adsabs/SciX_UAT_keywords huggingface dataset:
The Star Formation History in Local Group Galaxies. I. Ten Dwarf Galaxies

The star formation histories (SFHs) of galaxies provide valuable insights into galaxy evolution and stellar physics. Understanding the SFHs enables the study of chemical enrichment of galaxies, star formation triggered by interactions, and the behavior of various stellar populations. This work investigates the SFHs of ten dwarf galaxies in the Local Group (LG), which spans a wide range of types, masses, luminosities, and metallicities. The analysis is based on our new sample of the member stars in the LG after removing foreground dwarf stars by using information from the near-infrared color–color diagram and Gaia astrometry. The sample includes the most complete and pure red supergiants and asymptotic giant branch stars to gain valuable insights into the recent SFHs of the galaxies. A fitting method based on the color–magnitude diagram (CMD) is introduced to measure the SFH. The Padova isochrones are used to generate initial model CMDs, accounting for photometric errors and completeness through star-field simulations to match the completeness and error distributions of the observed CMDs. Subsequently, the SFHs, distance modulus, and metallicity of the ten dwarf galaxies are determined by fitting the CMDs. The results indicate that the star formation rates of dwarf irregulars show a gradual increase, while those of dwarf ellipticals exhibit a gradual decrease from the past to the present. Furthermore, this work shows that the star formation activity in dwarf ellipticals persisted up to 30 Myr ago. A significant increasing feature in the SFH of NGC 6822 reveals star formation activity triggered by an interaction event.

Keywords: massive stars; red supergiant stars; local group; dwarf galaxies; stellar evolutionary models; star formation
JWST NIRSpec Observations of Supernova 1987A-From the Inner Ejecta to the Reverse Shock

We present initial results from JWST NIRSpec integral field unit observations of the nearby supernova SN 1987A. The observations provide the first spatially resolved spectroscopy of the ejecta and equatorial ring (ER) over the 1-5 μm range. We construct 3D emissivity maps of the [Fe I] 1.443 μm line from the inner ejecta and the He I 1.083 μm line from the reverse shock (RS), where the former probes the explosion geometry and the latter traces the structure of the circumstellar medium. We also present a model for the integrated spectrum of the ejecta. The [Fe I] 3D map reveals a highly asymmetric morphology resembling a broken dipole, dominated by two large clumps with velocities of ~2300 km s-1. We also find evidence that the Fe-rich inner ejecta have started to interact with the RS. The RS surface traced by the He I line extends from just inside the ER to higher latitudes on both sides of the ER with a half-opening angle ~45°, forming a bubble-like structure. The spectral model for the ejecta allows us to identify the many emission lines, including numerous H2 lines. We find that the H2 is most likely excited by far-UV emission, while the metal-line ratios are consistent with a combination of collisional excitation and recombination in the low-temperature ejecta. We also find several high-ionization coronal lines from the ER, requiring a temperature ≳2 × 106 K.

Keywords: supernova remnants; core-collapse supernovae
Dynamical Mass Estimates of the β Pictoris Planetary System through Gaussian Process Stellar Activity Modeling

Nearly 15 yr of radial velocity (RV) monitoring and direct imaging enabled the detection of two giant planets orbiting the young, nearby star β Pictoris. The δ Scuti pulsations of the star, which overwhelm planetary signals, need to be carefully suppressed. In this work, we independently revisit the analysis of the RV data following a different approach than available in the literature to model the activity of the star. We show that a Gaussian process (GP) with a stochastically driven damped harmonic oscillator kernel can model the δ Scuti pulsations. It provides similar results to parametric models but with a simpler framework, using only three hyperparameters. It also enables us to model poorly sampled RV data that were excluded from previous analyses, hence extending the RV baseline by nearly five years. Altogether, the orbit and mass of both planets can be constrained from RV only, which was not possible with the parametric modeling. To characterize the system more accurately, we also perform a joint fit of all available relative astrometry and RV data. Our orbital solutions for $\beta \ \mathrm{Pic}$ b favor a low eccentricity of ${0.029}_{-0.024}^{+0.061}$ and a relatively short period of ${21.1}_{-0.8}^{+2.0}$ yr. The orbit of $\beta \ \mathrm{Pic}$ c is eccentric with ${0.206}_{-0.063}^{+0.074}$ with a period of 3.36 ± 0.03 yr. We find model-independent masses of 11.7 ± 1.4 and 8.5 ± 0.5 ${M}_{\mathrm{Jup}}$ for $\beta \ \mathrm{Pic}$ b and c, respectively, assuming coplanarity. The mass of $\beta \ \mathrm{Pic}$ b is consistent with the hottest start evolutionary models, at an age of 25 ± 3 Myr. A direct detection of $\beta \ \mathrm{Pic}$ c would provide a second calibration measurement in a coeval system.

