adsabs/SciX_UAT_keywords huggingface dataset:
Barred Galaxies in the Illustris-1 and TNG100 Simulations: A Comparison Study

We carry out a comparison study on the bar structure in the Illustris-1 and TNG100 simulations. At z = 0, 8.9% of 1232 disk galaxies with stellar masses $\gt {10}^{10.5}{M}_{\odot }$ in Illustris-1 are barred, while the numbers are 55% of 1269 in TNG100. The bar fraction as a function of stellar mass in TNG100 agrees well with the survey ${S}^{4}G$ . The median redshifts of bar formation are ∼0.4-0.5 and ∼0.25 in TNG100 and Illustris-1, respectively. Bar fraction generally increases with stellar mass and decreases with gas fraction in both simulations. For galaxies with bars at z = 0, their bar formation time is generally anti-correlated with their gas fraction at high redshift. When the bars were formed, the disk gas fractions were mostly lower than 0.4. The much higher bar fraction in TNG100 probably benefits from the much lower gas fractions in massive disk galaxies since z ∼ 3, which may result from the combination of more effective stellar and AGN feedback. The latter may be the primary factor at z < 2. Meanwhile, in both simulations, barred galaxies have higher star formation rates before bar formation and have stronger AGN feedback, at all times, than unbarred galaxies. The properties of dark matter halos hosting massive disk galaxies are similar between the two simulations and should have a minor effect on the frequencies of different bars. For individual galaxies under similar halo environments across the two simulations, different baryonic physics can lead to striking discrepancies in morphology. The morphologies of individual galaxies are subject to the combined effects of environment and internal baryonic physics and are often not predictable.

Keywords: galaxy structure; galaxy evolution; galaxy dark matter halos; hydrodynamical simulations; barred spiral galaxies
An Elusive Population of Massive Disk Galaxies Hosting Double-lobed Radio-loud Active Galactic Nuclei

It is commonly accepted that radio-loud active galactic nuclei are hosted exclusively by giant elliptical galaxies. We analyze high-resolution optical Hubble Space Telescope images of a sample of radio galaxies with extended double-lobed structures associated with disk-like optical counterparts. After systematically evaluating the probability of chance alignment between the radio lobes and the optical counterparts, we obtain a sample of 18 objects likely to have genuine associations. The host galaxies have unambiguous late-type morphologies, including spiral arms, large-scale dust lanes among the edge-on systems, and exceptionally weak bulges, as judged by the low global concentrations, small global Sérsic indices, and low bulge-to-total light ratios (median B/T = 0.13). With a median Sérsic index of 1.4 and low effective surface brightnesses, the bulges are consistent with being pseudobulges. The majority of the hosts have unusually large stellar masses (median M * = 1.3 × 1011 M ⊙) and red optical colors (median g - r = 0.69 mag), consistent with massive, quiescent galaxies on the red sequence. We suggest that the black hole mass (stellar mass) plays a fundamental role in launching large-scale radio jets, and that the rarity of extended radio lobes in late-type galaxies is the consequence of the steep stellar mass function at the high-mass end. The disk radio galaxies have mostly Fanaroff-Riley type II morphologies yet lower radio power than sources of a similar type traditionally hosted by ellipticals. The radio jets show no preferential alignment with the minor axis of the galactic bulge or disk, apart from a possible mild tendency for alignment among the most disk-dominated systems.

Keywords: radio jets; radio loud quasars; agn host galaxies; active galactic nuclei; galaxy nuclei; radio active galactic nuclei; radio galaxies; galaxy masses; active galaxies; quasars
An Exact, Generalized Laplace Resonance in the HR 8799 Planetary System

