adsabs/SciX_UAT_keywords huggingface dataset:
Assessment of the Presence of PAHs and Hydrogenated PAHs in the Young Stellar Object Mon R2 and the Taurus Dense Cloud Toward Elias 16

This study assesses the contribution of neutral polycyclic aromatic hydrocarbons (PAHs) and hydrogenated PAHs (Hn-PAHs) in H2O-ices to the 3 μm and 5-8 μm regions of the infrared absorption spectrum of the Young Stellar Object, Mon R2 IRS 3, and the Taurus dense cloud in the direction of Elias 16. We compare the astronomical spectra to the previously published laboratory data of matrix-isolated PAHs and Hn-PAHs in H2O-ices. For the molecules in this study, the band positions, FWHMs, and integrated band strengths have been measured. For the PAHs considered here, the ratio of the experimental A(C-H) stretch (in H2O ices) to the theoretical A(C-H) stretch (in the gas phase) is consistently about 0.10, meaning that the trove of theoretical data can be reliably scaled to compare to the astronomical spectra. We find that the fractional percentage contribution to the 5-8 μm region for Mon R2 IRS 3 ranges between 2.7 and 3.9 for neutral PAHs and 0.25-1.2 for Hn-PAHs. The best match to the observed 3.25 μm profile in the Mon R2 IRS 3 spectrum is accomplished with the laboratory-measured coronene:H2O spectrum. Using this spectrum we estimate that neutral PAHs contribute up to 12.0% of the cosmic carbon budget for Mon R2 IRS 3 and <14.5% for Elias 16. Neutral hydrogenated PAHs contribute mainly to the 3.47 μm absorption and very little to the 5 to 8 μm region. For neutral Hn-PAHs, we estimate that they contribute up to 0.6% of the cosmic carbon budget for Mon R2 IRS 3 and <1% for Elias 16.

Keywords: astrochemistry
A Census of the Bright z = 8.5-11 Universe with the Hubble and Spitzer Space Telescopes in the CANDELS Fields

We present the results from a new search for candidate galaxies at z ≈ 8.5-11 discovered over the 850 arcmin2 area probed by the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS). We use a photometric-redshift selection including both Hubble and Spitzer Space Telescope photometry to robustly identify galaxies in this epoch at H 160 < 26.6. We use a detailed vetting procedure, including screening against persistence and stellar contamination, and the inclusion of ground-based imaging and follow-up Hubble Space Telescope imaging to build a robust sample of 11 candidate galaxies, three presented here for the first time. The inclusion of Spitzer/IRAC photometry in the selection process reduces contamination, and yields more robust redshift estimates than Hubble alone. We constrain the evolution of the rest-frame ultraviolet luminosity function via a new method of calculating the observed number densities without choosing a prior magnitude bin size. We find that the abundance at our brightest probed luminosities (M UV = - 22.3) is consistent with predictions from simulations that assume that galaxies in this epoch have gas depletion times at least as short as those in nearby starburst galaxies. Due to large Poisson and cosmic variance uncertainties, we cannot conclusively rule out either a smooth evolution of the luminosity function continued from z = 4-8, or an accelerated decline at z > 8. We calculate that the presence of seven galaxies in a single field Extended Groth Strip is an outlier at the 2σ significance level, implying the discovery of a significant over-density. These scenarios will be imminently testable to high confidence within the first year of observations of the James Webb Space Telescope.

Keywords: reionization; galaxy evolution; galaxy formation
The Nonsingular Estimator for Exoplanet Orbits: An Unscented Batch Estimation Method for Direct Imaging Measurements

We present a new method for fitting exoplanet orbits to direct astrometric measurements, using nonlinear batch estimation and nonsingular orbital elements. Our estimation technique is based on the unscented transform, which approximates probability distributions using finite, deterministic sets of weighted sample points. Furthermore, we use Gaussian mixtures to account for the strong nonlinearities in the measurement model. As a fitting basis, we use a set of orbital elements developed specifically for directly observed exoplanets, combining features of the Thiele–Innes constants and the Cohen–Hubbard nonsingular elements. We validate the new method using simulated exoplanet orbits, and we demonstrate its use with real exoplanet data. Compared to state-of-the-art Markov Chain Monte Carlo and Bayesian rejection sampling techniques, the new method is found to give orbit estimates of comparable or higher accuracy but with much faster execution.

