adsabs/SciX_UAT_keywords huggingface dataset:
Searching for Islands of Reionization: A Potential Ionized Bubble Powered by a Spectroscopic Overdensity at z = 8.7

We present the results from a spectroscopic survey using the MOSFIRE near-infrared spectrograph on the 10 m Keck telescope to search for Lyα emission from candidate galaxies at z ~ 9-10 in four of the CANDELS fields (GOODS-N, EGS, UDS, and COSMOS). We observed 11 target galaxies, detecting Lyα from one object in ~8.1 hr of integration, at z = 8.665 ± 0.001 with an integrated signal-to-noise ratio > 7. This galaxy is in the CANDELS Extended Groth Strip (EGS) field and lies physically close (3.5 physical Mpc [pMpc]) to another confirmed galaxy in this field with Lyα detected at z = 8.683. The detection of Lyα suggests the existence of large (~1 pMpc) ionized bubbles fairly early in the reionization process. We explore the ionizing output needed to create bubbles of this size at this epoch and find that such a bubble requires more than the ionizing power provided by the full expected population of galaxies (by integrating the UV luminosity function down to M UV = -13). The Lyα we detect would be able to escape the predominantly neutral intergalactic medium at this epoch if our detected galaxy is inhabiting an overdensity, which would be consistent with the photometric overdensity previously identified in this region by Finkelstein et al. This implies that the CANDELS EGS field is hosting an overdensity at z = 8.7 that is powering one or more ionized bubbles, a hypothesis that will be imminently testable with forthcoming James Webb Space Telescope observations in this field.

Keywords: high-redshift galaxies; lyman-alpha galaxies; reionization; galaxy spectroscopy; spectroscopy; high-redshift galaxy clusters
A New Facility for Airborne Solar Astronomy: NASA's WB-57 at the 2017 Total Solar Eclipse

NASA's WB-57 High Altitude Research Program provides a deployable, mobile, and stratospheric platform for scientific research. Airborne platforms are of particular value for making coronal observations during total solar eclipses because of their ability both to follow the Moon's shadow and to get above most of the atmospheric air mass that can interfere with astronomical observations. We used the 2017 August 21 eclipse as a pathfinding mission for high-altitude airborne solar astronomy, using the existing high-speed visible-light and near/midwave infrared imaging suite mounted in the WB-57 nose cone. In this paper, we describe the aircraft, the instrument, and the 2017 mission; operations and data acquisition; and preliminary analysis of data quality from the existing instrument suite. We describe benefits and technical limitations of this platform for solar and other astronomical observations. We present a preliminary analysis of the visible-light data quality and discuss the limiting factors that must be overcome with future instrumentation. We conclude with a discussion of lessons learned from this pathfinding mission and prospects for future research at upcoming eclipses, as well as an evaluation of the capabilities of the WB-57 platform for future solar astronomy and general astronomical observation.

Keywords: solar eclipses; total eclipses; solar corona; solar coronal heating; solar coronal plumes; solar coronal streamers; solar coronal waves; solar instruments; the sun; astronomical instrumentation
A Magnetar-asteroid Impact Model for FRB 200428 Associated with an X-Ray Burst from SGR 1935+2154

Very recently, an extremely bright fast radio burst (FRB) 200428 with two submillisecond pulses was discovered coming from the direction of the Galactic magnetar SGR 1935+2154, and an X-ray burst (XRB) counterpart was detected simultaneously. These observations favor magnetar-based interior-driven models. In this Letter, we propose a different model for FRB 200428 associated with an XRB from SGR 1935+2154 in which a magnetar with high proper velocity encounters an asteroid of mass ∼1020 g. This infalling asteroid in the stellar gravitational field is first possibly disrupted tidally into a great number of fragments at a radius of ∼a few times 1010 cm, and then slowed around the Alfvén radius by an ultra-strong magnetic field, and in the meantime two major fragments of mass ∼1017 g that cross magnetic field lines produce two pulses of FRB 200428. The whole asteroid is eventually accreted onto the poles along magnetic field lines, impacting the stellar surface, creating a photon-e± pair fireball trapped initially in the stellar magnetosphere, and further leading to an XRB. We show that this gravitationally powered model can interpret all of the observed features self-consistently.