Keywords: exoplanets; radial velocity; gaussian processes regression; astrometry; orbit determination; delta scuti variable stars
Stars Lensed by the Supermassive Black Hole in the Center of the Milky Way: Predictions for ELT, TMT, GMT, and JWST

Gravitational lensing is an important prediction of general relativity, providing both its test and a tool to detect faint but amplified sources and to measure masses of lenses. For some applications, (e.g., testing the theory), a point source lensed by a point-like lens would be more advantageous. However, until now only one gravitationally lensed star has been resolved. Future telescopes will resolve very small lensing signatures for stars orbiting the supermassive black hole (SMBH) in the center of the Milky Way. The lensing signatures, however, should be easier to detect for background stars. We predict that the Extremely Large Telescope (ELT), Thirty Meter Telescope (TMT), and Giant Magellan Telescope (GMT) will resolve the lensed images of around 100 (60) stars in the disk and 30 (20) stars in the bulge in the background of the SMBH, down to 28 (27) mag (Vega) limits at K-band, requiring 5 (1) hr of integration. In order to detect several such stars one needs the limit of at least 24 mag. With decade-long monitoring, one can also detect the rotation of the lensed images. The detection of elongated images will not be possible, because this would require a nearly perfect source-lens alignment. The James Webb Space Telescope (JWST) will likely be limited by the confusion caused by stars near the Galactic center. The detection of such lensed images will provide a very clean test of general relativity, when combined with the SMBH mass measurement from orbital motions of stars, and accurate measurements of the SMBH properties, because both the source and the lens can be considered point-like.

Keywords: optical telescopes; galactic center; supermassive black holes; strong gravitational lensing
Mitigating Shear-dependent Object Detection Biases with Metacalibration

METACALIBRATION is a new technique for measuring weak gravitational lensing shear that is unbiased for isolated galaxy images. In this work we test METACALIBRATION with overlapping, or "blended" galaxy images. Using standard METACALIBRATION, we find a few percent shear measurement bias for galaxy densities relevant for current surveys, and that this bias increases with increasing galaxy number density. We show that this bias is not due to blending itself, but rather to shear-dependent object detection. If object detection is shear-independent, no deblending of images is needed, in principle. We demonstrate that detection biases are accurately removed when including object detection in the METACALIBRATION process, a technique we call METADETECTION. This process involves applying an artificial shear to images of small regions of sky and performing detection on the sheared images, as well as measurements that are used to calculate a shear response. We demonstrate that the method can accurately recover weak shear signals even in highly blended scenes. In the METACALIBRATION process, the space between objects is sheared coherently, which does not perfectly match the real universe in which some, but not all, galaxy images are sheared coherently. We find that even for the worst case scenario, in which the space between objects is completely unsheared, the resulting shear bias is at most a few tenths of a percent for future surveys. We discuss additional technical challenges that must be met in order to implement METADETECTION for real surveys.

Keywords: weak gravitational lensing
The Cosmic Merger Rate Density Evolution of Compact Binaries Formed in Young Star Clusters and in Isolated Binaries

