adsabs/SciX_UAT_keywords huggingface dataset:
Lyman Continuum Emission from Spectroscopically Confirmed Lyα Emitters at z 3.1

We present a study of Lyman continuum (LyC) emission in a sample of ~150 Lyα emitters (LAEs) at z ≈ 3.1 in the Subaru-XMM Deep Survey field. These LAEs were previously selected using the narrowband technique and spectroscopically confirmed with Lyα equivalent widths (EWs) ≥ 45 Å. We obtain deep UV images using a custom intermediate-band filter U J that covers a wavelength range of 3330 ~ 3650 Å, corresponding to 810 ~ 890 Å in the rest frame. We detect five individual LyC galaxy candidates in the U J band, and their escape fractions (f esc) of LyC photons are roughly between 40% and 80%. This supports a previous finding that a small fraction of galaxies may have very high f esc. We find that the f esc values of the five LyC galaxies are not apparently correlated with other galaxy properties such as Lyα luminosity and EW, UV luminosity and slope, and star formation rate (SFR). This is partly due to the fact that these galaxies only represent a small fraction (~3%) of our LAE sample. For the remaining LAEs that are not detected in U J, we stack their U J-band images and constrain their average f esc. The upper limit of the average f esc value is about 16%, consistent with the results in the literature. Compared with the non-LyC LAEs, the LyC LAEs tend to have higher Lyα luminosities, Lyα EWs, and SFRs, but their UV continuum slopes are similar to those of other galaxies.

Keywords: high-redshift galaxies; galaxy properties; star formation
The Relation of the Alpha Persei Star Cluster with the Nearby Stellar Stream

A map of 100° on a side extracted from Gaia DR2 and centered on Alpha Persei reveals two distinct structures—the Alpha Persei star cluster and a conspicuous stellar stream, as widely documented in recent literature. In this work we employ DBSCAN to assess individual stars' membership and attempt at separating stars belonging to the cluster and to the stream from the general field. In turn, we characterize the stream and investigate its relation with the cluster. The stream population turned out to be significantly older (5 ± 1 Gyr) than the cluster, and to be positioned ∼90 pc away from the cluster, in its background. The stream exhibits a sizeable thickness of ∼180 pc in the direction of the line of view. Finally, the stream harbors a prominent population of white dwarf stars. We estimated an upper limit of the stream mass of ∼6000M⊙. The stream would therefore be the leftover of a relatively massive old cluster. The surface density map of Alpha Persei indicates the presence of tidal tails. While it is tempting to ascribe their presence to the interaction with the disrupting old star cluster, we prefer to believe, conservatively, they are of Galactic origin.

Keywords: star clusters; open star clusters; astrostatistics techniques; white dwarf stars
The Gas and Stellar Content of a Metal-poor Galaxy at z = 8.496 as Revealed by JWST and ALMA

We present a joint analysis of the galaxy S04590 at z = 8.496 based on NIRSpec, NIRCam, and NIRISS observations obtained as part of the Early Release Observations program of the James Webb Space Telescope (JWST) and the far-infrared [C II] 158 μm emission line detected by dedicated Atacama Large Millimeter/submillimeter Array (ALMA) observations. We determine the physical properties of S04590 from modeling of the spectral energy distribution (SED) and through the redshifted optical nebular emission lines detected with JWST/NIRSpec. The best-fit SED model reveals a low-mass (M ⋆ = 107.2-108 M ⊙) galaxy with a low oxygen abundance of $12+\mathrm{log}({\rm{O}}/{\rm{H}})={7.16}_{-0.12}^{+0.10}$ derived from the strong nebular and auroral emission lines. Assuming that [C II] effectively traces the interstellar medium, we estimate the total gas mass of the galaxy to be M gas = (8.0 ± 4.0) × 108 M ⊙ based on the luminosity and spatial extent of [C II]. This yields an exceptionally high gas fraction, f gas = M gas/(M gas + M ⋆) ≳ 90%, though one still consistent with the range expected for low metallicity. We further derive the metal mass of the galaxy based on the gas mass and gas-phase metallicity, which we find to be consistent with the expected metal production from Type II supernovae. Finally, we make the first constraints on the dust-to-gas (DTG) and dust-to-metal (DTM) ratios of galaxies in the epoch of reionization at z ≳ 6, showing overall low mass ratios of logDTG < -3.8 and logDTM < -0.5, though they are consistent with established scaling relations and in particular with those of the local metal-poor galaxy I Zwicky 18. Our analysis highlights the synergy between ALMA and JWST in characterizing the gas, metal, and stellar content of the first generation of galaxies.

