adsabs/SciX_UAT_keywords huggingface dataset:
Magellanic Mayhem: Metallicities and Motions

We assemble a catalog of Magellanic Cloud red giants from Data Release 2 of the Gaia mission and, utilizing machine-learning methods, obtain photometric metallicity estimates for them. In doing so, we are able to chemically map the entirety of the Magellanic System at once. Our maps reveal a plethora of substructure within our red giant sample, with the Large Magellanic Cloud (LMC) bar and spiral arm being readily apparent. We uncover a curious spiral-like feature in the southern portion of the LMC disk, hosting relatively metal-rich giants and likely a by-product of historic encounters with the Small Magellanic Cloud (SMC). Modeling the LMC as an inclined thin disk, we find a shallow metallicity gradient of -0.048 ± 0.001 dex kpc-1 out to ∼12° from the center of the dwarf. We see evidence that the SMC is disrupting, with its outer isodensity contours displaying the S-shape symptomatic of tidal stripping. On studying the proper motions of the SMC giants, we observe a population of them being violently dragged toward the larger Cloud. The perturbed stars predominantly lie in front of the SMC, and we interpret that they exist as a tidal tail of the dwarf, trailing in its motion and undergoing severe disruption from the LMC. We find the metallicity structure in the Magellanic Bridge region to be complex, with evidence for a composite nature in this stellar population, consisting of both LMC and SMC debris.

Keywords: galaxies; local group; large magellanic cloud; small magellanic cloud
A Candidate for the Least-massive Black Hole in the First 1.1 Billion Years of the Universe

We report a candidate of a low-luminosity active galactic nucleus (AGN) at z = 5 that was selected from the first near-infrared images of the JWST CEERS project. This source, named CEERS-AGN-z5-1 at absolute 1450 Å magnitude M 1450 = -19.5 ± 0.3, was found via a visual selection of compact sources from a catalog of Lyman break galaxies at z > 4, taking advantage of the superb spatial resolution of the JWST/NIRCam images. The 20 photometric data available from CFHT, Hubble Space Telescope, Spitzer, and JWST suggest that the continuum shape of this source is reminiscent of that for an unobscured AGN, and there is a clear color excess in the filters where the redshifted Hβ+[O III] and Hα are covered. The estimated line luminosity is L Hβ+[O III] = 1043.0 erg s-1 and L Hα = 1042.9 erg s-1 with the corresponding rest-frame equivalent width EWHβ+[O III] = 1100 Å and EWHα = 1600 Å, respectively. Our spectral energy distribution fitting analysis favors the scenario that this object is either a strong broad-line emitter or even a super-Eddington accreting black hole (BH), although a possibility of an extremely young galaxy with moderate dust attenuation is not completely ruled out. The bolometric luminosity, L bol = 2.5 ± 0.3 × 1044 erg s-1, is consistent with those of z < 0.35 broad-line AGNs with M BH ~ 106 M ⊙ accreting at the Eddington limit. This new AGN population in the first 1.1 billion years of the universe may close the gap between the observed BH mass range at high redshift and that of BH seeds. Spectroscopic confirmation is awaited to secure the redshift and its AGN nature.

Keywords: supermassive black holes; reionization; quasars; low-luminosity active galactic nuclei
Gravitational-wave Merger Forecasting: Scenarios for the Early Detection and Localization of Compact-binary Mergers with Ground-based Observatories

We present the prospects for the early (pre-merger) detection and localization of compact-binary coalescences using gravitational waves over the next 10 yr. Early warning can enable the direct observation of the prompt and early electromagnetic emission of a neutron star merger. We examine the capabilities of the ground-based detectors at their "Design" sensitivity (2021-2022), the planned "A+" upgrade (2024-2026), and the envisioned "Voyager" concept (late 2020s). We find that for a fiducial rate of binary neutron star mergers of 1000 Gpc-3 yr-1, the Design, A+, and Voyager era networks can provide 18, 54, and 195 s of warning for one source per year of observing, respectively, with a sky localization area <100 deg2 at a 90% credible level. At the same rate, the A+ and Voyager era networks will be able to provide 9 and 43 s of warning, respectively, for a source with <10 deg2 localization area. We compare the idealized search sensitivity to that achieved by the PyCBC Live search tuned for pre-merger detection. The gravitational-wave community will be prepared to produce pre-merger alerts. Our results motivate the operation of observatories with wide fields of view, automation, and the capability for fast slewing to observe simultaneously with the gravitational-wave network.