Keywords: radio bursts; asteroids; soft gamma-ray repeaters; magnetars
Chandra Detection of Three X-Ray Bright Quasars at z > 5

We report Chandra detection of three UV-bright radio-quiet quasars at z ≳ 5. We have collected a sufficient number of photons to extract an X-ray spectrum of each quasar to measure their basic X-ray properties, such as the X-ray flux, power-law photon index (Γ), and optical-to-X-ray spectral slope (αOX). J074749+115352 at z = 5.26 is the X-ray brightest radio-quiet quasar at z > 5. It may have a short timescale variation (on a timescale of ∼3800 s in the observer's frame, or ∼600 s in the rest frame), which is, however, largely embedded in the statistical noise. We extract phase folded spectra of this quasar. There are two distinguishable states: a "high soft" state with an average X-ray flux ∼2.7 times the "low hard" state, and a significantly steeper X-ray spectral slope ( ${\rm{\Gamma }}={2.40}_{-0.32}^{+0.33}$ versus ${1.78}_{-0.24}^{+0.25}$ ). We also compare the three quasars detected in this paper to other quasar samples. We find that J074749+115352, with an SMBH mass of MSMBH ≈ 1.8 × 109 M⊙ and an Eddington ratio of λEdd ≈ 2.3, is extraordinarily X-ray bright. It has an average αOX = -1.46 ± 0.02 and a 2-10 keV bolometric correction factor of Lbol/L2-10 keV = 42.4 ± 5.8, both significantly depart from some well defined scaling relations. We compare Γ of the three quasars to other samples at different redshifts, and do not find any significant redshift evolution based on the limited sample of z > 5 quasars with reliable measurements of the X-ray spectral properties.

Keywords: x-ray quasars; high-redshift galaxies; early universe; supermassive black holes
A Rest-frame Near-IR Study of Clumps in Galaxies at 1 < z < 2 Using JWST/NIRCam: Connection to Galaxy Bulges

A key question in galaxy evolution has been the importance of the apparent "clumpiness" of high-redshift galaxies. Until now, this property has been primarily investigated in rest-frame UV, limiting our understanding of their relevance. Are they short-lived or are they associated with more long-lived massive structures that are part of the underlying stellar disks? We use JWST/NIRCam imaging from the Cosmic Evolution and Epoch of Reionization Survey to explore the connection between the presence of these "clumps" in a galaxy and its overall stellar morphology, in a mass-complete ( $\mathrm{log}\,{M}_{* }/{M}_{\odot }\gt 10.0$ ) sample of galaxies at 1.0 < z < 2.0. Exploiting the uninterrupted access to rest-frame optical and near-IR light, we simultaneously map the clumps in galactic disks across our wavelength coverage, along with measuring the distribution of stars among their bulges and disks. First, we find that the clumps are not limited to the rest-frame UV and optical, but are also apparent in near-IR with ~60% spatial overlap. This rest-frame near-IR detection indicates that clumps would also feature in the stellar-mass distribution of the galaxy. A secondary consequence is that these will hence be expected to increase the dynamical friction within galactic disks leading to gas inflow. We find a strong negative correlation between how clumpy a galaxy is and strength of the bulge. This firmly suggests an evolutionary connection, either through clumps driving bulge growth or the bulge stabilizing the galaxy against clump formation, or a combination of the two. Finally, we find evidence of this correlation differing from rest-frame optical to near-IR, which could suggest a combination of varying formation modes for the clumps.

Keywords: galaxy evolution; galaxy structure; galaxy formation
Modeling Evolution of Galactic Bars at Cosmic Dawn

We study the evolution of galactic bars using a suite of very high-resolution zoom-in cosmological simulations of galaxies at z ~ 9-2. Our models were chosen to lie within similar-mass dark matter (DM) halos, log(M vir/M ⊙) ~ 11.65 ± 0.05, at z = 6, 4, and 2, in high- and low-overdensity environments. We apply two galactic wind feedback mechanisms for each model. All galaxies develop subkiloparsec stellar bars differing in their properties. We find that (1) the high-z bars form in response to various perturbations: mergers, close flybys, cold accretion inflows along the cosmological filaments, etc.; (2) these bars account for the large mass fraction of galaxies; (3) bars display large corotation-to-bar size ratios, are weaker compared to their low-redshift counterparts by measuring their Fourier amplitudes, and are very gas-rich; (4) their pattern speed does not exhibit monotonic decline with time owing to braking against DM, as at low z; (5) bar properties, including their stellar population (star formation rates and metal enrichment), depend sensitively on prevailing feedback; and (6) bars can weaken substantially during cosmological evolution, becoming weak oval distortions-hence bars are destroyed and reformed multiple times, unlike their low-z counterparts. In all cases, bars in our simulations have been triggered by interactions. In summary, not only do stellar bars appear to be a contemporary phenomenon, but based on increased frequency of mergers, flybys, and the strength of cold accretion flows at high z, we also expect them to be ubiquitous at redshifts ≳2-the epoch of rapid galaxy growth and larger stellar dispersion velocities.

