adsabs/SciX_UAT_keywords huggingface dataset:
Toward Precise Galaxy Evolution: A Comparison between Spectral Indices of z 1 Galaxies in the IllustrisTNG Simulation and the LEGA-C Survey

We present the first comparison of observed stellar continuum spectra of high-redshift galaxies and mock galaxy spectra generated from hydrodynamical simulations. The mock spectra are produced from the IllustrisTNG TNG100 simulation combined with stellar population models and take into account dust attenuation and realistic observational effects (aperture effects and noise). We compare the simulated Dn4000 and EW(Hδ) of galaxies with $10.5\leqslant \mathrm{log}({M}_{* }/{M}_{\odot })\leqslant 11.5$ at 0.6 ≤ z ≤ 1.0 to the observed distributions from the LEGA-C survey. TNG100 globally reproduces the observed distributions of spectral indices, implying that the age distribution of galaxies in TNG100 is generally realistic. Yet there are small but significant differences. For old galaxies, TNG100 shows small Dn4000 when compared to LEGA-C, while LEGA-C galaxies have larger EW(Hδ) at fixed Dn4000 . There are several possible explanations: (1) LEGA-C galaxies have overall older ages combined with small contributions (a few percent in mass) from younger (<1 Gyr) stars, while TNG100 galaxies may not have such young subpopulations; (2) the spectral mismatch could be due to systematic uncertainties in the stellar population models used to convert stellar ages and metallicities to observables. In conclusion, the latest cosmological galaxy-formation simulations broadly reproduce the global age distribution of galaxies at z ~ 1 and, at the same time, the high quality of the latest observed and simulated data sets help constrain stellar population synthesis models as well as the physical models underlying the simulations.

Keywords: galaxy ages; magnetohydrodynamical simulations; galaxy evolution; spectral index; galaxies; surveys; galaxy spectroscopy
Exploring the Emission Mechanisms of Mrk 180 with Long-term X-Ray and γ-Ray Data

Markarian (Mrk) 180 is a BL Lacertae object located at a redshift of 0.045 and is a potential candidate for high-energy cosmic-ray acceleration. We have analyzed the Fermi Large Area Telescope (Fermi-LAT) γ-ray data of Mrk 180 collected over a period of 12.8 yr and found no significant enhancement in the flux from the long-term γ-ray light curve. We have also analyzed Swift X-ray, ultraviolet, and optical, and X-ray Multi-Mirror Mission (XMM-Newton) data to construct the multiwavelength spectral energy distribution (SED). The SED has been modeled with one-zone pure leptonic and lepto-hadronic scenarios to explain the underlying physics of multiwavelength emission. The pure leptonic model and the two lepto-hadronic models, viz., (i) line-of-sight interactions of ultrahigh-energy cosmic rays (UHECRs; E ≳ 1017 eV) with the cosmic background radiation and (ii) the interactions of relativistic protons with the cold protons in the jet, have been compared in our work. Moreover, an earlier study has associated Mrk 180 with the Telescope Array (TA) hotspot of UHECRs at E > 57 EeV. This speculation motivates us to check whether ultrahigh-energy protons and iron nuclei can reach the Earth from Mrk 180. After comparing the results of our simulation with the current observational data, we find that Mrk 180 is unlikely to be a source of the UHECR events contributing to the TA hotspot for conservative strengths of extragalactic magnetic fields.

Keywords: high energy astrophysics; gamma-ray astronomy; active galactic nuclei; blazars; cosmic ray sources
Negligible Effects of Baryons on the Angular Momentum Scaling Relations of Galactic Dark Matter Halos

In cosmological simulations without baryons, the relation between the specific angular momentum j h and mass M h of galactic dark matter halos has the well-established form ${j}_{{\rm{h}}}\propto {M}_{{\rm{h}}}^{2/3}$ . This is invariably adopted as the starting point in efforts to understand the analogous relation between the specific angular momentum j * and mass M * of the stellar parts of galaxies, which are often re-expressed relative to the corresponding halo properties through the retention fractions f j = j */j h and f M = M */M h. An important caveat here is that the adopted ${j}_{{\rm{h}}}\propto {M}_{{\rm{h}}}^{2/3}$ relation could, in principle, be modified by the gravitational back-reaction of baryons on dark matter (DM). We have tested for this possibility by comparing the j h-M h relations in the IllustrisTNG100 and TNG50 simulations that include baryons (full-physics runs) with their counterparts that do not (DM-only runs). In all cases, we find scaling relations of the form ${j}_{{\rm{h}}}\propto {M}_{{\rm{h}}}^{\alpha }$ , with α ≈ 2/3 over the ranges of mass and redshift studied here: M h ≥ 1010 M ⊙ and 0 ≤ z ≤ 2. The values of α are virtually identical in the full-physics and DM-only runs at the same redshift. The only detectable effect of baryons on the j h-M h relation is a slightly higher normalization, by 12%-15% at z = 0 and by 5% at z = 2. This implies that existing estimates of f j based on DM-only simulations should be adjusted downward by similar amounts. Finally, we discuss briefly some implications of this work for studies of galaxy formation.

