adsabs/SciX_UAT_keywords huggingface dataset:
A JWST/NIRSpec Exploration of the Connection between Ionization Parameter, Electron Density, and Star-formation-rate Surface Density in z = 2.7-6.3 Galaxies

We examine the factors responsible for the variation in the ionization parameter (U) of high-redshift star-forming galaxies based on medium-resolution JWST/NIRSpec observations obtained by the Cosmic Evolution Early Release Science survey. The sample consists of 48 galaxies with redshifts z spec = 2.7-6.3, which are largely representative of typical galaxies at these redshifts. The [S II] λ λ6718, 6733 doublet is used to estimate electron densities (n e ), and dust-corrected Hα luminosities are used to compute ionizing photon rates (Q). Using composite spectra of galaxies in bins of [O III] λ λ4960, 5008/[O II] λ λ3727, 3730 (O32) as a proxy for U, we determine that galaxies with higher O32 have <n e > ≃ 500 cm-3 that are ≳5 × larger than that of lower-O32 galaxies. We do not find a significant difference in <Q> between low- and high-O32 galaxies. Photoionization modeling indicates a large spread in $\mathrm{log}U$ of ≈1.5 dex at a fixed Z neb. On the other hand, the data indicate a highly significant correlation between U and star-formation-rate surface density (ΣSFR), which appears to be redshift invariant at z ~ 1.6-6.3, and possibly up to z ~ 9.5. We consider several avenues through which metallicity and ΣSFR (or gas density) may influence U, including variations in n e and Q, internal dust extinction of ionizing photons, and the effects of gas density on the volume filling fraction. Based on these considerations, we conclude that gas density may play a more central role than metallicity in modulating U at these redshifts.

Keywords: high-redshift galaxies; starburst galaxies; interstellar abundances; stellar abundances; h ii regions; interstellar medium
Background Microwave Emission and Microflares in Young Active Region 12635

The goal of this work is to study the atmospheric heating above isolated AR 12635 during a period in which a quasistationary increase in microwave and soft X-ray emission is combined with a series of B- and C-class microflares. Analysis of photospheric vector magnetograms showed that an increase in the SXR brightness lasting 14 hours was observed during the simplification of the magnetic structure and the growth of vertical currents in the head part of the active region. A long-term increase of SXR and microwave emission occurred when the total unsigned vertical current exceeded the critical value and coincided in time with the increased level of the emission measure calculated from the GOES X-ray data. Against the background of quasistationary emission, microflares lasting 6-10 minutes occurred. In the hard X-ray range, bursts are recorded with RHESSI channels up to 25 keV. In microwave emission, pulsed and smooth components are distinguished during microflares. The first component was recorded in the 4.5-7.5 GHz range at the beginning of microflares and it is generated by a small population of relativistic electrons by the gyrosychrotron mechanism. The smooth component of the bursts dominated at 17 GHz and was emitted by bremsstrahlung. It is shown that the sources of quasistationary emission and microflares coincide with each other and with the bremsstrahlung source calculated from the differential emission measure obtained from the EUV maps. Coronal magnetic field reconstruction shows that the release of energy on both timescales occurs in a stably existing bundle of magnetic field lines.

Keywords: solar flares
Modeling the IRIS Lines During a Flare. I. The Blue-wing Enhancement in the Mg II k Line

The Interface Region Imaging Spectrograph (IRIS) Mg II k line serves as a very good tool to diagnose the heating processes in solar flares. Recent studies have shown that apart from the usual red asymmetries that are interpreted as the result of condensation downflows, this line could also show a blue-wing enhancement. To investigate how such a blue asymmetry is formed, we perform a grid of radiative hydrodynamic simulations and calculate the corresponding line profiles. We find that such a spectral feature is likely to originate from the upward plasma motion in the upper chromosphere. However, the formation region that is responsible for the blue-wing enhancement could be located in an evaporation region, in an upward-moving blob, and even an upward-moving condensation region. We discuss how the electron beam parameters affect these different dynamics of the atmosphere.