Keywords: exoplanets; direct imaging; orbit determination; orbital elements
Discovery of a Fast-expanding Shell in the Inside-out Born-again Planetary Nebula HuBi 1 through High-dispersion Integral Field Spectroscopy

HuBi 1 has been proposed to be member of the rare class of born-again planetary nebulae (PNe), i.e., its central star experienced a very late thermal pulse and ejected highly processed material at high speeds inside the old hydrogen-rich PN. In this Letter we present GTC MEGARA integral field spectroscopic observations of the innermost regions of HuBi 1 at high spectral resolution ≃16 km s-1 and multi-epoch subarcsecond images obtained ≃12 yr apart. The analysis of these data indicates that the inner regions of HuBi 1 were ejected ≃200 yr ago and expand at velocities ≃300 km s-1, in excellent agreement with the born-again scenario. The unprecedented tomographic capabilities of the GTC MEGARA high-dispersion observations used here reveal that the ejecta in HuBi 1 has a shell-like structure, in contrast to the disrupted disk and jet morphology of the ejecta in other born-again PNe.

Keywords: planetary nebulae; jets; stellar evolution; interstellar medium
HYPHY: Deep Generative Conditional Posterior Mapping of Hydrodynamical Physics

Generating large-volume hydrodynamical simulations for cosmological observables is a computationally demanding task necessary for next-generation observations. In this work, we construct a novel fully convolutional variational autoencoder (VAE) to synthesize hydrodynamic fields conditioned on dark matter fields from N-body simulations. After training the model on a single hydrodynamical simulation, we are able to probabilistically map new dark-matter-only simulations to corresponding full hydrodynamical outputs. By sampling over the latent space of our VAE, we can generate posterior samples and study the variance of the mapping. We find that our reconstructed field provides an accurate representation of the target hydrodynamical fields as well as reasonable variance estimates. This approach has promise for the rapid generation of mocks as well as for implementation in a full inverse model of observed data.

Keywords: intergalactic medium; extragalactic astronomy; intergalactic gas; convolutional neural networks; neural networks
Paschen-line Constraints on Dust Attenuation and Star Formation at z 1-3 with JWST/NIRSpec

We use medium-resolution JWST/NIRSpec observations from the Cosmic Evolution Early Release Science Survey to place the first constraints on dust attenuation and star formation based on Paschen lines for a sizable sample of 63 galaxies at redshifts z = 1.0-3.1. Our analysis indicates strong correlations between the Balmer decrement, Hα/Hβ, and line ratios that include Paschen lines (i.e., Paα/Hβ, Paβ/Hβ, and the Paschen decrement, Paα/Paβ), suggesting that the former is sensitive to the overall dust obscuration toward H II regions in high-redshift galaxies. The line ratios are used to derive nebular reddening, E(B - V)neb, and star formation rates (SFRs). There is marginal evidence that the SFRs deduced from Paschen lines may exceed by ≈25% those derived from Balmer lines alone, suggesting the presence of star formation that is optically thick in Balmer lines, though deeper observations are needed to confirm this result. Using the Paschen-line constraints on the bolometric SFRs, we reevaluate the relationship between dust obscuration and UV spectral slope, and find a reddening of the UV continuum that, on average, follows the SMC extinction curve. This analysis highlights the need for deeper spectroscopy of more representative samples to evaluate nebular dust attenuation and bolometric SFRs in high-redshift galaxies, and their relationship to the reddening of the UV continuum.