Keywords: galactic abundances; barred spiral galaxies; hydrodynamical simulations; high-redshift galaxies; galaxy evolution; galaxy interactions
Ion and Electron Acceleration in Fully Kinetic Plasma Turbulence

Turbulence is often invoked to explain the origin of nonthermal particles in space and astrophysical plasmas. By means of 3D fully kinetic particle-in-cell simulations, we demonstrate that turbulence in low-β plasmas (β is the ratio of plasma pressure to magnetic pressure) accelerates ions and electrons into a nonthermal energy distribution with a power-law energy range. The ion spectrum is harder than the electron one, and both distributions get steeper for higher β. We show that the energization of electrons is accompanied by a significant energy-dependent pitch-angle anisotropy, with most electrons moving parallel to the local magnetic field, while ions stay roughly isotropic. We demonstrate that particle injection from the thermal pool occurs in regions of high current density. Parallel electric fields associated with magnetic reconnection are responsible for the initial energy gain of electrons, whereas perpendicular electric fields control the overall energization of ions. Our findings have important implications for the origin of nonthermal particles in space and astrophysical plasmas.

Keywords: high energy astrophysics; plasma astrophysics
Spectral Properties of the Soft X-Ray Transient MAXI J0637-430 Using AstroSat

Soft X-ray transients are systems that are detected when they go into an outburst, wherein their X-ray luminosity increases by several orders of magnitude. These outbursts are markers of the poorly understood change in the spectral state of these systems from the low/hard state to the high/soft state. We report the spectral properties of one such soft X-ray transient: MAXI J0637-430, with data from the SXT and LAXPC instruments on board the AstroSat mission. The source was observed for a total of ~60 ks in two observations on 2019 November 8 and 21 soon after its discovery. Flux-resolved spectral analysis of the source indicates the presence of a multicolor blackbody component arising from the accretion disk and a thermal Comptonization component. The stable low temperature (~0.55 keV) of the blackbody component points to a cool accretion disk with an inner disk radius of the order of a few hundred kilometers. In addition, we report the presence of a relativistically broadened Gaussian line at 6.4 keV. The disk-dominated flux and photon power-law index of ⪆2 and a constant inner disk radius indicate the source to be in the soft state. From the study we conclude that MAXI J0637-430 is a strong candidate for a black hole X-ray binary.

Keywords: low-mass x-ray binary stars
A Nitrogen-rich Supernova Remnant in M31: Interaction with the Circumstellar Medium at Late Times

We present the discovery of a supernova remnant in M31 which is unlike any other remnant known in that galaxy. An optical ground-based spectrum of WB92-26 taken at the MMT and sampling most of this marginally resolved object reveals strong lines of [O II], [Ne III], H I, [O III], [O I], [N II] and [S II], though the H I lines are very weak and the [N II] lines are very strong. Multiple velocity components are visible in those lines, with broad wings extending to -2000 and +1500 or 2000 km s-1 (the heliocentric velocity of M31 is -300 km s-1). The lines show strong peaks or shoulders near -750, -50, and +800 km s-1 in the M31 frame. The density implied by the [S II] ratio combined with the X-ray luminosity, FUV flux, and optical size lead us to conclude that the optical emission lines are generated by shock waves, not photoionization. Consideration of the velocity structure indicates that the emission is from a shock in the circumstellar medium (CSM). This CSM must be depleted in hydrogen and enriched in helium and nitrogen through CNO processing, and it must have had a high velocity before the explosion of the parent star, to explain the broad wings in the emission lines. We estimate the CSM shell to have a mass of 2 M ⊙, implying a core-collapse SN. It is likely that Eta Car will produce a remnant resembling WB92-26 a few thousand years after it explodes.