Next generation ground-based gravitational-wave detectors will observe binary black hole (BBH) mergers up to redshift $z\gtrsim 10$ , probing the evolution of compact binary (CB) mergers across cosmic time. Here, we present a new data-driven model to estimate the cosmic merger rate density (MRD) evolution of CBs, by coupling catalogs of CB mergers with observational constraints on the cosmic star formation rate (SFR) density and on the metallicity evolution of the universe. We adopt catalogs of CB mergers derived from recent N-body and population-synthesis simulations, to describe the MRD of CBs formed in young star clusters (hereafter, dynamical CBs) and in the field (hereafter, isolated CBs). The local MRD of dynamical BBHs is ${{ \mathcal R }}_{\mathrm{BBH}}={64}_{-20}^{+34}$ Gpc-3 yr-1, consistent with the 90% credible interval from the first and second observing runs (O1 and O2) of the LIGO-Virgo collaboration, and with the local MRD of isolated BBHs ( ${{ \mathcal R }}_{\mathrm{BBH}}={50}_{-37}^{+71}$ Gpc-3 yr-1). The local MRD of dynamical and isolated black hole-neutron star binaries is ${{ \mathcal R }}_{\mathrm{BHNS}}={41}_{-23}^{+33}$ and ${49}_{-34}^{+48}$ Gpc-3 yr-1, respectively. Both values are consistent with the upper limit inferred from O1 and O2. Finally, the local MRD of dynamical binary neutron stars (BNSs, ${{ \mathcal R }}_{\mathrm{BNS}}={151}_{-38}^{+59}$ Gpc-3 yr-1) is a factor of two lower than the local MRD of isolated BNSs ( ${{ \mathcal R }}_{\mathrm{BNS}}={283}_{-75}^{+97}$ Gpc-3 yr-1). The MRD for all CB classes grows with redshift, reaching its maximum at $z\in [1.5,2.5]$ , and then decreases. This trend springs from the interplay between cosmic SFR, metallicity evolution, and delay time of binary compact objects.

Keywords: gravitational waves; astrophysical black holes; neutron stars; star formation; binary stars
Accurate Treatment of Comptonization in X-Ray Illuminated Accretion Disks

A large fraction of accreting black hole and neutron star systems present clear evidence of the reprocessing of X-rays in the atmosphere of an optically thick accretion disk. The main hallmarks of X-ray reflection include fluorescent K-shell emission lines from iron (∼6.4-6.9 keV), the absorption iron K-edge (∼7-9 keV), and a broad featureless component known as the Compton hump (∼20-40 keV). This Compton hump is produced as the result of the scattering of high-energy photons (E ≳ 10 keV) of the relatively colder electrons (Te ∼ 105-107 K) in the accretion disk, in combination with photoelectric absorption from iron. The treatment of this process in most current models of ionized X-ray reflection has been done using an approximated Gaussian redistribution kernel. This approach works sufficiently well up to ∼100 keV, but it becomes largely inaccurate at higher energies and at relativistic temperatures (Te ∼ 109 K). We present new calculations of X-ray reflection using a modified version of our code xillver, including an accurate solution for Compton scattering of the reflected unpolarized photons in the disk atmosphere. This solution takes into account quantum electrodynamic and relativistic effects allowing the correct treatment of high photon energies and electron temperatures. We show new reflection spectra computed with this model, and discuss the improvements achieved in reproducing the correct shape of the Compton hump, the discrepancies with previous calculations, and the expected impact of these new models in the interpretation of observational data.

Keywords: radiative transfer simulations; astronomical simulations; stellar accretion disks; accretion; black hole physics; atomic spectroscopy
The Colors of Bulges and Disks in the Core and Outskirts of Galaxy Clusters

The role of the environment on the formation of S0 galaxies is still not well understood, specifically in the outskirts of galaxy clusters. We study eight low-redshift clusters, analyzing galaxy members up to cluster-centric distances of ∼2.5 R200. We perform 2D photometric bulge-disk decomposition in the g, r, and i bands from which we identify 469 double-component galaxies. We separately analyze the colors of the bulges and disks and their dependence on the projected cluster-centric distance and local galaxy density. For our sample of cluster S0 galaxies, we find that bulges are redder than their surrounding disks, show a significant color-magnitude trend, and have colors that do not correlate with environment metrics. On the other hand, the disks associated with our cluster S0s become significantly bluer with increasing cluster-centric radius but show no evidence for a color-magnitude relation. The disk color-radius relation is mainly driven by galaxies in the cluster core at 0 ≤ R/R200 < 0.5. No significant difference is found for the disk colors of backsplash and infalling galaxies in the projected phase space (PPS). Beyond R200, the disk colors do not change with the local galaxy density, indicating that the colors of double-component galaxies are not affected by preprocessing. A significant color-density relation is observed for single-component disk-dominated galaxies beyond R200. We conclude that the formation of cluster S0 galaxies is primarily driven by cluster core processes acting on the disks, while evidence of preprocessing is found for single-component disk-dominated galaxies. We publicly release the data from the bulge-disk decomposition.