Keywords: galaxy formation; galaxy kinematics; galaxy dark matter halos; hydrodynamical simulations; scaling relations
Gamma-Ray Burst Pulses and Lateral Jet Motion

We propose that gamma-ray burst (GRB) pulses are produced when highly relativistic jets sweep across an observer's line of sight. We hypothesize that axisymmetric jet profiles, coupled with special relativistic effects, produce the time-reversed properties of GRB pulses. Curvature resulting from rapid jet expansion is responsible for much of the observed pulse asymmetry and hard-to-soft evolution. The relative obliqueness with which the jet crosses the line of sight explains the known GRB pulse morphological types. We explore two scenarios: one in which a rigid/semirigid jet moves laterally and another in which a ballistic jet sprays material from a laterally moving nozzle. The ballistic jet model is favored based upon its consistency with standard emission mechanisms.

Keywords: gamma-ray bursts; light curves; relativistic jets; special relativity
Torsional Alfvén Wave Cascade and Shocks Evolving in Solar Jets

The aim of this study is to model the nature of nonlinear torsional magnetohydrodynamic waves propagating in solar jets as they are elevated to the outer solar atmosphere. The contribution of sequential processes to the transfer of energy is taken under consideration: the nonlinear cascade and shock formation. Thus a straight magnetic cylinder embedded in a plasma with an initial magnetic field and parallel flow to the cylinder axis is implemented. To resemble a jet where the oscillation wavelength highly exceeds the radius, the second-order thin flux tube approximation proves adequate. A Cohen-Kulsrud type equation is presented, and its solution highly depends on the parameter presented in this study, which itself is constituted of various environmental and equilibrium conditions that affect the perturbations of the variables as well as the nonlinear forces connected to Alfvén wave propagation. The shock formation time of torsional waves is inversely proportional to the density contrast of the jet, while the efficiency of energy transfer to shorter scales is directly proportional to the density contrast. While the parallel flow with a shear at the boundary expedites shock formation, its efficiency regarding energy transfer is dramatically enhanced by the plasma-β, significantly contributing to coronal heating. The observational and seismological aspect of the present study is that faster jets are less probable for observations at higher altitudes, as they experience energy transfer mostly at the base of the corona, while slow speed jets may be observed at higher altitudes contributing to solar wind acceleration.

Keywords: the sun; alfven waves; magnetohydrodynamics; shocks
Mapping the Growth of Supermassive Black Holes as a Function of Galaxy Stellar Mass and Redshift

The growth of supermassive black holes is strongly linked to their galaxies. It has been shown that the population mean black hole accretion rate ( $\overline{\mathrm{BHAR}}$ ) primarily correlates with the galaxy stellar mass (M ⋆) and redshift for the general galaxy population. This work aims to provide the best measurements of $\overline{\mathrm{BHAR}}$ as a function of M ⋆ and redshift over ranges of 109.5 < M ⋆ < 1012 M ⊙ and z < 4. We compile an unprecedentedly large sample with 8000 active galactic nuclei (AGNs) and 1.3 million normal galaxies from nine high-quality survey fields following a wedding cake design. We further develop a semiparametric Bayesian method that can reasonably estimate $\overline{\mathrm{BHAR}}$ and the corresponding uncertainties, even for sparsely populated regions in the parameter space. $\overline{\mathrm{BHAR}}$ is constrained by X-ray surveys sampling the AGN accretion power and UV-to-infrared multiwavelength surveys sampling the galaxy population. Our results can independently predict the X-ray luminosity function (XLF) from the galaxy stellar mass function (SMF), and the prediction is consistent with the observed XLF. We also try adding external constraints from the observed SMF and XLF. We further measure $\overline{\mathrm{BHAR}}$ for star-forming and quiescent galaxies and show that star-forming $\overline{\mathrm{BHAR}}$ is generally larger than or at least comparable to the quiescent $\overline{\mathrm{BHAR}}$ .