Keywords: solar chromosphere; solar flare spectra; radiative transfer simulations
The Resolved Star Formation Law in NGC 7469 from JWST, ALMA, and VLA

We investigate the star formation process within the central 3.3 kpc region of the nearby luminous infrared Seyfert NGC 7469, probing scales ranging from 88 to 330 pc. We combine JWST/MIRI imaging with the F770W filter, with CO(2 – 1) and the underlying 1.3 mm dust continuum data from the Atacama Large Millimeter/submillimeter Array, along with Karl G. Jansky Very Large Array radio continuum observations at 22 GHz. NGC 7469 hosts a starburst ring which dominates the overall star formation activity. We estimate the global star formation rate (SFR) ∼ 11.5 M ⊙ yr‑1 from the radio at 22 GHz, and a cold molecular gas mass M(H2) ∼ 6.4 × 109 M ☉ from the CO(2 – 1) emission. We find that the 1.3 mm map shows a morphology remarkably similar to those traced by the 22 GHz and the 7.7 μm polycyclic aromatic hydrocarbon (PAH) emission observed with JWST. The three tracers reproduce the morphology of the starburst ring with good agreement. We further investigate the correlations between the PAHs, the SFR, and the cold molecular gas. We find a stronger correlation of the PAHs with star formation than with CO, with steeper correlations within the starburst ring (n > 2) than in the outer region (n < 1). We derive a correlation between the SFR and the cold molecular gas mass surface densities, the Kennicutt–Schmidt (K-S) star formation law. Comparisons with other galaxy populations, including starburst galaxies and active galactic nuclei, highlighted that NGC 7469 exhibits an intermediate behavior to the K-S relations found for these galaxy populations.

Keywords: agn host galaxies; molecular gas; star formation; interstellar medium
The Cosmic Ultraviolet Baryon Survey (CUBS). VIII. Group Environment of the Most Luminous Quasars at z ≈ 1

We investigate the group-scale environment of 15 luminous quasars (luminosity L 3000 > 1046 erg s‑1) from the Cosmic Ultraviolet Baryon Survey (CUBS) at redshift z ≈ 1. Using the Multi Unit Spectroscopic Explorer integral field spectrograph on the Very Large Telescope, we conduct a deep galaxy redshift survey in the CUBS quasar fields to identify group members and measure the physical properties of individual galaxies and galaxy groups. We find that the CUBS quasars reside in diverse environments. The majority (11 out of 15) of the CUBS quasars reside in overdense environments with typical halo masses exceeding 1013 M ⊙, while the remaining quasars reside in moderate-size galaxy groups. No correlation is observed between overdensity and redshift, black hole (BH) mass, or luminosity. Radio-loud quasars (5 out of 15 CUBS quasars) are more likely to be in overdense environments than their radio-quiet counterparts in the sample, consistent with the mean trends from previous statistical observations and clustering analyses. Nonetheless, we also observe radio-loud quasars in moderate groups and radio-quiet quasars in overdense environments, indicating a large scatter in the connection between radio properties and environment. We find that the most UV luminous quasars might be outliers in the stellar mass-to-halo mass relations or may represent departures from the standard single-epoch BH relations.

Keywords: quasars; galaxy groups; redshift surveys
An Iterative OLA Method for Inversion of Solar Spectropolarimetric Data. I. Single- and Multiple-variable Inversions of Thermodynamic Quantities

This paper describes an adaptation of the Optimally Localized Averaging (OLA) inversion technique, originally developed for geo- and helioseismological applications, to the interpretation of solar spectroscopic data. It focuses on inverting the thermodynamical properties of the solar atmosphere, assuming that the atmosphere and radiation field are in local thermodynamic equilibrium (LTE). We leave inversions of magnetic field and non-LTE inversions for future work. The advantage with the OLA method is that it computes solutions that are optimally depth resolved with minimal crosstalk error between variables. Additionally, the method allows for direct assessment of the vertical resolution of the inverted solutions. The primary challenges faced when adapting the method to spectroscopic inversions originate with the possible large-amplitude differences between the atmospheric model used to initiate the inversion and the underlying atmosphere it aims to recover, necessitating the development of an iterative scheme. Here, we describe the iterative OLA method we have developed for both single and multivariable inversions and demonstrate its performance on simulated data and synthesized spectra. We note that, when carrying out multivariable inversions, employing response function amplification factors can address the inherent spectral sensitivity bias that makes it hard to invert for less spectrally sensitive variables. The OLA method can, in most cases, reliably invert as well as or better than the frequently employed Stokes Inversion based on Response functions (SIR) scheme, but some difficulties remain. In particular, the method struggles to recover large-scale offsets in the atmospheric stratification. We propose future strategies to improve this aspect.