Keywords: interstellar dust extinction; galaxy evolution; high-redshift galaxies; interstellar medium; star formation
A Generalized Analytical Model for Thermal and Bulk Comptonization in Accretion-powered X-Ray Pulsars

We develop a new theoretical model describing the formation of the radiation spectrum in accretion-powered X-ray pulsars as a result of bulk and thermal Comptonization of photons in the accretion column. The new model extends the previous model developed by the authors in four ways: (1) we utilize a conical rather than cylindrical geometry; (2) the radiation components emitted from the column wall and the column top are computed separately; (3) the model allows for a nonzero impact velocity at the stellar surface; and (4) the velocity profile of the gas merges with Newtonian freefall far from the star. We show that these extensions allow the new model to simulate sources over a wide range of accretion rates. The model is based on a rigorous mathematical approach in which we obtain an exact series solution for the Green's function describing the reprocessing of monochromatic seed photons. Emergent spectra are then computed by convolving the Green's function with bremsstrahlung, cyclotron, and blackbody photon sources. The range of the new model is demonstrated via applications to the high-luminosity source Her X-1, and the low-luminosity source X Per. The new model suggests that the observed increase in spectral hardness associated with increasing luminosity in Her X-1 may be due to a decrease in the surface impact velocity, which increases the PdV work done on the radiation field by the gas.

Keywords: neutron stars; x-ray binary stars; radiative processes
Continued Radio Observations of GW170817 3.5 yr Post-merger

We present new radio observations of the binary neutron star merger GW170817 carried out with the Karl G. Jansky Very large Array (VLA) more than 3 yr after the merger. Our combined data set is derived by coadding more than ≈32 hr of VLA time on-source, and as such provides the deepest combined observation (rms sensitivity ≈0.99 μJy) of the GW170817 field obtained to date at 3 GHz. We find no evidence for a late-time radio rebrightening at a mean epoch of t ≈ 1200 days since merger, in contrast to a ≈2.1σ excess observed at X-ray wavelengths at the same mean epoch. Our measurements agree with expectations from the post-peak decay of the radio afterglow of the GW170817 structured jet. Using these results, we constrain the parameter space of models that predict a late-time radio rebrightening possibly arising from the high-velocity tail of the GW170817 kilonova ejecta, which would dominate the radio and X-ray emission years after the merger (once the structured jet afterglow fades below detection level). Our results point to a steep energy-speed distribution of the kilonova ejecta (with energy-velocity power-law index α ≳ 5). We suggest possible implications of our radio analysis, when combined with the recent tentative evidence for a late-time rebrightening in the X-rays, and highlight the need for continued radio-to-X-ray monitoring to test different scenarios.

Keywords: radio continuum emission; radio transient sources; x-ray transient sources
Asteroseismic Modeling of Gravity Modes in Slowly Rotating A/F Stars with Radiative Levitation

It has been known for several decades that transport of chemical elements is induced by the process of microscopic atomic diffusion. Yet the effect of atomic diffusion, including radiative levitation, has hardly been studied in the context of gravity-mode pulsations of core hydrogen burning stars. In this paper we study the difference in the properties of such modes for models with and without atomic diffusion. We perform asteroseismic modeling of two slowly rotating A- and F-type pulsators, KIC 11145123 ( ${f}_{\mathrm{rot}}$ $\approx \,0.010\,{\mathrm{day}}^{-1}$ ) and KIC 9751996 ( ${f}_{\mathrm{rot}}$ $\approx \,0.0696\,{\mathrm{day}}^{-1}$ ), respectively, based on the periods of individual gravity modes. For both stars, we find models whose g-mode periods are in very good agreement with the Kepler asteroseismic data, keeping in mind that the theoretical/numerical precision of present-day stellar evolution models is typically about two orders of magnitude lower than the measurement errors. Using the Akaike Information Criterion, we have made a comparison between our best models with and without diffusion and found very strong evidence for signatures of atomic diffusion in the pulsations of KIC 11145123. In the case of KIC 9751996 the models with atomic diffusion are not able to explain the data as well as the models without it. Furthermore, we compare the observed surface abundances with those predicted by the best-fitting models. The observed abundances are inconclusive for KIC 9751996, while those of KIC 11145123 from the literature can better be explained by a model with atomic diffusion.

