adsabs/SciX_UAT_keywords huggingface dataset:
Identification of Galaxy Protoclusters Based on the Spherical Top-hat Collapse Theory

We propose a new method for finding galaxy protoclusters that is motivated by structure formation theory and also directly applicable to observations. We adopt the conventional definition that a protocluster is a galaxy group whose virial mass M vir < M cl at its epoch, where M cl = 1014 M ⊙, but would exceed that limit when it evolves to z = 0. We use the critical overdensity for complete collapse at z = 0 predicted by the spherical top-hat collapse model to find the radius and total mass of the regions that would collapse at z = 0. If the mass of a region centered at a massive galaxy exceeds M cl, the galaxy is at the center of a protocluster. We define the outer boundary of a protocluster as the zero-velocity surface at the turnaround radius so that the member galaxies are those sharing the same protocluster environment and showing some conformity in physical properties. We use the cosmological hydrodynamical simulation Horizon Run 5 (HR5) to calibrate this prescription and demonstrate its performance. We find that the protocluster identification method suggested in this study is quite successful. Its application to the high-redshift HR5 galaxies shows a tight correlation between the mass within the protocluster regions identified according to the spherical collapse model and the final mass to be found within the clusters at z = 0, meaning that the regions can be regarded as the bona fide protoclusters with high reliability. We also confirm that the redshift-space distortion does not significantly affect the performance of the protocluster identification scheme.

Keywords: galaxy kinematics; galaxies; galaxy evolution; high-redshift galaxy clusters; galaxy dynamics; galaxy formation
Relating the Structure of Dark Matter Halos to Their Assembly and Environment

We use a large N-body simulation to study the relation of the structural properties of dark matter halos to their assembly history and environment. The complexity of individual halo assembly histories can be well described by a small number of principal components (PCs), which, compared to formation times, provide a more complete description of halo assembly histories and have a stronger correlation with halo structural properties. Using decision trees built with the random ensemble method, we find that about 60%, 10%, and 20% of the variances in halo concentration, axis ratio, and spin, respectively, can be explained by combining four dominating predictors: the first PC of the assembly history, halo mass, and two environment parameters. Halo concentration is dominated by halo assembly. The local environment is found to be important for the axis ratio and spin but is degenerate with halo assembly. The small percentages of the variance in the axis ratio and spin that are explained by known assembly and environmental factors suggest that the variance is produced by many nuanced factors and should be modeled as such. The relations between halo intrinsic properties and environment are weak compared to their variances, with the anisotropy of the local tidal field having the strongest correlation with halo properties. Our method of dimension reduction and regression can help simplify the characterization of the halo population and clarify the degeneracy among halo properties.

Keywords: galaxy dark matter halos
Extinction of Taurus, Orion, Perseus, and California Molecular Clouds Based on the LAMOST, 2MASS, and Gaia Surveys. I. 3D Extinction and Structure

The 3D extinction and structure are studied for the Taurus, Orion, Perseus, and California molecular clouds based on the LAMOST spectroscopy. Stellar color excess is calculated with the intrinsic color index derived from the atmospheric parameters in the LAMOST DR8 catalog and the observed color index in the Gaia EDR3 and the 2MASS PSC. In combination with the distance from the Gaia EDR3 parallax, the 3D dust extinction maps are retrieved in the color excesses ${E}_{{{\rm{G}}}_{\mathrm{BP}},{{\rm{G}}}_{\mathrm{RP}}}$ and ${E}_{{\rm{J}},{{\rm{K}}}_{{\rm{S}}}}$ with an uncertainty of ~0.03 mag and ~0.07 mag respectively. The extinction maps successfully separate the clouds that overlap in the sky area and manifest the structure of the individual cloud. Meanwhile, a bow-like structure is found with a distance range from 175 to 250 pc, half of which is a part of the Per-Tau Shell in similar coordinates and distance while the other half is not. Three low-extinction rings are additionally discovered and briefly discussed.