Keywords: radiative transfer; spectropolarimetry; helioseismology; solar physics
Asteroseismology of the DAV Star L19-2

L19-2 is a DAV star, which was intermittently observed from 1976 to 2013. Five independent pulsation modes of 350, 192, 143, 118, and 113 s are identified. The five modes can be used to constrain the fitting models. The rates of period change can be obtained through the O-C method for the modes of 192 and 113 s, which can be used to study the evolution effect of DAV stars. Using the White Dwarf Evolution Code (WDEC; 2018 version), a large sample of DAV star models are evolved. The theoretical modes are calculated and used to fit the observed modes. After fine model fittings, we obtain an optimal model with an absolute difference of Φ = 0.06 s. By parameterizing the core oxygen profile, the WDEC procedure can greatly reduce the fitting error of asteroseismological models. According to our optimal model, the distance obtained through the model luminosity is only 1% different from that reported by the Gaia Data Release 2. L19-2 is a massive and hot DAV star with a relatively thick H atmosphere and a thick He layer. The stellar parameters and the rates of period change of our optimal model are slightly modified from that of the previous work. Our optimal model has a large central oxygen abundance. The central oxygen abundance is strongly correlated with the previous physical process of stellar evolution. A lot of asteroseismological work on white dwarfs presents an opportunity to explore the progenitor stars.

Keywords: asteroseismology; white dwarf stars; da stars
X-Ray Monitoring of Gravitationally Lensed Radio-loud Quasars with Chandra

In this work, we calculated the sizes of unresolved X-ray emission regions in three gravitationally lensed radio-loud quasars, B 1422+231, MG J0414+0534, and Q 0957+561, using a combination of imaging and spectral analysis on the X-ray data taken from the Chandra X-Ray Observatory. We tentatively detected FeKα emission lines in MG J0414+0534 and Q 0957+561 with over 95% significance, whereas, we did not significantly detect FeKα emission in B 1422+231. We constructed differential microlensing light curves from absorption corrected count rates. We subsequently performed a microlensing analysis on the X-ray microlensing light curves to measure the X-ray source sizes in rest frame soft (0.83-3.6 keV), hard (3.6-21.8 keV), and full (0.83-21.8 keV) bands, based on either Bayesian or maximum likelihood probabilities. For B 1422+231, sizes from the two methods are consistent with each other, ${R}_{{\rm{X}}}^{\mathrm{hard}}/{R}_{G}=6.17\pm 5.48$ (Bayesian), 11.81 ± 3.75 (maximum likelihood), where ${R}_{G}={{GM}}_{\mathrm{BH}}/{c}^{2})$ . However, for MG J0414+0534 and Q 0957+561, the two methods yield substantially different results suggesting that more frequently sampled data with better signal-to-noise ratio are needed to measure the source size for these two objects. Comparing the acquired size values with the radio-quiet sample in the literature we found that our results are consistent with X-ray source size scaling approximately as RX ∝ MBH with the mass of the central supermassive black hole. Our Bayesian analysis results also indicate that radio-loud quasars tend to have larger unresolved X-ray emission sizes compared to the radio-quiet ones, suggesting a more prominent jet contribution.