Keywords: high-redshift galaxies; galaxies; interstellar medium; star formation; galaxy formation; galaxy evolution
Empirical Measurement of the Dynamical Ages of Three Globular Clusters and Some Considerations on the Use of the Dynamical Clock

We have used the "dynamical clock" to measure the level of dynamical evolution reached by three Galactic globular clusters (namely, NGC 3201, NGC 6316, and NGC 6440). This is an empirical method that quantifies the level of central segregation of blue straggler stars (BSSs) within the cluster half-mass radius by means of the ${A}_{\mathrm{rh}}^{+}$ parameter, defined as the area enclosed between the cumulative radial distribution of BSSs and that of a lighter population. The total sample with homogeneous determinations of ${A}_{\mathrm{rh}}^{+}$ currently includes 59 clusters: 52 old GCs in the Milky Way (including the three investigated here), five old clusters in the Large Magellanic Cloud, and two young systems in the Small Magellanic Cloud. The three objects studied here nicely nest into the correlation between ${A}_{\mathrm{rh}}^{+}$ and the central relaxation time defined by the previous sample, thus proving and consolidating the use of the dynamical clock as an excellent tracer of the stage of dynamical evolution of a star cluster in different galactic environments. Finally, we discuss the advantages of using the dynamical clock as an indicator of the dynamical ages of star clusters, compared to the present-day central relaxation time. *Based on observations collected at the Hubble Space Telescope, under proposals GO12517 (PI: Ferraro), GO13410 (PI: Pallanca), GO15232 (PI: Ferraro).

Keywords: globular star clusters; blue straggler stars; photometry
Near-infrared Polarization Charateristics of the Zodiacal Light Observed with DIRBE/COBE

We report near-infrared polarization of the zodiacal light (ZL) measured from space by the Diffuse Infrared Background Experiment (DIRBE) on board the Cosmic Background Explorer in photometric bands centered at 1.25, 2.2, and 3.5 μm. To constrain the physical properties of interplanetary dust, we use DIRBE Weekly Sky Maps to investigate the solar elongation (ϵ), ecliptic latitude (β), and wavelength (λ) dependence of ZL polarization. We find that the polarization of the ZL varies as a function of ϵ and β, consistent with observed polarization at λ = 550 nm. While the polarization dependence on wavelength at (ϵ, β) = (90°, 0°) is modest (increasing from 17.7% ± 0.2% at 1.25% μm to 21.0% ± 0.3% at 3.5 μm), the variation is more pronounced at the north ecliptic pole (23.1% ± 1.6%, 35.1% ± 2.0%, and 39.3% ± 2.1% at 1.25, 2.2, and 3.5 μm, respectively). The variation in ZL polarization with wavelength is not explained by either Rayleigh scattering or absorptive particles larger than 10 μm.

Keywords: interplanetary dust; zodiacal cloud; infrared astronomical satellite; polarimetry; near infrared astronomy
A Metallicity Dependence on the Occurrence of Core-collapse Supernovae

Core-collapse supernovae (CCSNe) are widely accepted to be caused by the explosive death of massive stars with initial masses ≳8 M ⊙. There is, however, a comparatively poor understanding of how properties of the progenitors-mass, metallicity, multiplicity, rotation, etc.-manifest in the resultant CCSN population. Here, we present a minimally biased sample of nearby CCSNe from the All-Sky Automated Survey for Supernovae survey whose host galaxies were observed with integral-field spectroscopy using MUSE at the Very Large Telescope. This data set allows us to analyze the explosion sites of CCSNe within the context of global star formation properties across the host galaxies. We show that the CCSN explosion site oxygen abundance distribution is offset to lower values than the overall H II region abundance distribution within the host galaxies. We further split the sample at $12+{\mathrm{log}}_{10}({\rm{O}}/{\rm{H}})=8.6$ dex and show that within the subsample of low-metallicity host galaxies, the CCSNe unbiasedly trace the star formation with respect to oxygen abundance, while for the subsample of higher-metallicity host galaxies, they preferentially occur in lower-abundance star-forming regions. We estimate the occurrence of CCSNe as a function of oxygen abundance per unit star formation and show that there is a strong decrease as abundance increases. Such a strong and quantified metallicity dependence on CCSN production has not been shown before. Finally, we discuss possible explanations for our result and show that each of these has strong implications not only for our understanding of CCSNe and massive star evolution but also for star formation and galaxy evolution.