Keywords: supernova remnants; andromeda galaxy; circumstellar matter; galaxy spectroscopy
The Universe is at Most 88% Neutral at z = 10.6

Recent observations of GN-z11 with JWST have revealed a Lyα emission line with an equivalent width (EW) of 18 ± 2 Å. At z = 10.6, this galaxy is expected to lie in the heart of reionization. We use a series of inhomogeneous reionization simulations to derive the distribution of the Lyα EW after traveling through the neutral intergalactic medium with varying average neutral gas fraction, x H I. We use these distributions to place an upper limit of x H I < 0.88 at z = 10.6 at 95% confidence level. We compare our upper limit to different reionization history models, which include the recently identified enhancement at the bright end of the luminosity function at z > 8. We find that models in which faint galaxies have a higher escape fraction compared to bright galaxies are favored by the new data.

Keywords: reionization; high-redshift galaxies
EstrellaNueva: An Open-source Software to Study the Interactions and Detection of Neutrinos Emitted by Supernovae

Supernovae emit large fluxes of neutrinos, which can be detected by detectors on Earth. Future multi-kiloton scale detectors will be sensitive to several neutrino interaction channels, with thousands of events expected if a supernova emerges in the galaxy neighborhood. There are a limited number of tools to study the interaction rates of supernova neutrinos, although a plethora of available supernova models exist. EstrellaNueva is an open-source software to calculate expected rates of supernova neutrinos in detectors using target materials with typical compositions, and additional compositions can be easily added. This software considers the flavor transformation of neutrinos in the supernova through the adiabatic Mikheyev-Smirnov-Wolfenstein effect, and their interaction in detectors through several channels. Most of the interaction cross sections, such as neutrino-electron and neutrino-proton elastic scattering, inverse beta decay, and coherent elastic neutrino-nucleus scattering, have been analytically implemented. This software provides a link between supernova simulations and the expected events in detectors by calculating fluences and event rates in order to ease any comparison between theory and observation. It provides a simple and standalone tool to explore many physics scenarios, offering an option to add analytical cross sections and define any target material.

Keywords: supernova neutrinos
High-resolution Spectroscopic Analysis of Four Unevolved Barium Stars

A classical local thermodynamic equilibrium analysis, based on high-resolution spectroscopic data, is performed for a sample of three potential barium dwarf candidates and one star already recognized as such. We derived their atmospheric parameters, estimated their masses and luminosities, and determined chemical abundances for a set of 21 elements, including CNO. Some elemental abundances are derived for the first time in HD 15096, HD 37792, and HD 141804. The program stars are dwarfs/subgiants with metallicities typical of disk stars, exhibiting moderate carbon enhancements, with [C/Fe] ratios ranging from +0.29 to +0.66 dex, and high levels of slow neutron-capture (s-process) elements, with [s/Fe] ≳ + 1.0 dex. As spectroscopic binaries, their peculiarities are attributable to mass transfer events. The observed neutron-capture patterns of were individually compared with two sets of s-process nucleosynthesis models (Monash and FRUITY), yielding dilution factors and masses estimates for the former polluting asymptotic giant branch stars. Low-mass (≲3.0 M ⊙) models successfully reproduce the observations. In addition, we estimated mean neutron exposures on the order of 0.6–0.7 mb‑1 for the s-processed material observed in their envelopes. Applying an empirical initial-final mass relation, we constraint in ∼0.7 M ⊙ the mass of their dim white dwarf companions. Moreover, our kinematic study revealed that the program stars are members of the thin disk, with probabilities greater than 70%. Hence, we identified HD 15096 and HD 37792 as new barium dwarfs and confirmed that HD 141804 is a barium dwarf. Thus, the number of barium dwarfs identified in the literature from high-resolution spectroscopy increases to 71 objects. * HD 15096, HD 37792, and HD 141804 were observed under the program ID 097.A-9024(A). HD 207585 was observed under the agreement between Observatório Nacional (Brazil) and the European Southern Observatory (ESO).