Keywords: molecular clouds; interstellar dust extinction; extinction; interstellar dust; distance measure
Satellite Constellation Internet Affordability and Need

Large satellite constellations in low-Earth orbit seek to be the infrastructure for global broadband Internet and other telecommunication needs. We briefly review the impacts of satellite constellations on astronomy and show that the Internet service offered by these satellites will primarily target populations where it is unaffordable, not needed, or both. The harm done by tens to hundreds of thousands of low-Earth orbit satellites to astronomy, stargazers worldwide, and the environment is not acceptable.

Keywords: artificial satellites
Asphericity of the Base of the Solar Convection Zone

We have used solar oscillation frequencies and frequency splittings obtained over solar cycles 23 and 24 to investigate whether the base of the solar convection zone shows any departure from spherical symmetry. We used the even-order splitting coefficients, a 2–a 8, and estimated the contributions from each one separately. The average asphericity over the two solar cycles was determined using frequencies and splittings obtained with a 9216-day time series. We find that evidence of asphericity is, at best, marginal: the a 2 component is consistent with no asphericity, the a 4 and a 6 components yield results at a level a little greater than 1σ, while the a 8 component shows a signature below 1σ. The combined results indicate that the time average of the departure from the spherically symmetric position of the base of the convection zone is ≲0.0001R ⊙. We have also used helioseismic data obtained from time series of lengths of 360, 576, 1152, and 2304 days in order to examine the consistency of the results and evaluate whether there is any time variation. We find that the evidence for time variation is statistically marginal in all cases, except for the a 6 component, for which tests consistently yield p-values of less than 0.05.

Keywords: the sun; helioseismology; solar interior; solar convective zone; solar cycle
Visual Orbits of Spectroscopic Binaries with the CHARA Array. IV. HD 61859, HD 89822, HD 109510, and HD 191692

We present the visual orbits of four spectroscopic binary stars, HD 61859, HD 89822, HD 109510, and HD 191692, using long baseline interferometry with the CHARA Array. We also obtained new radial velocities from echelle spectra using the APO 3.5 m, CTIO 1.5 m, and Fairborn Observatory 2.0 m telescopes. By combining the astrometric and spectroscopic observations, we solve for the full, three-dimensional orbits and determine the stellar masses to 1%-12% uncertainty and distances to 0.4%-6% uncertainty. We then estimate the effective temperature and radius of each component star through Doppler tomography and spectral energy distribution analyses. We found masses of 1.4-3.5 M ⊙, radii of 1.5-4.7 R ⊙, and temperatures of 6400-10,300 K. We then compare the observed stellar parameters to the predictions of the stellar evolution models, but found that only one of our systems fits well with the evolutionary models.

Keywords: binary stars; spectroscopic binary stars; visual binary stars; long baseline interferometry; fundamental parameters of stars
Revised Analysis of Fe VII

New spectrograms of multiply ionized iron have been recorded and analyzed, targeting the Fe VII spectrum. As a result, several previously unknown spectral lines and energy levels have been identified in this spectrum. These new data have been analyzed together with all previously published laboratory and astrophysical data on this spectrum. The energy levels have been interpreted using parametric calculations with Cowan codes. Radiative transition rates calculated in this work supplemented other previously published calculations in constructing a complete set of recommended transition probabilities. The ionization energy of Fe VII has been redetermined with a fivefold improvement in accuracy. Its new value is 1,007,928(20) cm-1, corresponding to 124.9671(25) eV.

Keywords: atomic spectroscopy; spectroscopy; line intensities; solar extreme ultraviolet emission; solar transition region
Solar Flare Heating with Turbulent Suppression of Thermal Conduction