Keywords: asteroseismology; stellar abundances; stellar evolution; stellar oscillations; stellar processes; stellar properties
Baryon-induced Collapse of Dark Matter Cores into Supermassive Black Holes

Nonlinear structure formation for fermionic dark matter particles leads to dark matter density profiles with a degenerate compact core surrounded by a diluted halo. For a given fermion mass, the core has a critical mass that collapses into a supermassive black hole (SMBH). Galactic dynamics constraints suggest a ~100 keV/c 2 fermion, which leads to ~107 M ⊙ critical core mass. Here, we show that baryonic (ordinary) matter accretion drives an initially stable dark matter core to SMBH formation and determines the accreted mass threshold that induces it. Baryonic gas density ρ b and velocity v b inferred from cosmological hydrosimulations and observations produce sub-Eddington accretion rates triggering the baryon-induced collapse in less than 1 Gyr. This process produces active galactic nuclei in galaxy mergers and the high-redshift Universe. For TXS 2116-077, merging with a nearby galaxy, the observed 3 × 107 M ⊙ SMBH, for ${Q}_{b}={\rho }_{b}/{v}_{b}^{3}=0.125{M}_{\odot }/{(100\,\mathrm{km}\,{{\rm{s}}}^{-1}\,\mathrm{pc})}^{3}$ , forms in ≈0.6 Gyr, consistent with the 0.5-2 Gyr merger timescale and younger jet. For the farthest central SMBH detected by the Chandra X-ray satellite in the z = 10.3 UHZ1 galaxy observed by the James Webb Space Telescope (JWST), the mechanism leads to a 4 × 107 M ⊙ SMBH in 87-187 Myr, starting the accretion at z = 12-15. The baryon-induced collapse can also explain the ≈107-108 M ⊙ SMBHs revealed by JWST at z ≈ 4-6. After its formation, the SMBH can grow to a few 109 M ⊙ in timescales shorter than 1 Gyr via sub-Eddington baryonic mass accretion.

Keywords: high-redshift galaxies; active galactic nuclei; supermassive black holes; galaxy dark matter halos; dark matter; gravitational collapse
Modeling Type Ic Supernovae with TARDIS: Hidden Helium in SN 1994I?

Supernovae (SNe) with photospheric spectra devoid of hydrogen and helium features are generally classified as SNe Ic. However, there is ongoing debate as to whether helium can be hidden in the ejecta of SNe Ic (that is, helium is present in the ejecta, but produces no obvious features in the spectra). We present the first application of the fast, 1D radiative transfer code TARDIS to an SN Ic, and we investigate the question of how much helium can be hidden in the outer layers of the SN Ic ejecta. We generate TARDIS models for the nearby, well-observed, and extensively modeled SN Ic 1994I, and we perform a code comparison to a different, well-established Monte Carlo based radiation transfer code. The code comparison shows that TARDIS produces consistent synthetic spectra for identical ejecta models of SN 1994I. In addition, we perform a systematic experiment of adding outer He shells of varying masses to our SN 1994I models. We find that an outer He shell of only 0.05M⊙ produces strong optical and near-infrared (NIR) He spectral features for SN 1994I which are not present in observations, thus indicating that the SN 1994I ejecta is almost fully He deficient compared to the He masses of typical He-rich SN progenitors. Finally we show that the He I λ20851 line pseudo-equivalent width of our modeled spectra for SN 1994I could be used to infer the outer He shell mass which suggests that NIR spectral follow-up of SNe Ic will be critical for addressing the hidden helium question for a statistical sample of SNe Ic.

Keywords: type ic supernovae; core-collapse supernovae; radiative transfer; astronomy data modeling
Probing the Intergalactic Turbulence with Fast Radio Bursts

The turbulence in the diffuse intergalactic medium (IGM) plays an important role in various astrophysical processes across cosmic time, but it is very challenging to constrain its statistical properties both observationally and numerically. Via the statistical analysis of turbulence along different sight lines toward a population of fast radio bursts (FRBs), we demonstrate that FRBs provide a unique tool to probe the intergalactic turbulence. We measure the structure function (SF) of dispersion measures (DMs) of FRBs to study the multiscale electron density fluctuations induced by the intergalactic turbulence. The SF has a large amplitude and a Kolmogorov power-law scaling with angular separations, showing large and correlated DM fluctuations over a range of length scales. Given that the DMs of FRBs are IGM dominated, our result tentatively suggests that the intergalactic turbulence has a Kolmogorov power spectrum and an outer scale on the order of 100 Mpc.