Keywords: fundamental parameters of stars; stellar atmospheres; stellar abundances; chemically peculiar stars; spectroscopy
Mid-to-late M Dwarfs Lack Jupiter Analogs

Cold Jovian planets play an important role in sculpting the dynamical environment in which inner terrestrial planets form. The core accretion model predicts that giant planets cannot form around low-mass M dwarfs, although this idea has been challenged by recent planet discoveries. Here, we investigate the occurrence rate of giant planets around low-mass (0.1-0.3 M ⊙) M dwarfs. We monitor a volume-complete, inactive sample of 200 such stars located within 15 pc, collecting four high-resolution spectra of each M dwarf over six years and performing intensive follow-up monitoring of two candidate radial velocity variables. We use TRES on the 1.5 m telescope at the Fred Lawrence Whipple Observatory and CHIRON on the Cerro Tololo Inter-American Observatory 1.5 m telescope for our primary campaign, and MAROON-X on Gemini-North for high-precision follow up. We place a 95% confidence upper limit of 1.5% (68% confidence limit of 0.57%) on the occurrence of M P sin i > 1 M J giant planets out to the water snow line and provide additional constraints on the giant planet population as a function of M P sin i and period. Beyond the snow line (100 K < T eq < 150 K), we place 95% confidence upper limits of 1.5%, 1.7%, and 4.4% (68% confidence limits of 0.58%, 0.66%, and 1.7%) for 3 M J < M P sin i < 10 M J, 0.8 M J < M P sin i < 3 M J, and 0.3 M J < M P sin i < 0.8 M J giant planets, respectively; i.e., Jupiter analogs are rare around low-mass M dwarfs. In contrast, surveys of Sun-like stars have found that their giant planets are most common at these Jupiter-like instellations.

Keywords: extrasolar gaseous giant planets; m dwarf stars; radial velocity; surveys; high resolution spectroscopy
Triggering a Climate Change Dominated "Anthropocene": Is It Common among Exocivilizations?

We seek to model the coupled evolution of a civilization and its host planet through the era when energy harvesting by the civilization drives the planet into new and adverse climate states. In this way, we ask if triggering "Anthropocenes" of the kind humanity is experiencing might be a generic feature of planet-civilization evolution. This question has direct consequences for both the study of astrobiology and the sustainability of human civilization. Furthermore, if Anthropocenes prove fatal for some civilizations then they can be considered as one form of a "Great Filter" and are therefore relevant to discussions of the Fermi Paradox. In this study, we focus on the effects of energy harvesting via combustion and vary the planet's initial chemistry and orbital radius. We find that in this context, the most influential parameter dictating a civilization's fate is their host planet's climate sensitivity, which quantifies how global temperatures change as CO2 is added to the atmosphere. Furthermore, this is in itself a function of the planet's atmospheric CO2 level, so planets with low levels of CO2 will have high climate sensitivities and high probabilities of triggering climate change. Using simulations of the coupled nonlinear model combined with semi-analytic treatments, we find that most planets in our initial parameter space experience diminished growth due to climate effects, an event we call a "climate-dominated Anthropocene."

Keywords: astrobiology; exoplanets; planetary climates
Global Structure and Dominant Particle Acceleration Mechanism of the Heliosheath: Definitive Conclusions

During its exploration of the heliosheath, the region that lies between the termination shock of the solar wind and the heliopause that separates the solar wind from the local interstellar medium, the Voyager 1 spacecraft (V1) in 2012 encountered an apparent boundary where there was a precipitous decrease in energetic particles accelerated in the heliosheath, the so-called anomalous cosmic rays (ACRs), and from the occasional plasma density measurements on V1, a density comparable to the expected density in the interstellar medium. In 2013, the Voyager principal investigators announced that this apparent boundary was the heliopause and that V1 had entered the interstellar medium. In 2014, Fisk & Gloeckler presented a detailed model that demonstrated that the apparent boundary was simply an internal surface within the heliosheath, across which compressed solar wind flows and will continue to flow until it encounters the actual heliopause. There is compelling observational evidence that the model of Fisk & Gloeckler for the nose region of the heliosheath is correct: V1 did not cross the heliopause in 2012 and is not now in the interstellar medium. There is also compelling observational evidence that the ACRs are accelerated in the heliosheath by the pump acceleration mechanism of Fisk & Gloeckler. The success of the models of Fisk & Gloeckler confirms that the plasma in the nose region of the heliosheath consists of two separate components, the pickup ions and ACRs, and the thermal solar wind, and as a unique plasma is worthy of more study and, if possible, more exploration.

Keywords: heliosphere; heliopause; heliosheath; termination shock