During solar flares, plasma is typically heated to very high temperatures, and the resulting redistribution of energy via thermal conduction is a primary mechanism transporting energy throughout the flaring solar atmosphere. The thermal flux is usually modeled using Spitzer's theory, which is based on local Coulomb collisions between the electrons carrying the thermal flux and those in the background. However, often during flares, temperature gradients become sufficiently steep that the collisional mean free path exceeds the temperature-gradient scale size, so that thermal conduction becomes inherently nonlocal. Further, turbulent angular scattering, which is detectable in nonthermal widths of atomic emission lines, can also act to increase the collision frequency and thus suppress the heat flux. Recent work by Emslie & Bian extended Spitzer's theory of thermal conduction to account for both nonlocality and turbulent suppression. We have implemented their theoretical expression for the heat flux (which is a convolution of the Spitzer flux with a kernel function) into the RADYN flare-modeling code and performed a parameter study to understand how the resulting changes in thermal conduction affect the flare dynamics and hence the radiation produced. We find that models with reduced heat fluxes predict slower bulk flows, less intense line emission, and longer cooling times. By comparing the features of atomic emission lines predicted by the models with Doppler velocities and nonthermal line widths deduced from a particular flare observation, we find that models with suppression factors between 0.3 and 0.5 relative to the Spitzer value best reproduce the observed Doppler velocities across emission lines forming over a wide range of temperatures. Interestingly, the model that best matches the observed nonthermal line widths has a kappa-type velocity distribution function.

Keywords: solar flares; solar chromosphere; solar corona; radiative transfer simulations; solar ultraviolet emission; hydrodynamical simulations
The Jet and Resolved Features of the Central Supermassive Black Hole of M87 Observed with the Event Horizon Telescope (EHT)

We report the result of our independent image reconstruction of the M87 from the public data of the Event Horizon Telescope Collaborators (EHTC). Our result is different from the image published by the EHTC. Our analysis shows that (a) the structure at 230 GHz is consistent with those of lower-frequency very long baseline interferometry observations, (b) the jet structure is evident at 230 GHz extending from the core to a few milliarcsecond, although the intensity rapidly decreases along the axis, and (c) the "unresolved core" is resolved into three bright features presumably showing an initial jet with a wide opening angle of ~70°. The ring-like structures of the EHTC can be created not only from the public data but also from the simulated data of a point image. Also, the rings are very sensitive to the field-of-view (FOV) size. The u-v coverage of the Event Horizon Telescope (EHT) lacks ~ 40 μas fringe spacings. Combining with a very narrow FOV, it created the ~40 μas ring structure. We conclude that the absence of the jet and the presence of the ring in the EHTC result are both artifacts owing to the narrow FOV setting and the u-v data sampling bias effect of the EHT array. Because the EHTC's simulations only take into account the reproduction of the input image models, and not those of the input noise models, their optimal parameters can enhance the effects of sampling bias and produce artifacts such as the ~40 μas ring structure, rather than reproducing the correct image.

Keywords: supermassive black holes; very long baseline interferometry
Experimental Investigation of the Acetylene-Benzene Cocrystal on Titan

Acetylene and benzene are two common molecules formed in Titan's atmosphere, and are likely components of the lake evaporites. It is known that these two molecules can form a cocrystal, a molecule with a structure that is unique from that of the component molecules. Thus, we sought to study this cocrystal using an experimental setup that simulates Titan surface conditions (90 K, 1.5 bar). Using Fourier transform infrared (FTIR) spectroscopy, we characterize new spectral absorptions, band shifts, and morphological sample changes associated with this cocrystal from 1 to 2.6 μm, which overlaps with Cassini VIMS wavelength range (0.35-5.1 μm). This is the first study of the resulting acetylene-benzene cocrystal under Titan-relevant temperature and pressure. The cocrystal forms at 135 K and is stable down to 90 K. Our findings can be applied to the cocondensation process in Titan's atmosphere, as well as the ongoing effort to better characterize the composition and spectral properties of Titan's lake evaporites. These results can also provide a stepping stone to future surface missions such as Dragonfly, which will closely examine relevant surface materials on Titan.

