3D models are more neutron-rich, resulting in significant weak r-process and 48Ca yields. Furthermore, we find that in 3D the core is an interesting, though subdominant, source of acoustic power. In summary, we find that though a model might be found theoretically to explode in 1D, one must perform supernova simulations in 3D to capture most of the associated observables. The differences between 1D and 3D models are just too large to ignore.

Keywords: core-collapse supernovae; nucleosynthesis; supernova dynamics
The MASSIVE Survey. XV. A Stellar Dynamical Mass Measurement of the Supermassive Black Hole in Massive Elliptical Galaxy NGC 1453

We present a new stellar dynamical mass measurement (M_{BH}) of the supermassive black hole (SMBH) in NGC 1453, a fast-rotating massive elliptical galaxy in the MASSIVE survey. We measure stellar kinematics in 135 spatial bins in the central 1.5 kpc × 2 kpc region of the galaxy using high signal-to-noise ratio (S/N ∼ 130) spectra from the Gemini-North GMOS integral field spectrograph (IFS). Combining with wide-field IFS kinematics out to ∼3 effective radii and stellar light distributions from Hubble Space Telescope Wide Field Camera 3 images, we perform Schwarzschild orbit-based mass modeling in the axisymmetric limit to constrain the mass components in NGC 1453. The best-fit black hole mass is M_{BH}=(2.9± 0.4)× 10^{9} M_{⊙}; the mass models without a central black hole are excluded at the 8.7σ level. The NGC 1453 black hole lies within the intrinsic scatter of the SMBH and galaxy scaling relations, unlike three other galaxies hosting ≳ 10^{10} M_{⊙} SMBHs in the MASSIVE sample. The high-S/N GMOS spectra enable us to determine eight moments of the Gauss-Hermite expansion of the line-of-sight velocity distributions (LOSVDs), which are used as constraints in the orbit modeling. The stellar orbits in the mass models are further constrained to produce negligible h9 through h12 to minimize spurious behavior in the LOSVDs. We show that truncating the series at h4, as was often done in prior work, leads to a much weaker constraint on the inferred M_{BH} for NGC 1453. Furthermore, we discuss precautions and modifications that are needed to achieve axisymmetry in triaxial orbit codes that use the Schwarzschild method to sample the start space of stellar orbits in triaxial gravitational potentials.

Keywords: elliptical galaxies; galaxies; galaxy dynamics; galaxy evolution; galaxy kinematics; galaxy structure; dark matter
Messenger Monte Carlo MAPPINGS V (M3)-A Self-consistent, Three-dimensional Photoionization Code

The Messenger Interface Monte Carlo Mappings V (M3) is a photoionization code adopting the fully self-consistent Monte Carlo radiative transfer (MCRT) technique, which presents a major advance over previous photoionization models with simple geometries. M3 is designed for modeling nebulae in arbitrary three-dimensional geometries. In this paper, we describe the MCRT technique and the microphysics implemented in M3, including photoionization, collisional ionization, free-free and free-bound recombination, and two-photon radiation. We put M3 through the Lexington/Meudon benchmarks to test the reliability of the new code. We apply M3 to three H II region models with fiducial geometries, demonstrating that M3 is capable of dealing with nebulae with complex geometries. M3 is a promising tool for understanding emission-line behavior in the era of SDSS-V/LVM and James Webb Space Telescope, which will provide high-quality data of spatially resolved nearby H II regions and highly turbulent local and high-redshift H II regions.

Keywords: interstellar medium; galaxy physics; high-redshift galaxies; starburst galaxies
Eruptivity Criteria for Solar Coronal Flux Ropes in Magnetohydrodynamic and Magnetofrictional Models

We investigate which scalar quantity or quantities can best predict the loss of equilibrium and subsequent eruption of magnetic flux ropes in the solar corona. Our models are initialized with a potential magnetic arcade, which is then evolved by means of two effects on the lower boundary: first, a gradual shearing of the arcade, modeling differential rotation on the solar surface; and second, supergranular diffusion. These result in flux cancellation at the polarity inversion line and the formation of a twisted flux rope. We use three model setups: full magnetohydrodynamics (MHD) in cartesian coordinates, and the magnetofrictional (MF) model in both cartesian and polar coordinates. The flux ropes are translationally invariant, allowing for very fast computational times and thus a comprehensive parameter study, comprising hundreds of simulations and thousands of eruptions. Similar flux rope behavior is observed using either magnetofriction or MHD, and there are several scalar criteria that could be used as proxies for eruptivity. The most consistent predictor of eruptions in either model is the squared current in the axial direction of the rope, normalized by the relative helicity, although a variation on the previously proposed eruptivity index is also found to perform well in both the MF and MHD simulations.

Keywords: solar corona; solar magnetic fields; solar coronal mass ejections
Simulating the Sensitivity to Stellar Point Sources of Chandra X-Ray Observations

The Chandra Cygnus OB2 Legacy Survey is a wide and deep X-ray survey of the nearby and massive Cygnus OB2 association. The survey has detected ~8000 X-ray sources, the majority of which are pre-main-sequence X-ray-emitting young stars in the association itself. To facilitate quantitative scientific studies of these sources, as well as the underlying OB association, it is important to understand the sensitivity of the observations and the level of completeness the observations have obtained. Here we describe the use of a hierarchical Monte Carlo simulation to achieve this goal by combining the empirical properties of the observations, analytic estimates of the source verification process, and an extensive set of source detection simulations. We find that our survey reaches a 90% completeness level for a pre-main-sequence population at the distance of Cyg OB2 at an X-ray luminosity of 4 × 1030 erg s-1 and a stellar mass of 1.3 M ⊙ for a randomly distributed population. For a spatially clustered population such as Cyg OB2 the 90% completeness level is reached at 1.1 M ⊙ instead, as the sources are more concentrated in areas of our survey with a high exposure. These simulations can easily be adapted for use with other X-ray observations and surveys, and we provide X-ray detection efficiency curves for a very wide array of source and background properties to allow these simulations to be easily exploited by other users.

Keywords: x-ray stars; pre-main sequence stars
Characteristics of Magnetic Holes in the Solar Wind Revealed by Parker Solar Probe

We present a statistical analysis for the characteristics and radial evolution of linear magnetic holes (LMHs) in the solar wind from 0.166 to 0.82 au using Parker Solar Probe observations of the first two orbits. It is found that the LMHs mainly have a duration less than 25 s and the depth is in the range from 0.25 to 0.7. The durations slightly increase and the depths become slightly deeper with the increasing heliocentric distance. Both the plasma temperature and the density for about 50% of all events inside the holes are higher than the ones surrounding the holes. The average occurrence rate is 8.7 events day-1, much higher than that of the previous observations. The occurrence rate of the LMHs has no clear variation with the heliocentric distance (only a slight decreasing trend with the increasing heliocentric distance), and has several enhancements around ∼0.525 and ∼0.775 au, implying that there may be new locally generated LMHs. All events are segmented into three parts (i.e., 0.27, 0.49, and 0.71 au) to investigate the geometry evolution of the linear magnetic holes. The results show that the geometry of LMHs are prolonged both across and along the magnetic field direction from the Sun to the Earth, while the scales across the field extend a little faster than along the field. The present study could help us understand the evolution and formation mechanism of the LMHs in the solar wind.

Keywords: solar wind; solar physics; interplanetary magnetic fields; solar magnetic fields