Keywords: gravitational wave astronomy
Formulating Compressive Strength of Dust Aggregates from Low to High Volume Filling Factors with Numerical Simulations

Compressive strength is a key to understanding the internal structure of dust aggregates in protoplanetary disks and their resultant bodies, such as comets and asteroids in the solar system. Previous work has modeled the compressive strength of highly porous dust aggregates with volume filling factors lower than 0.1. However, a comprehensive understanding of the compressive strength from low (<0.1) to high (>0.1) volume filling factors is lacking. In this paper, we investigate the compressive strength of dust aggregates by using aggregate compression simulations resolving constituent grains based on Johnson-Kendall-Roberts theory to formulate the compressive strength comprehensively. We perform a series of numerical simulations with moving periodic boundaries mimicking the compression behavior. As a result, we find that the compressive strength becomes sharply harder when the volume filling factor exceeds 0.1. We succeed in formulating the compressive strength comprehensively by taking into account the rolling motion of aggregates for low volume filling factors and the closest packing of aggregates for high volume filling factors. We also find that the dominant compression mechanisms for high volume filling factors are sliding and twisting motions, while rolling motion dominates for low volume filling factors. We confirm that our results are in good agreement with previous numerical studies. We suggest that our analytical formula is consistent with the previous experimental results if we assume the surface energy of silicate is ≃210 ± 90 mJ m-2. Now, we can apply our results to properties of small compact bodies, such as comets, asteroids, and pebbles.

Keywords: planet formation; protoplanetary disks; planetesimals; astronomical simulations; analytical mathematics; computational astronomy
A Plasmoid model for the Sgr A* Flares Observed With Gravity and CHANDRA

The Galactic Center black hole Sgr A* shows significant variability and flares in the submillimeter, infrared, and X-ray wavelengths. Owing to its exquisite resolution in the IR bands, the GRAVITY experiment for the first time spatially resolved the locations of three flares and showed that a bright region moves in ellipse-like trajectories close to, but offset from, the black hole over the course of each event. We present a model for plasmoids that form during reconnection events and orbit in the coronal region around a black hole to explain these observations. We utilize general-relativistic radiative-transfer calculations that include effects from finite light travel time, plasmoid motion, particle acceleration, and synchrotron cooling, and obtain a rich structure in the flare light curves. This model can naturally account for the observed motion of the bright regions observed by the GRAVITY experiment and the offset between the center of the centroid motion and the position of the black hole. It also explains why some flares may be double peaked while others have only a single peak and uncovers a correlation between the structure in the light curve and the location of the flare. Finally, we make predictions for future observations of flares from the inner accretion flow of Sgr A* that will provide a test of this model.

Keywords: black hole physics; high energy astrophysics
Retrieved Atmospheres and Inferred Surface Properties for Terrestrial Exoplanets Using Transmission and Reflected-light Spectroscopy

Future astrophysics missions will seek extraterrestrial life via transmission and direct-imaging observations. To assess habitability and biosignatures, we need robust retrieval tools to analyze observed spectra, and infer surface and atmospheric properties with their uncertainties. We use a novel retrieval tool to assess accuracy in characterizing near-surface habitability and biosignatures via simulated transmission and direct-imaging spectra, based on the Origins Space Telescope (Origins) and LUVOIR mission concepts. We assess our ability to discriminate between an Earth-like and a false-positive O3 TRAPPIST-1 e with transmission spectroscopy. In reflected light, we assess the robustness of retrieval results to unmodeled cloud extinction. We find that assessing habitability using transmission spectra may be challenging due to relative insensitivity to surface temperature and near-surface H2O abundances. Nonetheless, our order-of-magnitude H2O constraints can discriminate extremely desiccated worlds. Direct imaging is insensitive to surface temperature and subject to the radius/albedo degeneracy, but this method proves highly sensitive to surface water abundance, achieving retrieval precision within 0.1% even with partial clouds. Concerning biosignatures, Origins-like transmission observations (t = 40 hr) may detect the CO2/CH4 pair on M-dwarf planets and differentiate between biological and false-positive O3 using H2O and abundant CO. In contrast, direct-imaging observations with LUVOIR-A (t = 10 hr) are better suited to constraining O2 and O3, and may be sensitive to wavelength-dependent water cloud features, but will struggle to detect modern-Earth-like abundances of methane. For direct imaging, we weakly detect a stratospheric ozone bulge by fitting the near-UV wings of the Hartley band.

