adsabs/SciX_UAT_keywords huggingface dataset:
The Fourth Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope

The fourth catalog of active galactic nuclei (AGNs) detected by the Fermi Gamma-ray Space Telescope Large Area Telescope (4LAC) between 2008 August 4 and 2016 August 2 contains 2863 objects located at high Galactic latitudes (|b| > 10°). It includes 85% more sources than the previous 3LAC catalog based on 4 yr of data. AGNs represent at least 79% of the high-latitude sources in the fourth Fermi-Large Area Telescope Source Catalog (4FGL), which covers the energy range from 50 MeV to 1 TeV. In addition, 344 gamma-ray AGNs are found at low Galactic latitudes. Most of the 4LAC AGNs are blazars (98%), while the remainder are other types of AGNs. The blazar population consists of 24% Flat Spectrum Radio Quasars (FSRQs), 38% BL Lac-type objects, and 38% blazar candidates of unknown types (BCUs). On average, FSRQs display softer spectra and stronger variability in the gamma-ray band than BL Lacs do, confirming previous findings. All AGNs detected by ground-based atmospheric Cerenkov telescopes are also found in the 4LAC.

Keywords: active galactic nuclei; blazars; gamma-ray sources; relativistic jets; quasars; bl lacertae objects
A Model Estimator for Noisy Compact Emission Recovery in Radio Synthesis Imaging

Reconstruction of a noisy compact emission must consider not only the point-spread function but also the effect of noise. However, the traditional threshold method in widely-used CLEAN-based algorithms finds it difficult to effectively prevent noise in the model image during noisy compact-emission reconstruction. This significantly limits the performance in noisy compact-emission reconstruction, such as deep field imaging. There are two major difficulties in the accurate reconstruction of a Stokes-I image of compact emission: first, the threshold method that has been used in practice is difficult to use to separate compact emission and noise; and second, over-subtraction makes it difficult for the reconstructed Stokes-I model image to remain positive. Therefore, a filter-based denoizing mechanism is introduced in the search phase of the model components to separate signal and noise so that the signal can be effectively extracted. The relatively larger loop gain for positive components means that the reconstructed model is in line with astrophysics. This will reduce the errors between the true sky image and the model image. The new model estimator is tested on a simulated JVLA observation with realistic source distributions from the VLA Low-Frequency Sky Survey project and the SKADS/SCubed simulation. The experiments show that it is very effective when used to separate signal and noise to lower the noise in the model image. This work explores the use of existing common software CASA to achieve high dynamic range imaging, which is an important step toward square kilometer array data processing.

Keywords: astronomy data reduction; astronomy data analysis
ACCESS: Confirmation of a Clear Atmosphere for WASP-96b and a Comparison of Light Curve Detrending Techniques

One of the strongest Na I features was observed in WASP-96b. To confirm this novel detection, we provide a new 475-825 nm transmission spectrum obtained with Magellan/IMACS, which indeed confirms the presence of a broad sodium absorption feature. We find the same result when reanalyzing the 400-825 nm VLT/FORS2 data. We also utilize synthetic data to test the effectiveness of two common detrending techniques: (1) a Gaussian processes (GP) routine, and (2) common-mode correction followed by polynomial correction (CMC+Poly). We find that both methods poorly reproduce the absolute transit depths but maintain their true spectral shape. This emphasizes the importance of fitting for offsets when combining spectra from different sources or epochs. Additionally, we find that, for our data sets, both methods give consistent results, but CMC+Poly is more accurate and precise. We combine the Magellan/IMACS and VLT/FORS2 spectra with literature 800-1644 nm HST/WFC3 spectra, yielding a global spectrum from 400 to 1644 nm. We used the PLATON and Exoretrievals retrieval codes to interpret this spectrum, and find that both yield relatively deeper pressures where the atmosphere is optically thick at log-pressures between ${1.3}_{-1.1}^{+1.0}$ and ${0.29}_{-2.02}^{+1.86}$ bars, respectively. Exoretrievals finds solar to supersolar Na I and H2O log-mixing ratios of $-{5.4}_{-1.9}^{+2.0}$ and $-{4.5}_{-2.0}^{+2.0}$ , respectively, while PLATON finds an overall metallicity of ${\mathrm{log}}_{10}(Z/{Z}_{\odot })=-{0.49}_{-0.37}^{+1.0}$ dex. Therefore, our findings are in agreement with the literature and support the inference that the terminator of WASP-96b has few aerosols obscuring prominent features in the optical to near-infrared (near-IR) spectrum.