Keywords: supermassive black holes; x-ray active galactic nuclei; galaxies
VLBA Reveals the Absence of a Compact Radio Core in the Radio-intermediate Quasar J2242+0334 at z = 5.9

High-resolution imaging is crucial for exploring the origin and mechanism of radio emission in quasars, especially at high redshifts. We present 1.5 GHz Very Long Baseline Array (VLBA) images of the radio continuum emission from the radio-intermediate quasar (RIQ) J2242+0334 at z = 5.9. This object was previously detected at both 1.5 GHz and 3 GHz with the Karl G. Jansky Very Large Array (VLA) as a point source. However, there is no clear detection in the VLBA images at both the full resolution of 10.7 mas × 4.5 mas (61.7 pc × 26.0 pc) and a tapered resolution of 26 mas × 21 mas (150 pc × 121 pc). This suggests that the radio emission from the quasar is diffuse on milliarcsecond scales with surface brightness fainter than the 3σ detection limit of 40.5 μJy beam-1 in the full-resolution image. The radio emission in the RIQ J2242+0334 is likely to be wind-like (i.e., diffuse) rather than in the form of collimated jets. This is different from the previous radio detections of the most luminous quasars at z ~ 6 that are usually dominated by compact, high brightness temperature radio sources. Meanwhile, compared with RIQs at low redshifts, the case of J2242+0334 suggests that not all RIQs are beamed radio-quiet quasars. This optically faint RIQ provides an important and unique example to investigate the radio activity in the less powerful active galactic nuclei at the earliest cosmic epoch.

Keywords: radio continuum emission; early universe; quasars
Multiwavelength Observations of MWC 297: Constraints on Disk Inclination and Mass Outflow

MWC 297 is a young, early-type star driving an ionized outflow and surrounded by warm, entrained dust. Previous analyses of near- and mid-IR interferometric images suggest that the emission at these wavelengths arises from a compact accretion disk with a moderate (i < 40°) inclination. We have obtained 5-40 μm images of MWC 297 with FORCAST on SOFIA, as well as near-infrared spectra acquired with SpeX on the IRTF and radio data obtained with the VLA and BIMA, and supplemented these with archival data from Herschel/PACS and SPIRE. The FORCAST images, combined with the VLA data, indicate that the outflow lobes are aligned nearly north-south and are well separated. Simple geometrical modeling of the FORCAST images suggests that the disk driving the outflow has an inclination of 55° ± 5°, in disagreement with the results of the interferometric analyses. Analysis of the SpeX data, with a wind model, suggests the mass-loss rate is on the order of $6.0{\pm }_{1.7}^{3.7}\times {10}^{-7}{M}_{\odot }\,{\mathrm{yr}}^{-1}$ and the extinction to the source is ${A}_{V}\sim 8.1{\pm }_{1.5}^{2.5}$ mag. We have combined our data with values from the literature to generate the spectral energy distribution of the source from 0.35 μm to 6 cm and estimate the total luminosity. We find the total luminosity to be about 7900 L ⊙, if we include emission from an extended region around the star, only slightly below that expected for a B1.5V star. The reddening must be produced by dust along the line of sight, but distant from the star.

Keywords: stellar accretion disks; herbig ae/be stars; young stellar objects; pre-main sequence stars
Enhanced Energy Transfer Rate in Solar Wind Turbulence Observed near the Sun from Parker Solar Probe

Direct evidence of an inertial-range turbulent energy cascade has been provided by spacecraft observations in heliospheric plasmas. In the solar wind, the average value of the derived heating rate near 1 au is $\sim {10}^{3}\,{\rm{J}}\,{\mathrm{kg}}^{-1}\,{{\rm{s}}}^{-1}$ , an amount sufficient to account for observed departures from adiabatic expansion. Parker Solar Probe, even during its first solar encounter, offers the first opportunity to compute, in a similar fashion, a fluid-scale energy decay rate, much closer to the solar corona than any prior in situ observations. Using the Politano-Pouquet third-order law and the von Kármán decay law, we estimate the fluid-range energy transfer rate in the inner heliosphere, at heliocentric distance R ranging from 54 R⊙ (0.25 au) to 36 R⊙ (0.17 au). The energy transfer rate obtained near the first perihelion is about 100 times higher than the average value at 1 au, which is in agreement with estimates based on a heliospheric turbulence transport model. This dramatic increase in the heating rate is unprecedented in previous solar wind observations, including those from Helios, and the values are close to those obtained in the shocked plasma inside the terrestrial magnetosheath.