Keywords: exoplanet atmospheres; exoplanet atmospheric composition; planetary atmospheres; exoplanet atmospheric structure; extrasolar rocky planets; habitable planets; exoplanets; biosignatures; astrobiology
The Impact of the Explicit Representation of Convection on the Climate of a Tidally Locked Planet in Global Stretched-mesh Simulations

Convective processes are crucial in shaping exoplanetary atmospheres but are computationally expensive to simulate directly. A novel technique of simulating moist convection on tidally locked exoplanets is to use a global 3D model with a stretched mesh. This allows us to locally refine the model resolution to 4.7 km and resolve fine-scale convective processes without relying on parameterizations. We explore the impact of mesh stretching on the climate of a slowly rotating TRAPPIST-1e-like planet, assuming it is 1:1 tidally locked. In the stretched-mesh simulation with explicit convection, the climate is 5 K colder and 25% drier than that in the simulations with parameterized convection(with both stretched and quasi-uniform meshes). This is due to the increased cloud reflectivity—because of an increase in low-level cloudiness—and exacerbated by the diminished greenhouse effect due to less water vapor. At the same time, our stretched-mesh simulations reproduce the key characteristics of the global climate of tidally locked rocky exoplanets, without any noticeable numerical artifacts. Our methodology opens an exciting and computationally feasible avenue for improving our understanding of 3D mixing in exoplanetary atmospheres. Our study also demonstrates the feasibility of a global stretched-mesh configuration for LFRic-Atmosphere, the next-generation Met Office climate and weather model.

Keywords: exoplanet atmospheres; exoplanet atmospheric dynamics; exoplanet atmospheric structure; planetary atmospheres; atmospheric clouds; atmospheric dynamics; atmospheric structure; habitable planets; atmospheric circulation
Origin of Weak Mg II and Higher-ionization Absorption Lines in Outflows from Intermediate-redshift Dwarf Galaxies

Observations at intermediate redshifts reveal the presence of numerous compact, weak Mg II absorbers with near to supersolar metallicities, often surrounded by extended regions that produce C IV and/or O VI absorption, in the circumgalactic medium at large impact parameters from luminous galaxies. Their origin and nature remain unclear. We hypothesize that undetected satellite dwarf galaxies are responsible for producing some of these weak Mg II absorbers. We test our hypothesis using gas dynamical simulations of galactic outflows from a dwarf galaxy with a halo mass of 5 × 109 M⊙, as might be falling into a larger L* halo at z = 2. We find that thin, filamentary, weak Mg II absorbers (≲100 pc) are produced in two stages: (1) when shocked core-collapse supernova (SN II)-enriched gas descending in a galactic fountain gets shock compressed by upward flows driven by subsequent SN II and cools (phase 1) and, later, (2) during an outflow driven by Type Ia supernovae that shocks and sweeps up pervasive SN II-enriched gas, which then cools (phase 2). The Mg II absorbers in our simulations are continuously generated by shocks and cooling with moderate metallicity ∼0.1-0.2 Z⊙ but low column density <1012 cm-2. They are also surrounded by larger (0.5-1 kpc) C IV absorbers that seem to survive longer. Larger-scale (>1 kpc) C IV and O VI clouds are also produced in both expanding and shocked SN II-enriched gas. Observable ion distributions from our models appear well converged at our standard resolution (12.8 pc). Our simulation highlights the possibility of dwarf galactic outflows producing highly enriched multiphase gas.