Keywords: radio loud quasars; x-ray active galactic nuclei; quasar microlensing; strong gravitational lensing; x-ray astronomy
Atacama Compact Array Measurements of the Molecular Mass in the NGC 5044 Cooling-flow Group

The fate of cooling gas in the centers of galaxy clusters and groups is still not well understood, as is also the case for the complex processes of triggering star formation in central dominant galaxies, reheating of cooled gas by active galactic nuclei (AGN), and the triggering or "feeding" of supermassive black hole outbursts. We present CO observations of the early-type galaxy NGC 5044, which resides at the center of an X-ray bright group with a moderate cooling flow. For our analysis we combine CO(2-1) data from the 7 m antennae of the Atacama Compact Array (ACA) and the ACA total power array (TP). We demonstrate, using the 7 m array data, that we can recover the total flux inferred from IRAM 30 m single-dish observations, which corresponds to a total molecular mass of about 4 × 107M⊙. Most of the recovered flux is blueshifted with respect to the galaxy rest frame and is extended on kiloparsec-scales, suggesting low filling factor dispersed clouds. We find eight concentrations of molecular gas out to a radius of 10″ (1.5 kpc), which we identify with giant molecular clouds. The total molecular gas mass is more centrally concentrated than the X-ray emitting gas, but is extended in the northeast-southwest direction beyond the IRAM 30 m beam. We also compare the spatial extent of the molecular gas to the Hα emission: The CO emission coincides with the very bright Hα region in the center. We do not detect CO emission in the fainter Hα regions. Furthermore, we find two CO absorption features spatially located at the center of the galaxy, within 5 pc projected distance of the AGN, infalling at 255 and 265 km s-1 relative to the AGN. This indicates that the two giant molecular clouds seen in absorption are most likely within the sphere of influence of the supermassive black hole.

Keywords: galaxy clusters; early-type galaxies; active galactic nuclei; giant molecular clouds; cooling flows; molecular gas
Damping of Slow Surface Kink Modes in Solar Photospheric Waveguides Modeled by One-dimensional Inhomogeneities

Given the recent interest in magnetohydrodynamic (MHD) waves in pores and sunspot umbrae, we examine the damping of slow surface kink modes (SSKMs) by modeling solar photospheric waveguides with a cylindrical inhomogeneity comprising a uniform interior, a uniform exterior, and a continuous transition layer (TL) in between. Performing an eigenmode analysis in linear, resistive, gravity-free MHD, our approach is idealized in that, among other things, our equilibrium is structured only in the radial direction. We can nonetheless address two damping mechanisms simultaneously, one being the ohmic resistivity and the other being the resonant absorption of SSKMs in the cusp and Alfvén continua. We find that the relative importance of the two mechanisms depends sensitively on the magnetic Reynolds number (Rm). Resonant absorption is the sole damping mechanism for realistically large values of Rm, and the cusp resonance in general dominates the Alfvén one unless the axial wavenumbers are at the lower end of the observationally relevant range. We also find that the thin-boundary approximation holds only when the TL-width-to-radius ratios are much smaller than nominally expected. The ohmic resistivity is far more important for realistically small Rm. Even in this case, SSKMs are only marginally damped, with damping-time-to-period ratios reaching ∼10 in the parameter range we examine.

Keywords: magnetohydrodynamics; solar photosphere; sunspots
Evolution of Circumstellar Disks around T Tauri Stars as a Function of Stellar Age

We analyzed the distribution of surface gravities, $\mathrm{log}\,g$ , of a sample of classical T Tauri stars in Taurus to examine the relationship between stellar ages and circumstellar disk evolution. This is critical to understanding the timescales for planet formation. Given the uncertainties in $\mathrm{log}\,g$ , we find no distinction between the ages of stars with and without disks beyond that identified previously. This approach, while avoiding the contamination that plagues young star luminosity measurements, will require precisions in $\mathrm{log}\,g$ of 0.05 dex or better to be effective.