Keywords: galaxy clusters; galaxy evolution; galaxy structure; redshift surveys; galaxy colors
The Slipping Magnetic Reconnection and Damped Quasiperiodic Pulsations in a Circular Ribbon Flare

The study of circular ribbon (CR) flares is important to understand the three-dimensional magnetic reconnection in the solar atmosphere. We investigate the slipping brightenings and damped quasiperiodic pulsations in a CR flare by multiwavelength observations. During the flaring process, two extreme ultraviolet brightenings (SP1 and SP2) slip synchronously along the ribbon in a counterclockwise direction. The ribbon and fans between them show synchronous enhancement with the microwave and hard X-ray (HXR) CR source. In the magnetohydrostatic extrapolation results and observations, the dome and outer spine display an evident counterclockwise twisting feature. We propose the slipping reconnection occurs between the fan and outer spine in the null point, which covers the region from SP1 to SP2. The fan of SP1 shows the strongest twist and produces the most efficient reconnection. The ribbon after SP1 becomes weak due to the destruction of the fan configuration. The fan of SP2 is in the front of the slipping motion, which initiates new reconnection and brightens the local ribbon. The twisting of the dome continuously promotes new reconnection in the null point, which brightens the ribbon in sequence to display a counterclockwise slipping feature. Thus, the twist of the dome may trigger and dominate the slipping reconnection, and the rotation of the central positive pole could be one possible cause of the twist. After the peak, the microwave and HXR emission shows damped oscillations at a period of 15 s. The collapse of the fan–spine structure may lead to the standing kink oscillations of the fan to modulate the reconnection and particle acceleration process.

Keywords: solar flares; solar magnetic reconnection; solar radio emission
Spectroscopic Fourth-order Coronagraph for the Characterization of Terrestrial Planets at Small Angular Separations from Host Stars

We propose a new approach for high-contrast imaging at the diffraction limit using segmented telescopes in a modest observation bandwidth. This concept, named "spectroscopic fourth-order coronagraphy," is based on a fourth-order coronagraph with a focal-plane mask that modulates the complex amplitude of the Airy disk along one direction. While coronagraphs applying the complex amplitude mask can achieve the theoretical limit performance for any arbitrary pupils, the focal-plane mask severely limits the bandwidth. Here, focusing on the fact that the focal-plane mask modulates the complex amplitude along one direction, we noticed that the mask can be optimized for each spectral element generated by a spectrograph. We combine the fourth-order coronagraph with two spectrographs to produce a stellar spectrum on the focal plane and reconstruct a white pupil on the Lyot stop. Based on the wave-front analysis of an optical design applying an Offner-type imaging spectrograph, we found that the achievable contrast of this concept is 10-10 at 1.2-1.5 times the diffraction limit over the wavelength range of 650-750 nm for the entrance pupil of the LUVOIR telescope. Thus, this coronagraph concept could bring new habitable planet candidates not only around G- and K-type stars beyond 20-30 pc but also around very nearby M-type stars. This approach potentially promotes the characterization of the atmospheres of nearby terrestrial planets with future on- and off-axis segmented large telescopes.

Keywords: infrared telescopes; space vehicle instruments; coronagraphic imaging; direct imaging; spectroscopy
Detection of Ionized Calcium in the Atmosphere of the Ultra-hot Jupiter KELT-9b