Keywords: circumgalactic medium; dwarf galaxies; metal line absorbers; galactic winds; starburst galaxies
Probing the Dipole of the Diffuse Gamma-Ray Background

We measured the dipole of the diffuse γ-ray background (DGB), identifying a highly significant time-independent signal coincidental with that of the Pierre Auger UHECR. The DGB dipole is determined from flux maps in narrow energy bands constructed from 13 yr of observations by the Large Area Telescope (LAT) of the Fermi satellite. The γ-ray maps were clipped iteratively of sources and foregrounds similar to that done for the cosmic infrared background. The clipped narrow energy band maps were then assembled into one broad energy map out to the given energy starting at E = 2.74 GeV, where the LAT beam falls below the sky's pixel resolution. Next we consider cuts in Galactic latitude and longitude to probe residual foreground contaminations from the Galactic plane and center. In the broad energy range 2.74 < E ≤ 115.5 GeV, the measured dipoles are stable with respect to the various Galactic cuts, consistent with an extragalactic origin. The γ-ray sky's dipole/monopole ratio is much greater than that expected from the DGB clustering component and the Compton-Getting effect origin with reasonable velocities. At ≃(6.5-7)% it is similar to the Pierre Auger UHECRs with E UHECR ≥ 8 EeV, pointing to a common origin of the two dipoles. However, the DGB flux associated with the found DGB dipole reaches parity with that of the UHECR around E UHECR ≤ 1 EeV, perhaps arguing for a non-cascading mechanism if the DGB dipole were to come from the higher-energy UHECRs. The signal-to-noise ratio of the DGB dipole is largest in the 5-30 GeV range, possibly suggesting the γ-photons at these energies are the ones related to cosmic rays.

Keywords: high-energy cosmic radiation; ultra-high-energy cosmic radiation
Unifying High- and Low-resolution Observations to Constrain the Dayside Atmosphere of KELT-20b/MASCARA-2b

We present high-resolution dayside thermal emission observations of the exoplanet KELT-20b/MASCARA-2b using the MAROON-X spectrograph. Applying the cross-correlation method with both empirical and theoretical masks and a retrieval analysis, we confirm previous detections of Fe I emission lines and we detect Ni I for the first time in the planet (at 4.7σ confidence). We do not see evidence for additional species in the MAROON-X data, including notably predicted thermal inversion agents TiO and VO, their atomic constituents Ti I and V I, and previously claimed species Fe II and Cr I. We also perform a joint retrieval with existing Hubble Space Telescope/WFC3 spectroscopy and Spitzer/IRAC photometry. This allows us to place bounded constraints on the abundances of Fe I, H2O, and CO, and to place a stringent upper limit on the TiO abundance. The results are consistent with KELT-20b having a solar to slightly supersolar composition atmosphere in terms of the bulk metal enrichment, and the carbon-to-oxygen and iron-to-oxygen ratios. However, the TiO volume mixing ratio upper limit (10-7.6 at 99% confidence) is inconsistent with this picture, which, along with the nondetection of Ti I, points to sequestration of Ti species, possibly due to nightside condensation. The lack of TiO but the presence of a large H2O emission feature in the WFC3 data is challenging to reconcile within the context of 1D self-consistent, radiative-convective models.

Keywords: hot jupiters; exoplanet atmospheres
Energy-preserving Integrators for Post-Newtonian Lagrangian Dynamics

Equations of motion derived from the Euler-Lagrange formula are usually implicit differential equations in terms of accelerations for the post-Newtonian (PN) Lagrangian dynamics of general relativistic problems. Meanwhile, the Legendre transform is in a nonclosed form due to the high nonlinearity of the velocity in the PN Lagrangian. To numerically integrate the exact implicit equations of motion rather than the truncated equations, the nontruncated strategy with an additional iteration for the Legendre transform is needed. In this paper, we aim at exploring energy-preserving methods accompanying the nontruncated strategy for the PN Lagrangian dynamics, once noticing that energy preservation as well as symplecticity is one of the most important properties of the Hamiltonian system that is completely equivalent to the PN Lagrangian. Incorporating the nontruncated strategy into the continuous-stage Runge-Kutta method, we thus propose a novel class of practical energy-preserving schemes. Numerical results from the PN Lagrangian circular restricted three-body problem and the spinning compact binaries show that the proposed numerical scheme is of high efficiency and can preserve energy nearly as accurately as machine precision.