Keywords: supernovae; core-collapse supernovae; stellar evolution; galaxy abundances
Revision of the γ-Ray Emission from SNR CTB 109 with the Fermi Large Area Telescope

CTB 109 is a middle-aged shell-type supernova remnant (SNR) with bright thermal X-ray emission. We reanalyze the GeV γ-ray emission from CTB 109 using 13 yr of Pass 8 data recorded by the Fermi Large Area Telescope. The γ-ray emission of CTB 109 shows a center bright morphology, which is well consistent with its thermal X-ray emission rather than the shell-type structure in the radio band. The spectral analysis shows an evident spectral curvature at ~several GeV for the GeV γ-ray spectrum, which can naturally explain the lack of TeV γ-ray emission from CTB 109. Although either a leptonic or a hadronic model could fit the multiwavelength observations of CTB 109, the hadronic model is favored considering its γ-ray morphology and the spectral curvature of the GeV spectrum. The unusual γ-ray spectrum of CTB 109 with other SNRs and the luminosity-diameter squared relation make CTB 109 distinguished both from the young-aged SNRs with hard GeV γ-ray spectra and several old-aged SNRs interacting with molecular clouds.

Keywords: supernova remnants; gamma-ray astronomy; gamma-ray sources
Soft X-Ray Excess from Shocked Black Hole Accretion

A certain class of luminous galaxies hosting supermassive black holes (BHs) is known to exhibit an excess of "soft X-rays" in their X-ray spectra. However, its physical identity and origin are yet to be understood. In this work, we systematically study a sample of 9 well-documented narrow-line Seyfert 1 active galactic nuclei by utilizing the archival XMM-Newton/EPIC spectra in the context of general relativistic magnetohydrodynamic model. In this scenario, thermal accretion disk photons (in UV) are Compton up-scattered by nonthermal energetic electrons in the hot downstream accretion due to shock compression, producing the observed soft excess. Our spectral model consists primarily of the shock Comptonization component and the underlying continuum including reflection from the accretion disk. Based on χ 2-statistics, we successfully constrain the model parameters, most notably electron energy of the downstream flow kT e , effective disk blackbody temperature kT bb, and inclination angle θ for a given BH spin. The disk temperature is commonly found to be kT bb 10 eV and the electron energy ranges from kT e 75-160 keV (for Schwarzschild BHs) to 126-232 keV (for Kerr BHs) depending on inclination. Our analyses imply that the characteristics of the observed soft excess are strongly dependent on the properties of the downstream accretion flow and BH spin.

Keywords: x-ray astronomy; x-ray active galactic nuclei; active galactic nuclei
Linking Outer Disk Pebble Dynamics and Gaps to Inner Disk Water Enrichment

Millimeter continuum imaging of protoplanetary disks reveals the distribution of solid particles and the presence of substructures (gaps and rings) beyond 5-10 au, while infrared (IR) spectra provide access to abundances of gaseous species at smaller disk radii. Building on recent observational findings of an anti-correlation between the inner disk water luminosity and outer dust disk radius, we aim here at investigating the dynamics of icy solids that drift from the outer disk and sublimate their ice inside the snow line, enriching the water vapor that is observed in the IR. We use a volatile-inclusive disk evolution model to explore a range of conditions (gap location, particle size, disk mass, and α viscosity) under which gaps in the outer disk efficiently block the inward drift of icy solids. We find that inner disk vapor enrichment is highly sensitive to the location of a disk gap, yielding for each particle size a radial "sweet spot" that reduces the inner disk vapor enrichment to a minimum. For pebbles of 1-10 mm in size, which carry the most mass, this sweet spot is at 7-15 au, suggesting that inner gaps may have a key role in reducing ice delivery to the inner disk and may not allow the formation of Earths and super-Earths. This highlights the importance of observationally determining the presence and properties of inner gaps in disks. Finally, we argue that the inner water vapor abundance can be used as a proxy for estimating the pebble drift efficiency and mass flux entering the inner disk.