Keywords: exoplanet atmospheres; observational astronomy; exoplanet astronomy; hot jupiters; transmission spectroscopy
A Sub-Neptune-sized Planet Transiting the M2.5 Dwarf G 9-40: Validation with the Habitable-zone Planet Finder

We validate the discovery of a 2-Earth-radii sub-Neptune-sized planet around the nearby high-proper-motion M2.5 dwarf G 9-40 (EPIC 212048748), using high-precision, near-infrared (NIR) radial velocity (RV) observations with the Habitable-zone Planet Finder (HPF), precision diffuser-assisted ground-based photometry with a custom narrowband photometric filter, and adaptive optics imaging. At a distance of d = 27.9 $\,\mathrm{pc}$ , G 9-40b is the second-closest transiting planet discovered by K2 to date. The planet's large transit depth (∼3500 ppm), combined with the proximity and brightness of the host star at NIR wavelengths (J = 10, K = 9.2), makes G 9-40b one of the most favorable sub-Neptune-sized planets orbiting an M dwarf for transmission spectroscopy with James Webb Space Telescope, ARIEL, and the upcoming Extremely Large Telescopes. The star is relatively inactive with a rotation period of ∼29 days determined from the K2 photometry. To estimate spectroscopic stellar parameters, we describe our implementation of an empirical spectral-matching algorithm using the high-resolution NIR HPF spectra. Using this algorithm, we obtain an effective temperature of ${T}_{\mathrm{eff}}=3404\pm 73\,{\rm{K}}$ and metallicity of $[\mathrm{Fe}/{\rm{H}}]=-0.08\pm 0.13$ . Our RVs, when coupled with the orbital parameters derived from the transit photometry, exclude planet masses above 11.7M⊕ with 99.7% confidence assuming a circular orbit. From its radius, we predict a mass of $M={5.0}_{-1.9}^{+3.8}{M}_{\oplus }$ and an RV semiamplitude of $K={4.1}_{-1.6}^{+3.1}\,{\rm{m}}\ {{\rm{s}}}^{-1}$ , making its mass measurable with current RV facilities. We urge further RV follow-up observations to precisely measure its mass, to enable precise transmission spectroscopic measurements in the future.

Keywords: exoplanet astronomy; exoplanet systems; radial velocity; exoplanet detection methods; transit photometry; low mass stars; mini neptunes; exoplanets
Generic Models for Disk-resolved and Disk-integrated Phase-dependent Linear Polarization of Light Reflected from Exoplanets

Similar to the case of solar system planets, reflected starlight from exoplanets is expected to be polarized due to atmospheric scattering, and the net disk-integrated polarization should be nonzero owing to the asymmetrical illumination of the planetary disk. The computation of the disk-integrated reflected flux and its state of polarization involves techniques for the calculation of the local reflection matrices, as well as the numerical recipes for integration over the planetary disks. In this paper, we present a novel approach to calculate the azimuth-dependent reflected intensity vectors at each location on the planetary disk divided into grids. We achieve this by solving the vector radiative transfer equations that describe linear polarization. Our calculations incorporate self-consistent atmospheric models of exoplanets over a wide range of equilibrium temperature, surface gravity, atmospheric composition, and cloud structure. A comparison of the flux and the amount of polarization calculated by considering both single and multiple scattering exhibits the effect of depolarization due to multiple scattering of light depending on the scattering albedo of the atmosphere. We have benchmarked our basic calculations against some of the existing models. We have also presented our models for the hot Jupiter HD 189733 b, indicating the level of precision required by future observations to detect the polarization of this planet in the optical and near-infrared wavelength region. The generic nature and the accuracy offered by our models make them an effective tool for modeling future observations of the polarized light reflected from exoplanets.