Keywords: interplanetary shocks; solar wind; magnetohydrodynamics
Submerged Sources of Transient Acoustic Emission from Solar Flares

We report the discovery of ultra-impulsive acoustic emission from a solar flare, emission with a seismic signature that indicates submersion of its source approximately a Mm beneath the photosphere of the active region that hosted the flare. Just over two decades ago V. V. Zharkova and A. G. Kosovichev discovered the first acoustic transient released into the Sun's interior by a solar flare. These acoustic waves, refracted back upward to the solar surface after their release, make conspicuous Doppler ripples spreading outward from the flaring region that tell us a lot about their sources. The mechanism by which these transients are driven has stubbornly eluded our understanding. Some of the source regions, for example, are devoid of secondary Doppler, magnetic, or thermal disturbances in the outer atmosphere of the source regions that would signify the driving agent of an intense seismic transient in the outer atmosphere. In this study, we have applied helioseismic holography, a diagnostic based upon standard wave optics, to reconstruct a 3D image of the sources of acoustic waves emanating from the M9.3-class flare of 2011 July 30. These images contain a source component that is submerged a full Mm beneath the active-region photosphere. The signature of acoustic sources this deep in the solar interior opens new considerations into the physics that must be involved in transient acoustic emission from flares—and possibly of flare physics at large. We develop analogies to seismicity remotely triggered by tremors from distant earthquakes, and consider prospects of new insight into the architecture of magnetic flux beneath flaring active regions.

Keywords: solar physics; helioseismology; solar flares
X-Ray Unveiling Events in a z ≈ 1.6 Active Galactic Nucleus in the 7 Ms Chandra Deep Field-South

We investigate the extreme X-ray variability of a z = 1.608 active galactic nucleus in the 7 Ms Chandra Deep Field-South (XID 403), which showed two significant X-ray brightening events. In the first event, XID 403 brightened by a factor of >2.5 in ≲6.1 rest-frame days in the observed-frame 0.5-5 keV band. The event lasted for ≈5.0-7.3 days, and then XID 403 dimmed by a factor of >6.0 in ≲6.1 days. After ≈1.1-2.5 yr in the rest frame (including long observational gaps), it brightened again, with the 0.5-5 keV flux increasing by a factor of >12.6. The second event lasted over 251 days, and the source remained bright until the end of the 7 Ms exposure. The spectrum is a steep power law (photon index Γ = 2.8 ± 0.3) without obscuration during the second outburst, and the rest-frame 2-10 keV luminosity reaches ${1.5}_{-0.5}^{+0.8}\times {10}^{43}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ ; there is no significant spectral evolution within this epoch. The infrared-to-UV spectral energy distribution of XID 403 is dominated by the host galaxy. There is no significant optical/UV variability and R-band (rest-frame ≈2500 Å) brightening contemporaneous with the X-ray brightening. The extreme X-ray variability is likely due to two X-ray unveiling events, where the line of sight to the corona is no longer shielded by high-density gas clumps in a small-scale dust-free absorber. XID 403 is probably a high-redshift analog of local narrow-line Seyfert 1 galaxies, and the X-ray absorber is a powerful accretion disk wind. On the other hand, we cannot exclude the possibility that XID 403 is an unusual candidate for tidal disruption events.

Keywords: x-ray active galactic nuclei; active galactic nuclei; seyfert galaxies; surveys
A Unified Model of Solar Prominence Formation

Several mechanisms have been proposed to account for the formation of solar prominences or filaments, among which direct injection and evaporation-condensation models are the two most popular ones. In the direct injection model, cold plasma is ejected from the chromosphere into the corona along magnetic field lines; in the evaporation-condensation model, the cold chromospheric plasma is heated to over a million degrees and is evaporated into the corona, where the accumulated plasma finally reaches thermal instability or nonequilibrium so as to condensate to cold prominences. In this paper, we try to unify the two mechanisms: The essence of filament formation is the localized heating in the chromosphere. If the heating happens in the lower chromosphere, the enhanced gas pressure pushes the cold plasma in the upper chromosphere to move up to the corona, such a process is manifested as the direct injection model. If the heating happens in the upper chromosphere, the local plasma is heated to 1-2 million degrees, and is evaporated into the corona. Later, the plasma condensates to form a prominence. Such a process is manifested as the evaporation-condensation model. With radiative hydrodynamic simulations we confirmed that the two widely accepted formation mechanisms of solar prominences can really be unified in such a single framework. A particular case is also found where both injection and evaporation-condensation processes occur together.