Keywords: protoplanetary disks; planet formation; exoplanets
Overfitting Affects the Reliability of Radial Velocity Mass Estimates of the V1298 Tau Planets

Mass, radius, and age measurements of young (≲100 Myr) planets have the power to shape our understanding of planet formation. However, young stars tend to be extremely variable in both photometry and radial velocity (RV) measurements, which makes constraining these properties challenging. The V1298 Tau system of four ~0.5 R J planets transiting a pre-main-sequence star presents an important, if stress-inducing, opportunity to observe and measure directly the properties of infant planets. Suárez Mascareño et al. published radial-velocity-derived masses for two of the V1298 Tau planets using a state-of-the-art Gaussian process regression framework. The planetary densities computed from these masses were surprisingly high, implying extremely rapid contraction after formation in tension with most existing planet-formation theories. In an effort to constrain further the masses of the V1298 Tau planets, we obtained 36 RVs using Keck/HIRES, and analyzed them in concert with published RVs and photometry. Through performing a suite of cross-validation tests, we found evidence that the preferred model of Suárez Mascareño et al. suffers from overfitting, defined as the inability to predict unseen data, rendering the masses unreliable. We detail several potential causes of this overfitting, many of which may be important for other RV analyses of other active stars, and recommend that additional time and resources be allocated to understanding and mitigating activity in active young stars such as V1298 Tau.

Keywords: starspots; radial velocity
The Evolution of Population III and Extremely Metal-poor Binary Stars

Numerical simulations have now shown that Population III (Pop III) stars can form in binaries and small clusters and that these stars can be in close proximity to each other. If so, they could be subject to binary interactions such as mass exchange that could profoundly alter their evolution, ionizing UV and Lyman-Werner photon emission and explosion yields, with important consequences for early cosmological reionization and chemical enrichment. Here we investigate the evolution of Pop III and extremely metal-poor binary stars with the MESA code. We find that interactions ranging from stable mass transfer to common envelope evolution can occur in these binaries for a wide range of mass ratios and initial separations. Mass transfer can nearly double UV photon yields in some of these binaries with respect to their individual stars by extending the life of the companion star, which in turn can enhance early cosmological reionization but also suppress the formation of later generations of primordial stars. Binary interactions can also have large effects on the nucleosynthetic yields of the stars by promoting or removing them into or out of mass ranges for specific SN types. We provide fits to total photon yields for the binaries in our study for use in cosmological simulations.

Keywords: binary stars; close binary stars; stellar evolutionary models; stellar evolution; population iii stars; stellar feedback
Long-term Evolution in Ionization of Ejecta Illuminated by Eta Carinae

Changes in the flux and spectrum of Eta Carinae (η Car) since 1900 have been attributed to the evolution of the central binary by some. Others suggest evolution in the occulting ejecta. The brightness jump in the 1940s, which coincided with the appearance of narrow forbidden emission lines, may have been caused by the clearing and ionization of intervening circumstellar ejecta. The brightening changed at a slower pace up through 40 yr later. Here we continue earlier studies focused on the long-term, showing that the forbidden line emission increased in the early 1990s with no noticeable increase in the brightness of the Homunculus. We interpret that the increase in narrow-line emission is due to decreased extinction in the line of sight (LOS) from the central binary to the Weigelt clumps. In 2000, the central stellar core increased in brightness at a faster rate without associated changes in the Homunculus. By 2018, hundreds of narrow-line absorptions from singly ionized metals in our LOS from (η Car) disappeared, thought to be caused by increased ionization of metals. These three events (1990, 2000, and 2018) are explained by the dissipation of circumstellar material within the Homunculus close to the binary. Combining these changes with the steadiness of the Homunculus and the primary winds over the past four decades indicates that circumstellar ejecta in our direction have been cleared.