Keywords: exoplanet atmospheres; polarimetry; exoplanet atmospheric composition; exoplanets; hot jupiters
Research, Experiment and Validation of Adaptive Optics with a Legacy Telescope (REVOLT): First On-sky Results

The first on-sky results of the Research, Experiment and Validation of Adaptive Optics with a Legacy Telescope (REVOLT) project are presented, along with a description of the project and its purpose. The REVOLT project has so far demonstrated successful closed loop, single conjugate adaptive optics using a natural guide star at the 1.22 m McKellar telescope at the Dominion Astrophysical Observatory in Victoria, BC, Canada. In so doing, we have made the first on-sky demonstration of the Herzberg Extensible Adaptive Realtime Toolkit-based Real Time Controller, and First Light Imaging's C-Blue One camera.

Keywords: adaptive optics; astronomical instrumentation; astronomical detectors
A Consistent Explanation for the Unusual Initial Mass Function and Star Formation Rate in the Central Molecular Zone (CMZ)

We examine various physical processes that may explain the shallow high-mass slope of the initial mass function (IMF), as well as the low star formation rate (SFR) in star-forming molecular clouds (MCs) in the Central Molecular Zone (CMZ). We show that the strong tidal field and shear experienced by the CMZ have opposite effects on the collapse of density fluctuations and cannot explain these properties. Similarly, we show that the intense magnetic field in the CMZ provides a negligible pressure support and, for the high densities at play, should not modify the probability density function of the turbulent gas flow, thus affecting negligibly the IMF. However, we show that, in contrast to the MCs in the Galactic disk, the ones in the CMZ experience only one single episode of turbulence cascade. Indeed, their rather short lifetime, due to their high mean densities, is similar to one typical turbulence crossing time. Consequently, according to the Hennebelle–Chabrier theory of star formation, within this "single turbulence cascade episode," the cloud experiences one single field of turbulence-induced density fluctuations, leading eventually to gravitationally unstable cores. As shown in Hennebelle & Chabrier (2013), this yields a shallower IMF than usual and leads to the correct observed slope for the CMZ star-forming clouds. Similarly, this single large-scale turbulence event within the cloud lifetime yields a 5–6 times lower SFR than under usual conditions, in agreement with the observed values. Therefore, we suggest that this "single turbulence cascade" scenario can explain both the shallow IMF and low SFR of clouds in the CMZ.

Keywords: milky way galaxy
CEERS Key Paper. VI. JWST/MIRI Uncovers a Large Population of Obscured AGN at High Redshifts

Mid-infrared (mid-IR) observations are powerful in identifying heavily obscured active galactic nuclei (AGN) that have weak emission in other wavelengths. Data from the Mid-Infrared Instrument (MIRI) on board the James Webb Space Telescope provides an excellent opportunity to perform such studies. We take advantage of the MIRI imaging data from the Cosmic Evolution Early Release Science Survey to investigate the AGN population in the distant universe. We estimate the source properties of MIRI-selected objects by utilizing spectral energy distribution (SED) modeling, and classify them into star-forming galaxies (SFs), SF-AGN mixed objects, and AGN. The source numbers of these types are 433, 102, and 25, respectively, from four MIRI pointings covering ~9 arcmin2. The sample spans a redshift range of ≈0-5. We derive the median SEDs for all three source types, respectively, and publicly release them. The median MIRI SED of AGN is similar to the typical SEDs of hot dust-obscured galaxies and Seyfert 2s, for which the mid-IR SEDs are dominated by emission from AGN-heated hot dust. Based on our SED-fit results, we estimate the black hole accretion density (BHAD; i.e., total BH growth rate per comoving volume) as a function of redshift. At z < 3, the resulting BHAD agrees with the X-ray measurements in general. At z > 3, we identify a total of 27 AGN and SF-AGN mixed objects, leading to that our high-z BHAD is substantially higher than the X-ray results (~0.5 dex at z ≈ 3-5). This difference indicates MIRI can identify a large population of heavily obscured AGN missed by X-ray surveys at high redshifts.