Keywords: radio transient sources; intergalactic medium; hydrodynamics
Compton-thick AGN in the NuSTAR Era. IX. A Joint NuSTAR and XMM-Newton Analysis of Four Local AGN

We present the results of the broadband X-ray spectral analysis of simultaneous NuSTAR and XMM-Newton observations of four nearby Compton-thick active galactic nuclei (AGN) candidates selected from the Swift Burst Alert Telescope 150 month catalog. This work is part of a larger effort to identify and characterize all Compton-thick (N H ≥ 1024 cm-2) AGN in the local universe (z ≤ 0.05). We used three physically motivated models-MYTorus, borus02, and UXClumpy-to fit and characterize these sources. Of the four candidates analyzed, 2MASX J02051994-0233055 was found to be an unobscured (N H < 1022 cm-2) AGN, 2MASX J04075215-6116126 and IC 2227 to be Compton-thin (1022 cm-2 < N H < 1024 cm-2) AGN, and one, ESO 362-8, was confirmed to be a Compton-thick AGN. Additionally, every source was found to have a statistically significant difference between their line-of-sight and average torus hydrogen column density, further supporting the idea that the obscuring material in AGN is inhomogeneous. Furthermore, half of the sources in our sample (2MASX J02051994-0233055 and 2MASX J04075215-6116126) exhibited significant luminosity variation in the last decade, suggesting that this might be a common feature of AGN.

Keywords: active galactic nuclei; x-ray active galactic nuclei
Modeling Thermal Emission under Lunar Surface Environmental Conditions

Thermal emission spectra can provide key insights into the composition and thermophysical properties of the regolith on the Moon and other airless bodies. However, under lunar surface environmental conditions, the uppermost millimeters of the regolith (from which thermal emission originates) cannot be characterized by a single temperature, leading to changes in spectral characteristics that should be accounted for in interpreting thermal emission measurements. Here, we develop and apply a Monte Carlo radiative transfer method to model thermal emission from particulate media with varying, nonisothermal subsurface temperature profiles. We model emission spectra for three major lunar mineral phases (pyroxene, olivine, and plagioclase), and investigate the effects of particle size and packing density. Modeled spectra are compared to lab measurements acquired under both ambient and simulated lunar conditions. We find that in some cases, the model provides useful constraints on the magnitude of the temperature profile established in a lab sample under lunar-like conditions, whereas in other cases, lab spectra are not well represented by the linear temperature profiles considered in this work. The model is generally successful at predicting changes in spectral contrast under lunar-like conditions, but less successful in accurately predicting shifts in the position of the Christiansen feature emissivity maximum; we illustrate and discuss the validity of the modeling approach for a range of different cases. Model results can also be used to quantify the depth within which observed thermal emission originates; this depth depends on composition and grain size, and ranges from ~100 to 1000 μm for representative packing densities.

Keywords: the moon; spectroscopy; radiative transfer
AT2021lwx: Another Neutrino-coincident Tidal Disruption Event with a Strong Dust Echo?

We discuss the possible association of an astrophysical neutrino (IC220405B) with the recently reported, extremely energetic tidal disruption event (TDE) candidate AT2021lwx (ZTF20abrbeie, aka "Scary Barbie") at redshift z = 0.995. Although the TDE is about 2.°6 off the direction of the reconstructed neutrino event (outside the 90% confidence level localization region), the TDE candidate shares some important characteristics with so-far-reported neutrino–TDE associations: a strong infrared dust echo, high bolometric luminosity, a neutrino time delay with respect to the peak mass accretion rate of the order of a hundred days, and a high observed X-ray luminosity. We interpret this new association using an isotropic emission model, where neutrinos are produced by the collision of accelerated protons with infrared photons. After accounting for the high redshift of AT2021lwx (by interpreting the data in the supermassive black hole (SMBH) frame), we find that the expected neutrino fluences and neutrino time delays are qualitatively comparable to the other TDEs. Since data are only available up to 300 days postpeak in the SMBH frame, significant uncertainties exist in the dust echo interpretation, and therefore in the predicted number of neutrinos detected, . We recommend further follow-up of this object for an extended period and suggest refining the reconstruction of the neutrino arrival direction in this particular case.

Keywords: tidal disruption; radiative processes; neutrino astronomy; high energy astrophysics