Keywords: pre-main sequence stars; early stellar evolution
High-energy Radiation and Ion Acceleration in Three-dimensional Relativistic Magnetic Reconnection with Strong Synchrotron Cooling

We present the results of 3D particle-in-cell simulations that explore relativistic magnetic reconnection in pair plasma with strong synchrotron cooling and a small mass fraction of nonradiating ions. Our results demonstrate that the structure of the current sheet is highly sensitive to the dynamic efficiency of radiative cooling. Specifically, stronger cooling leads to more significant compression of the plasma and magnetic field within the plasmoids. We demonstrate that ions can be efficiently accelerated to energies exceeding the plasma magnetization parameter, ≫σ, and form a hard power-law energy distribution, f i ∝ γ -1. This conclusion implies a highly efficient proton acceleration in the magnetospheres of young pulsars. Conversely, the energies of pairs are limited to either σ in the strong cooling regime or the radiation burnoff limit, γ syn, when cooling is weak. We find that the high-energy radiation from pairs above the synchrotron burnoff limit, ɛ c ≈ 16 MeV, is only efficiently produced in the strong cooling regime, γ syn < σ. In this regime, we find that the spectral cutoff scales as ɛ cut ≈ ɛ c (σ/γ syn) and the highest energy photons are beamed along the direction of the upstream magnetic field, consistent with the phenomenological models of gamma-ray emission from young pulsars. Furthermore, our results place constraints on the reconnection-driven models of gamma-ray flares in the Crab Nebula.

Keywords: compact radiation sources; plasma astrophysics; high energy astrophysics
Morphological Star-Galaxy Separation

We discuss the statistical foundations of morphological star-galaxy separation. We show that many of the star-galaxy separation metrics in common use today (e.g., by Sloan Digital Sky Survey or SExtractor) are closely related both to each other, and to the model odds ratio derived in a Bayesian framework by Sebok. While the scaling of these algorithms with the noise properties of the sources varies, these differences do not strongly differentiate their performance. We construct a model of the performance of a star-galaxy separator in a realistic survey to understand the impact of observational signal-to-noise ratio (S/N) (or equivalently, 5σ limiting depth) and seeing on classification performance. The model quantitatively demonstrates that, assuming realistic densities and angular sizes of stars and galaxies, 10% worse seeing can be compensated for by approximately 0.4 mag deeper data to achieve the same star-galaxy classification performance. We discuss how to probabilistically combine multiple measurements, either of the same type (e.g., subsequent exposures), or differing types (e.g., multiple bandpasses), or differing methodologies (e.g., morphological and color-based classification). These methods are increasingly important for observations at faint magnitudes, where the rapidly rising number density of small galaxies makes star-galaxy classification a challenging problem. However, because of the significant role that the S/N plays in resolving small galaxies, surveys with large-aperture telescopes, such as LSST, will continue to see improving star-galaxy separation as they push to these fainter magnitudes.

Keywords: observational astronomy; ccd observation; astronomical methods
Deciphering Faint Gyrosynchrotron Emission from a Coronal Mass Ejection Using Spectropolarimetric Radio Imaging

Measurements of the plasma parameters of coronal mass ejections (CMEs), particularly the magnetic field and nonthermal electron population entrained in the CME plasma, are crucial to understand their propagation, evolution, and geo-effectiveness. Spectral modeling of gyrosynchrotron (GS) emission from CME plasma has been regarded as one of the most promising remote-sensing techniques for estimating spatially resolved CME plasma parameters. Imaging the very low flux density CME GS emission in close proximity to the Sun with orders of magnitude higher flux density has, however, proven to be rather challenging. This challenge has only recently been met using the high dynamic range imaging capability of the Murchison Widefield Array (MWA). Although routine detection of GS is now within reach, the challenge has shifted to constraining the large number of free parameters in GS models, a few of which are degenerate, using the limited number of spectral points at which the observations are typically available. These degeneracies can be broken using polarimetric imaging. For the first time, we demonstrate this using our recently developed capability of high-fidelity polarimetric imaging on the data from the MWA. We show that spectropolarimetric imaging, even when only sensitive upper limits on circularly polarization flux density are available, is not only able to break the degeneracies but also yields tighter constraints on the plasma parameters of key interest than possible with total intensity spectroscopic imaging alone.

Keywords: solar physics; solar coronal mass ejections; solar radio emission; solar magnetic fields; space weather