Keywords: active galactic nuclei; high-redshift galaxies; supermassive black holes; star formation
The Star Formation Efficiency during Reionization as Inferred from the Hubble Frontier Fields

A recent ultraviolet luminosity function (UVLF) analysis in the Hubble Frontier Fields, behind foreground lensing clusters, has helped solidify estimates of the faint-end of the z ~ 5-9 UVLF at up to 5 mag fainter than in the field. These measurements provide valuable information regarding the role of low-luminosity galaxies in reionizing the universe and can help in calibrating expectations for JWST observations. We fit a semiempirical model to the lensed and previous UVLF data from Hubble. This fit constrains the average star formation efficiency (SFE) during reionization, with the lensed UVLF measurements probing halo mass scales as small as M ~ 2 × 109 M ⊙. The implied trend of SFE with halo mass is broadly consistent with an extrapolation from previous inferences at M ≳ 1010 M ⊙, although the joint data prefer a shallower SFE. This preference, however, is partly subject to systematic uncertainties in the lensed measurements. Near z ~ 6, we find that the SFE peaks at ~20% between ~1011 and 1012 M ⊙. Our best-fit model is consistent with the Planck 2020 determinations of the electron scattering optical depth, and most current reionization history measurements, provided the escape fraction of ionizing photons is f esc ~ 10%-20%. The joint UVLF accounts for nearly 80% of the ionizing photon budget at z ~ 8. Finally, we show that recent JWST UVLF estimates at z ≳ 11 require strong departures from the redshift evolution suggested by the Hubble data.

Keywords: luminosity function; star formation; reionization; hubble space telescope; galaxy dark matter halos; gravitational lensing; james webb space telescope; stellar feedback; astronomical models; model selection; markov chain monte carlo
SOAR TESS Survey. II. The Impact of Stellar Companions on Planetary Populations

We present the results of the second year of exoplanet candidate host speckle observations from the SOAR TESS survey. We find 89 of the 589 newly observed TESS planet candidate hosts have companions within 3″, resulting in light-curve dilution, that, if not accounted for, leads to underestimated planetary radii. We combined these observations with those from Paper I to search for evidence of the impact binary stars have on planetary systems. Removing the one-quarter of the targets observed identified as false-positive planet detections, we find that transiting planets are suppressed by nearly a factor of seven in close solar-type binaries, nearly twice the suppression previously reported. The result on planet occurrence rates that are based on magnitude-limited surveys is an overestimation by a factor of two if binary suppression is not taken into account. We also find tentative evidence for similar close binary suppression of planets in M-dwarf systems. Last, we find that the high rates of widely separated companions to hot Jupiter hosts previously reported was likely a result of false-positive contamination in our sample.

Keywords: binary stars; companion stars; exoplanet astronomy; exoplanet dynamics; speckle interferometry
Halo Counts-in-cells for Cosmological Models with Different Dark Energy

We examine the counts-in-cells (CiC) probability distribution functions (PDFs) that describe dark matter halos in the Dark Energy Universe Simulations (DEUS). We describe the measurements between redshifts z = 0 to z = 4 on both linear and nonlinear scales. The best fits of the gravitational quasi-equilibrium distribution (GQED), the negative binomial distribution (NBD), the Poisson-Lognormal distribution (PLN), and the Poisson-Lognormal distribution with a bias parameter (PLNB) are compared to simulations. The fits agree reasonably consistently over a range of redshifts and scales. To distinguish quintessence (RPCDM) and phantom (wCDM) dark energy from Λ dark energy, we present a new method that compares the model parameters of the CiC PDFs. We find that the mean and variance of the halo CiC on 2-25h-1 Mpc scales between redshifts 0.65 < z < 4 show significant percentage differences for different dark energy cosmologies. On 15-25 h-1 Mpc scales, the g parameter in NBD, ω parameter in PLN, and b and Cb parameters in PLNB show larger percentage differences for different dark energy cosmologies than on smaller scales. On 2-6 h-1 Mpc scales, the kurtosis and the b parameter in the GQED show larger percentage differences for different dark energy cosmologies than on larger scales. For cosmologies explored in the DEUS, the percentage differences between these statistics for the RPCDM and wCDM dark energy cosmologies relative to ΛCDM generally increases with redshift from a few percent to significantly larger percentages at z = 4. Applying our method to simulations and galaxy surveys can provide a useful way to distinguish among dark energy models and cosmologies in general.