Keywords: molecular spectroscopy; experimental techniques; surface ices
The Influence of Late-stage Nuclear Burning on Red Supergiant Supernova Light Curves

Many Type II supernovae (SNe) show hot early (∼30 days) emission, and a diversity in their light curves extending from the Type IIP to the Type IIL, which can be explained by interaction with dense and confined circumstellar material (CSM). We perform hydrodynamical simulations of red supergiants to model the ejection of CSM caused by wave heating during late-stage nuclear burning. Even a small amount of deposited energy (1046-1047 erg), which is roughly that expected due to waves excited by convection in the core, is sufficient to change the shapes of SN light curves and bring them into better agreement with observations. As a test case, we consider the specific example of supernova (SN) 2017eaw, which shows that a nuclear burning episode is able to explain the light curve if it occurs ∼150-450 days prior to core collapse. Due to the long timescale that it takes for the low-energy shock to traverse the star, this would manifest as a pre-SN outburst ∼50-350 days prior to the full-fledged SN. Applying work like this to other SNe will provide a direct connection between the SN and pre-SN outburst properties, which can be tested by future wide field surveys. In addition, we show that our models can qualitatively explain the short-lived "flash-ionization" lines seen in the early spectra of many Type II SNe.

Keywords: hydrodynamics; supernovae; type ii supernovae; core-collapse supernovae; radiative transfer
On the Evolutionary History of a Simulated Disk Galaxy as Seen by Phylogenetic Trees

Phylogenetic methods have long been used in biology and more recently have been extended to other fields—for example, linguistics and technology—to study evolutionary histories. Galaxies also have an evolutionary history and fall within this broad phylogenetic framework. Under the hypothesis that chemical abundances can be used as a proxy for the interstellar medium's DNA, phylogenetic methods allow us to reconstruct hierarchical similarities and differences among stars—essentially, a tree of evolutionary relationships and thus history. In this work, we apply phylogenetic methods to a simulated disk galaxy obtained with a chemodynamical code to test the approach. We found that at least 100 stellar particles are required to reliably portray the evolutionary history of a selected stellar population in this simulation, and that the overall evolutionary history is reliably preserved when the typical uncertainties in the chemical abundances are smaller than 0.08 dex. The results show that the shapes of the trees are strongly affected by the age–metallicity relation, as well as the star formation history of the galaxy. We found that regions with low star formation rates produce shorter trees than regions with high star formation rates. Our analysis demonstrates that phylogenetic methods can shed light on the process of galaxy evolution.

Keywords: galaxy abundances; galaxy chemical evolution; galaxy stellar content; interdisciplinary astronomy
Spatially Resolved Properties of Galaxies at 5 < z < 9 in the SMACS 0723 JWST ERO Field

We present the first spatially resolved measurements of galaxy properties in the JWST ERO SMACS 0723 field. We perform a comprehensive analysis of five 5 < z < 9 galaxies with spectroscopic redshifts from NIRSpec observations. We perform spatially resolved spectral energy distribution fitting with BAGPIPES, using six NIRCam imaging bands spanning the wavelength range 0.8-5 μm. This approach allows us to study the internal structure and assembly of the first generations of galaxies. We find clear gradients both in the empirical color maps and in most of the estimated physical parameters. We find regions of considerably different specific star formation rates across each galaxy, which points to very bursty star formation happening on small scales, not galaxy-wide. The integrated light is dominated by these bursty regions, which exhibit strong line emission, with the equivalent width of [O III]+Hβ reaching up to ~3000-4000 Å rest frame. Studying these galaxies in an integrated approach yields extremely young inferred ages of the stellar population (<10 Myr), which outshine older stellar populations that are only distinguishable in the spatially resolved maps. This leads to inferring ~0.5-1 dex lower stellar masses by using single-aperture photometry, when compared to resolved analyses. Such systematics would have strong implications in the shape and evolution of the stellar mass function at these early times, particularly while samples are limited to small numbers of the brightest candidates. Furthermore, the evolved stellar populations revealed in this study imply an extended process of early galaxy formation that could otherwise be hidden behind the light of the most recently formed stars.

Keywords: extragalactic astronomy; high-redshift galaxies; star forming regions
EMPRESS. III. Morphology, Stellar Population, and Dynamics of Extremely Metal-poor Galaxies (EMPGs): Are EMPGs Local Analogs of High-z Young Galaxies?