Keywords: massive stars
Alternative Waiting Time Statistics for the Lu and Hamilton Avalanche Model

The solar corona hosts many explosive events. Among them, flares are some of the most energetic, rapidly releasing huge amounts of energy and, in the case of the largest ones, producing coronal mass ejections that have the potential to harm life on our planet. Therefore, there is great interest in attempting to foresee the occurrence of extreme solar flares. Avalanche models for solar flares have been used since the beginning of the 1990s to model the flaring corona in a simple and computationally inexpensive way. The pioneering and now most prevalent model in the literature was proposed by Lu and Hamilton. This model has been extremely useful to reproduce most of the main characteristic features observed in solar flares (e.g., the probability density function of a flare's energy) and, in recent years, has been used as the starting point to predict extreme flaring events. In this work, we revisit Lu and Hamilton's model and the very definition of waiting time for both extreme and all-sized events. We find that extreme avalanche statistics are well described by a log-normal distribution, in accordance with recent observations of solar flares.

Keywords: solar flares; solar corona
Ab Initio Study of Glycine Formation in the Condensed Phase: Carbon Monoxide, Formaldimine, and Water Are Enough

Glycine is considered to be crucial in the formation of proteins and prebiotic substances. Nevertheless, the mechanism of spontaneous glycine formation under prebiotic Earth conditions or within the interstellar medium (ISM) remains a topic of debate, given the changing geochemical environment over Earth's history and the difficulty of detecting it within the ISM. Yet it is believed that its formation could be possible in interstellar water-rich ice. In this study, using molecular dynamics (MD) simulations at the ab initio level of theory enhanced with modern free energy calculations, we modeled the chemical reaction between carbon monoxide, formaldimine, and water to produce glycine. We estimated under what conditions, in condensed phase at 50, 70, 100, and 300 K, glycine is formed. We also explored the effect of different electric fields on this process. Our results show that glycine could be formed with energy barriers as low as 0.5 kcal mol-1 at 50 K. We discuss whether this reaction could be a suitable candidate for explaining the mechanism of glycine formation under conditions that resemble various astrophysical environments, such as planets, exoplanets, and Earth. This study is relevant to finding a consensus among various proposals for glycine formation. Moreover, it highlights the importance of metadynamics and Car-Parrinello MD methods as tools in finding unknown complex, multistep reaction mechanism pathways, possibly important to the astronomical phenomena.

Keywords: pre-biotic astrochemistry; interstellar medium; molecular reactions; astrobiology; interstellar molecules
CLASS Angular Power Spectra and Map-component Analysis for 40 GHz Observations through 2022

Measurement of the largest angular scale (ℓ < 30) features of the cosmic microwave background (CMB) polarization is a powerful way to constrain the optical depth to reionization and search for the signature of inflation through the detection of primordial B-modes. We present an analysis of maps covering 73.6% of the sky made from the 40 GHz channel of the Cosmology Large Angular Scale Surveyor (CLASS) from 2016 August to 2022 May. Taking advantage of the measurement stability enabled by front-end polarization modulation and excellent conditions from the Atacama Desert, we show this channel achieves higher sensitivity than the analogous frequencies from satellite measurements in the range 10 < ℓ < 100. Simulations show the CLASS linear (circular) polarization maps have a white noise level of $125(130)\,\mu {\rm{K}}\,\mathrm{arcmin}$ . We measure the Galaxy-masked EE and BB spectra of diffuse synchrotron radiation and compare to space-based measurements at similar frequencies. In combination with external data, we expand measurements of the spatial variations of the synchrotron spectral energy density (SED) to include new sky regions and measure the diffuse SED in the harmonic domain. We place a new upper limit on a background of circular polarization in the range 5 < ℓ < 125 with the first bin showing D ℓ < 0.023 $\mu {{\rm{K}}}_{\mathrm{CMB}}^{2}$ at 95% confidence. These results establish a new standard for recovery of the largest-scale CMB polarization from the ground and signal exciting possibilities when the higher sensitivity and higher-frequency CLASS channels are included in the analysis.

Keywords: early universe; cosmic microwave background radiation; observational cosmology; astronomy data analysis; polarimeters