Keywords: solar prominences; solar filaments; hydrodynamical simulations; solar chromosphere
Is the Black-widow Pulsar PSR J1555-2908 in a Hierarchical Triple System?

The 559 Hz black-widow pulsar PSR J1555-2908, originally discovered in radio, is also a bright gamma-ray pulsar. Timing its pulsations using 12 yr of Fermi-Large Area Telescope gamma-ray data reveals long-term variations in its spin frequency that are much larger than is observed from other millisecond pulsars. While this variability in the pulsar rotation rate could be intrinsic "timing noise," here we consider an alternative explanation: the variations arise from the presence of a very-low-mass third object in a wide multiyear orbit around the neutron star and its low-mass companion. With current data, this hierarchical-triple-system model describes the pulsar's rotation slightly more accurately than the best-fitting timing noise model. Future observations will show if this alternative explanation is correct.

Keywords: gamma-ray sources; millisecond pulsars; pulsar planets; pulsar timing method
Deep Learning for Line Intensity Mapping Observations: Information Extraction from Noisy Maps

Line intensity mapping (LIM) is a promising observational method to probe large-scale fluctuations of line emission from distant galaxies. Data from wide-field LIM observations allow us to study the large-scale structure of the universe as well as galaxy populations and their evolution. A serious problem with LIM is contamination by foreground/background sources and various noise contributions. We develop conditional generative adversarial networks (cGANs) that extract designated signals and information from noisy maps. We train the cGANs using 30,000 mock observation maps with assuming a Gaussian noise matched to the expected noise level of NASA's SPHEREx mission. The trained cGANs successfully reconstruct Hα emission from galaxies at a target redshift from observed, noisy intensity maps. Intensity peaks with heights greater than 3.5σnoise are located with 60% precision. The one-point probability distribution and the power spectrum are accurately recovered even in the noise-dominated regime. However, the overall reconstruction performance depends on the pixel size and on the survey volume assumed for the training data. It is necessary to generate training mock data with a sufficiently large volume in order to reconstruct the intensity power spectrum at large angular scales. The suitably trained cGANs perform robustly against variations of the galaxy line emission model. Our deep-learning approach can be readily applied to observational data with line confusion and with noise.

Keywords: observational cosmology; astronomical methods; large-scale structure of the universe
A Panchromatic Study of Massive Stars in the Extremely Metal-poor Local Group Dwarf Galaxy Leo A

We characterize massive stars (M > 8 M ⊙) in the nearby (D ∼ 0.8 Mpc) extremely metal-poor (Z ∼ 5% Z ⊙) galaxy Leo A using Hubble Space Telescope ultraviolet (UV), optical, and near-infrared (NIR) imaging along with Keck/Low-Resolution Imaging Spectrograph and MMT/Binospec optical spectroscopy for 18 main-sequence OB stars. We find that: (a) 12 of our 18 stars show emission lines, despite not being associated with an H II region, suggestive of stellar activity (e.g., mass loss, accretion, binary star interaction), which is consistent with previous predictions of enhanced activity at low metallicity; (b) six are Be stars, which are the first to be spectroscopically studied at such low metallicity-these Be stars have unusual panchromatic SEDs; (c) for stars well fit by the TLUSTY nonlocal thermodynamic equilibrium models, the photometric and spectroscopic values of log(Teff) and log(g) agree to within ∼0.01 dex and ∼0.18 dex, respectively, indicating that near-UV/optical/NIR imaging can be used to reliably characterize massive (M ∼8-30 M ⊙) main-sequence star properties relative to optical spectroscopy; (d) the properties of the most-massive stars in H II regions are consistent with constraints from previous nebular emission line studies; and (e) 13 stars with M > 8M ⊙ are >40 pc from a known star cluster or H II region. Our sample comprises ∼50% of all known massive stars at Z ≲ 10% Z ⊙with derived stellar parameters, high-quality optical spectra, and panchromatic photometry. *This paper includes data gathered with the 10 m Keck Telescopes located at W. M. Keck Observatory, Hawaii and with the 6.5 m Multiple Mirror Telescope (MMT) located at Mt. Hopkins, Arizona.

Keywords: massive stars; metallicity; early-type stars