We present the morphology and stellar population of 27 extremely metal-poor galaxies (EMPGs) at z ~ 0 with metallicities of 0.01-0.1 Z⊙. We conduct multicomponent surface brightness (SB) profile fitting for the deep Subaru/Hyper Suprime-Cam i-band images of the EMPGs with the GALFIT software, carefully removing the SB contributions of tails. We find that the EMPGs with a median stellar mass of $\mathrm{log}({M}_{* }/{M}_{\odot })=6.0$ have a median Sérsic index of n = 1.1 and a median effective radius of re = 200 pc, suggesting that typical EMPGs have a very compact disk. We compare the EMPGs with z ~ 6 galaxies and local galaxies on the size-mass (re-M*) diagram, and identify that the majority of the EMPGs have an re-M* relation similar to z ~ 0 star-forming galaxies rather than z ~ 6 galaxies. Not every EMPG is a local analog of high-z young galaxies in the re-M* relation. A spectrum of one pair of EMPG and tail, so far available, indicates that the tail is dynamically related to the EMPG with a median velocity difference of ΔV = 101 ± 32 km s-1. This moderately large ΔV cannot be explained by the dynamics of the tail, but likely by the infall on the tail. For the first time, we may identify the metal-poor star-forming system just now infalling into the tail. * Released on.

Keywords: galaxy formation; galaxy structure; star formation; dwarf galaxies; galaxy kinematics
The Separation Distribution of Ultrawide Binaries across Galactic Populations

We present an extensive and pure sample of ultrawide binary stars with separations of 0.01 ≲ s/pc ≲ 1 in the solar neighborhood. Using data from Gaia DR2, we define kinematic subpopulations via the systems’ tangential velocities, I.e., disk-like (V ⊥,tot ≤ 40 km s-1), intermediate (V ⊥,tot = 40-85 km s-1), and halo-like (V ⊥,tot ≥ 85 km s-1) binaries, presuming that these velocity cuts represent a rough ordering in the binaries’ age and metallicity. Through stringent cuts on astrometric precision, we can obtain pure binary samples at such wide separations with thousands of binaries in each sample. Fitting a smoothly broken power law for the separation distribution, we find that its slope at s = 102.5-4 au is the same for all subpopulations, p(s) ∝ s γ with γ ≈ -1.54. However, the logarithmic slope of p(s) steepens at s ≳ 104 au. We find some evidences that the degree of steepening increases with the binaries’ age, with a slope change of only Δγ ≈ 0.5 for disk-like stars, but Δγ ≳ 1 for halo-like stars. This trend is contrary to what might be expected if steepening at wide separations were due to gravitational perturbations by molecular clouds or stars, which would preferentially disrupt disk binaries. If we were to interpret steepening at s ≳ 104 au as a consequence of disruption by MAssive Compact Halo Objects (MACHOs), we would have to invoke a MACHO population inconsistent with other constraints. As a more plausible alternative, we propose a simple model to predict the separation distribution of wide binaries formed in dissolving star clusters. This model generically predicts γ ≃ -1.5 as observed, with steepening at larger separations due to the finite size of binaries’ birth clusters.

Keywords: binary stars; visual binary stars; astrometric binary stars; galaxy stellar content; galaxy stellar disks; galaxy stellar halos; star formation; astrostatistics
Outbursting Young Stellar Object PGIR 20dci in the Perseus Arm

We report the discovery of a likely outbursting Class I young stellar object, associated with the star-forming region NGC 281-W (distance ∼2.8 kpc). The source is currently seen only at infrared wavelengths, appearing in both the Palomar Gattini InfraRed (1.2 μm) and the Near-Earth Object Wide-field Infrared Survey Explorer (3.4 and 4.6 μm) photometric time-domain surveys. Recent near-infrared imaging reveals a new, extended scattered light nebula. Recent near-infrared spectroscopy confirms the similarity of PGIR 20dci to FU Ori-type sources, based on strong molecular absorption in CO, H2O, and OH; weak absorption in several atomic lines; and a warm wind/outflow as indicated by a P Cygni profile in the He I λ10830 line. This is a rare case of an FU Ori star with a well-measured long-term photometric rise before a sharper outburst, and the second instance of an FU Ori star with a documented two-step brightening in the mid-infrared.

Keywords: young stellar objects; circumstellar disks; stellar accretion disks; pre-main sequence stars