Keywords: cosmology; dark matter; dark energy; large-scale structure of the universe; theoretical models
A Proper Discretization of Hydrodynamic Equations in Cylindrical Coordinates for Astrophysical Simulations

Cylindrical coordinates are often used in computational fluid dynamics, particularly when one is considering gas flow accreting onto a central object. Although cylindrical coordinates have several advantages in describing rotation, they have apparent singularity along the axis at the coordinate origin (z-axis). This singularity introduces difficulties in numerical simulations. First, it is difficult to reproduce the flow across the z-axis. Second, the time step is extremely shortened by the CFL condition near the z-axis because the numerical cell thereof is narrow in the azimuthal direction for a given angular resolution. Here, we propose a new discretization scheme to overcome these difficulties. In our new scheme, we consider changes in the direction of the unit vector within a cell when evaluating the flux across each cell surface. Besides, we evaluate the source term in the radial component of the momentum equation from the thermal and dynamic pressures acting on the azimuthal cell surface. The new scheme is designed to be free-stream-preserving so that flow with uniform density, pressure, and velocity is an exact solution of the discretized equation. These improvements are essential to using a lower angular resolution in the innermost area and thus to elongating each time step. Our examples demonstrate that the innermost circular region around the axis can be resolved by only six numerical cells. We present an application to an accreting compact star surrounded by a disk, in addition to Sod shock tube and rotating outflow tests.

Keywords: hydrodynamics; hydrodynamical simulations; astronomical simulations
Alfvénic Motions Arising from Asymmetric Acoustic Wave Drivers in Solar Magnetic Structures

Alfvénic motions are ubiquitous in the solar atmosphere and their observed properties are closely linked to those of photospheric p-modes. However, it is still unclear how a predominantly acoustic wave driver can produce these transverse oscillations in the magnetically dominated solar corona. In this study we conduct a 3D ideal MHD numerical simulation to model a straight, expanding coronal loop in a gravitationally stratified solar atmosphere which includes a transition region and chromosphere. We implement a driver locally at one foot-point corresponding to an acoustic-gravity wave which is inclined by θ = 15° with respect to the vertical axis of the magnetic structure and is similar to a vertical driver incident on an inclined loop. We show that transverse motions are produced in the magnetic loop, which displace the axis of the waveguide due to the breaking of azimuthal symmetry, and study the resulting modes in the theoretical framework of a magnetic cylinder model. By conducting an azimuthal Fourier analysis of the perturbed velocity signals, the contribution from different cylindrical modes is obtained. Furthermore, the perturbed vorticity is computed to demonstrate how the transverse motions manifest themselves throughout the whole non-uniform space. Finally we present some physical properties of the Alfvénic perturbations and present transverse motions with velocity amplitudes in the range 0.2-0.75 km s-1 which exhibit two distinct oscillation regimes corresponding to 42 and 364 s, where the latter value is close to the period of the p-mode driver in the simulation.

Keywords: magnetohydrodynamics; solar atmosphere; solar chromosphere; solar oscillations; solar coronal loops; solar coronal waves; magnetohydrodynamical simulations
From Active Stars to Black Holes: A Discovery Tool for Galactic X-Ray Sources

Galactic X-ray sources are diverse, ranging from active M dwarfs to compact object binaries, and everything in between. The X-ray landscape of today is rich, with point source catalogs such as those from XMM-Newton, Chandra, and Swift, each with ≳105 sources and growing. Furthermore, X-ray astronomy is on the verge of being transformed through data releases from the all-sky SRG/eROSITA survey. Many X-ray sources can be associated with an optical counterpart, which in the era of Gaia, can be determined to be Galactic or extragalactic through parallax and proper motion information. Here, I present a simple diagram—the "X-ray Main Sequence," which distinguishes between compact objects and active stars based on their optical color and X-ray-to-optical flux ratio (F X/F opt). As a proof of concept, I present optical spectroscopy of six exotic accreting WDs discovered using the X-ray Main Sequence as applied to the XMM-Newton catalog. Looking ahead to surveys of the near future, I additionally present SDSS-V optical spectroscopy of new systems discovered using the X-ray Main Sequence as applied to the SRG/eROSITA eFEDS catalog.

Keywords: x-ray astronomy; binary stars; cataclysmic variable stars; rs canum venaticorum variable stars; variable stars; astronomy data visualization; x-ray stars