With a dayside temperature in excess of 4500 K, comparable to a mid-K-type star, KELT-9b is the hottest planet known. Its extreme temperature makes KELT-9b a particularly interesting test bed for investigating the nature and diversity of gas giant planets. We observed the transit of KELT-9b at high spectral resolution (R ∼ 94,600) with the CARMENES instrument on the Calar Alto 3.5 m telescope. Using these data, we detect for the first time ionized calcium (Ca II triplet) absorption in the atmosphere of KELT-9b; this is the second time that Ca II has been observed in a hot Jupiter. Our observations also reveal prominent Hα absorption, confirming the presence of an extended hydrogen envelope around KELT-9b. We compare our detections with an atmospheric model and find that all four lines form between atmospheric temperatures of 6100 and 8000 K and that the Ca II lines form at pressures between 50 and 100 nbar while the Hα line forms at a lower pressure (∼10 nbar), higher up in the atmosphere. The altitude that the core of Hα line forms is found to be ∼1.4 R p , well within the planetary Roche lobe (∼1.9 R p ). Therefore, rather than probing the escaping upper atmosphere directly, the Hα line and the other observed Balmer and metal lines serve as atmospheric thermometers enabling us to probe the planet’s temperature profile, thus the energy budget.

Keywords: exoplanet atmospheres; planetary atmospheres; extrasolar gaseous giant planets; exoplanets; hot jupiters; exoplanet atmospheric composition
Spectroscopic Follow-up of Two Star-forming Objects in the M101 Field

We present the spectra of two faint star-forming objects originally identified in our deep narrowband survey of the M101 Group. One is an isolated H II region near the M101 Group galaxy NGC 5474, and the other is projected close to the background galaxy NGC 5486. Both are spectroscopically confirmed to be physically associated with their nearby host. We estimate the oxygen abundances for each system using strong-line methods. For the source near NGC 5474, we use GALEX UV photometry to estimate an age of ~200 Myr and suggest a connection to the M101-NGC 5474 interaction. *Based on observations obtained with the Hobby-Eberly Telescope (HET), which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Ludwig-Maximillians-Universitaet Muenchen, and Georg-August Universitaet Goettingen.

Keywords: star forming regions; chemical abundances; spectroscopy
Flat-spectrum Radio Quasars and BL Lacs Dominate the Anisotropy of the Unresolved Gamma-Ray Background

We analyze the angular power spectrum (APS) of the unresolved gamma-ray background (UGRB) emission and combine it with the measured properties of the resolved gamma-ray sources of the Fermi-LAT 4FGL catalog. Our goals are to dissect the composition of the gamma-ray sky and to establish the relevance of different classes of source populations of active galactic nuclei in determining the observed size of the UGRB anisotropy, especially at low energies. We find that, under physical assumptions for the spectral energy distribution, i.e., by using the 4FGL catalog data as a prior, two populations are required to fit the APS data, namely flat-spectrum radio quasars at low energies and BL Lacs at higher energies. The inferred luminosity functions agree well with the extrapolation of the flat-spectrum radio quasar and BL Lac ones obtained from the 4FLG catalog. We use these luminosity functions to calculate the UGRB intensity from blazars, finding a contribution of 20% at 1 GeV and 30% above 10 GeV. Finally, bounds on an additional gamma-ray emission due to annihilating dark matter are also derived.

Keywords: gamma-ray sources; blazars; gamma-rays
The Assembly of Black Hole Mass and Luminosity Functions of High-redshift Quasars via Multiple Accretion Episodes

The early evolution of the quasar luminosity function (QLF) and black hole mass function (BHMF) encodes key information on the physics determining the radiative and accretion processes of supermassive black holes (BHs) in high-z quasars. Although the QLF shape has been constrained by recent observations, it remains challenging to develop a theoretical model that explains its redshift evolution associated with BH growth self-consistently. In this study, based on a semianalytical model for the BH formation and growth, we construct the QLF and BHMF of the early BH population that experiences multiple accretion bursts, in each of which a constant Eddington ratio is assigned following a Schechter distribution function. Our best-fit model to reproduce the observed QLF and BHMF at z ≃ 6 suggests that several episodes of moderate super-Eddington accretion occur and each of them lasts for τ ≃ 20-30 Myr. The average duty cycle in super-Eddington phases is ≃15% for massive BHs that reach ≳108 M ⊙ by z ≃ 6, which is nearly twice that of the entire population. We find that the observed Eddington ratio distribution function is skewed to a lognormal shape owing to detection limits of quasar surveys. The predicted redshift evolution of the QLF and BHMF suggests a rapid decay of their number and mass density in a cosmic volume toward z ≳ 6. These results will be unveiled by future deep and wide surveys with the James Webb Space Telescope, Roman Space Telescope, and Euclid.

Keywords: quasars; supermassive black holes