Keywords: compact objects; computational methods; computational astronomy
Evidence That the Occurrence Rate of Hot Jupiters around Sun-like Stars Decreases with Stellar Age

We investigate how the occurrence rate of giant planets (minimum mass > 0.3 M Jup) around Sun-like stars depends on the age, mass, and metallicity of their host stars. We develop a hierarchical Bayesian framework to infer the number of planets per star (NPPS) as a function of both planetary and stellar parameters. The framework fully takes into account the uncertainties in the latter by utilizing the posterior samples for the stellar parameters obtained by fitting stellar isochrone models to the spectroscopic parameters, Gaia DR3 parallaxes, and 2MASS K s-band magnitudes adopting a certain bookkeeping prior. We apply the framework to 46 Doppler giants found around a sample of 382 Sun-like stars from the California Legacy Survey catalog that publishes spectroscopic parameters and search completeness for all the surveyed stars. We find evidence that the NPPS of hot Jupiters (orbital period P = 1-10 days) decreases roughly in the latter half of the main sequence over the timescale of ${ \mathcal O }(\mathrm{Gyr})$ , while that of cold Jupiters (P = 1-10 yr) does not. Assuming that this decrease is real and caused by tidal orbital decay, the modified stellar tidal quality factor ${Q}_{\star }^{{\prime} }$ is implied to be ${ \mathcal O }({10}^{6})$ for a Sun-like main-sequence star orbited by a Jupiter-mass planet with P ≈ 3 days.

Keywords: exoplanet evolution; tidal disruption; hot jupiters; exoplanets; exoplanet astronomy
Energy-releasing Process for the 2013 May 13 X1.7 Limb Flare: A Continued Study

In this paper, we reanalyze the X1.7 class limb flare that occurred on 2013 May 13 (SOL2013-05-13T01:56 UT), concentrating on the energy-releasing process using microwave observations mainly made by Nobeyama and X-ray observations made by RHESSI. The analysis was carried out in the context of EUV observations made by the Atmospheric Imaging Assembly on board Solar Dynamics Observatory. First, we complement the initiation process by showing that the initiation occurred together with material falling from a large-scale overlying prominence, a signature of drainage instability. The usual downward and upward motions of the microwave and X-ray sources are observed from their evolution. However, the microwave source's height shows a recurrent decrease and increase during its overall upward motion; it shows a kind of recurrent contraction and expansion. The time period of the recurrent contraction and expansion corresponds to the period of post-contraction oscillation of EUV loops, and the oscillatory motions are closely correlated with four microwave/hard X-ray peaks that unusually increased nonthermal emission levels by several times. X-ray spectra get hardened during the oscillation. In addition, the rapid contraction of magnetic loops located on the outside of the erupting flux rope occurs 5 minutes after the onset of the flare, showing that the contraction of the peripheral magnetic loops is more likely due to the vortex and sink flows generated by an upward erupting magnetic flux rope rather than a coronal implosion. The results can provide more insight into the physics of dynamic coronal magnetic field and particle acceleration during solar flares.

Keywords: solar flares; solar magnetic reconnection; x-ray sources; solar radio emission; solar activity
Double Shadows at the Lunar Poles

Topographic depressions within permanently shadowed regions (PSRs) on low-obliquity planetary bodies can be shielded not only from direct illumination, but also from scattered sunlight and thermal emission from nearby sunlit surfaces. We apply an illumination model to high-resolution topography data to produce the first map of double shadows at the lunar poles. The total doubly shadowed area resolved at the 30 m scale is 1.47 km2 in the northern hemisphere and 5.37 km2 in the southern hemisphere, predominantly contained within small craters on the floors of large permanently shadowed craters. In total, ~0.04% of PSR area is permanently double shadowed, but the largest double shadows are nearly 600 m across, potentially large enough to be resolved in remote sensing temperature measurements. In the absence of secondary heating sources, double shadows are predicted to be significantly colder than singly shadowed areas and could sequester highly volatile compounds like carbon dioxide. Future in situ investigation of the regions identified in this work can elucidate the origin and distribution of the Moon's most volatile deposits.

Keywords: the moon; planetary polar regions; lunar surface; surface ices