A system of four super-Jupiter planets around HR 8799 is the first multiplanet configuration discovered via the direct imaging technique. Despite over a decade of research, the system's architecture is still not fully resolved. The main difficulty comes from a still narrow observing window of ∼20 yr that covers small arcs of orbits with periods from roughly 50 to 500 yr. Soon after the discovery, it became clear that unconstrained best-fitting astrometric configurations self-disrupt rapidly due to strong mutual gravitational interactions between the companions of ≃10 Jupiter mass. Recently, we showed that the HR 8799 system may be long-term stable when locked in a generalized Laplace 8:4:2:1 mean-motion resonance (MMR) chain, and we constrained its orbits through the planetary migration. Here we qualitatively improve this approach by considering the MMR in terms of an exactly periodic configuration. This assumption enables us to construct for the first time the self-consistent N-body model of the long-term stable orbital architecture using only available astrometric positions of the planets relative to the star. We independently determine the planetary masses, which are consistent with thermodynamic evolution, and the parallax overlapping to 1σ with the most recent Gaia DR2 value. We also determine the global structure of the inner and outer debris disks in the [8, 600] au range, consistent with the updated orbital solution.

Keywords: exoplanet dynamics; exoplanet systems; exoplanet detection methods
Response of Global Ionospheric Currents to Solar Flares with Extreme Ultraviolet Late Phases

It is known that solar flares can affect the current system of the middle- and low-latitude ionosphere. Most earlier studies have focused on such effects during their impulsive phases. Recent studies have reported flares with a significant extreme ultraviolet (EUV) late phase, the effects of which on ionospheric currents have not yet been investigated. Here, we examine the solar quiet (Sq) currents and equatorial electrojets during two X-class flares with EUV late phases using data from more than 200 ground magnetometers. Our results indicate that the ionospheric currents could be significantly enhanced during the impulsive phase, while the effects of the EUV late phase may increase the global ionospheric currents, but are often weak and thus could be obscured by a change in solar wind conditions. In the X1.8 flare event on 2012 October 23, besides the solar flare effects, the currents were modulated by solar wind pressure. In the X1.3 flare event on 2014 April 25, the solar wind pressure was weak and stable, and the Sq currents were enhanced compared to nonflare conditions. We also found that even weak changes in the solar wind dynamic pressure, with magnitudes as low as ∼2 nPa, which are often ignored, may have an appreciable impact on the global ionospheric current system.

Keywords: solar flares; earth ionosphere; solar extreme ultraviolet emission
Updated Reference Wavelengths for Si VII and Mg VII Lines in the 272-281 Å Range

New reference wavelengths for atomic transitions of Mg VII and Si VII in the 272-281 Å wavelength range are derived using measurements from the Extreme-ultraviolet Imaging Spectrometer (EIS) on board the Hinode spacecraft. Mg VII and Si VII are important ions for measuring plasma properties in the solar transition region at around 0.6 MK. The six Si VII wavelengths are 13-21 mÅ and 7-11 mÅ longer than the values in the NIST Atomic Spectra Database (ASD) and the compilations of B. Edlén, respectively. The four Mg VII wavelengths are shorter than the values in the ASD by 8-12 mÅ but show reasonable agreement with the Edlén values. The new wavelengths will lead to more accurate Doppler shift measurements from the EIS instrument and will be valuable for spectral disambiguation modeling for the upcoming Multi-Slit Solar Explorer mission.

Keywords: ultraviolet spectroscopy; solar atmosphere; solar transition region; atomic data
TESS Discovery of a Super-Earth and Three Sub-Neptunes Hosted by the Bright, Sun-like Star HD 108236

We report the discovery and validation of four extrasolar planets hosted by the nearby, bright, Sun-like (G3V) star HD 108236 using data from the Transiting Exoplanet Survey Satellite (TESS). We present transit photometry, reconnaissance, and precise Doppler spectroscopy, as well as high-resolution imaging, to validate the planetary nature of the objects transiting HD 108236, also known as the TESS Object of Interest (TOI) 1233. The innermost planet is a possibly rocky super-Earth with a period of ${3.79523}_{-0.00044}^{+0.00047}$ days and has a radius of 1.586 ± 0.098 R⊕. The outer planets are sub-Neptunes, with potential gaseous envelopes, having radii of ${2.068}_{-0.091}^{+0.10}$ R⊕, 2.72 ± 0.11 R⊕, and ${3.12}_{-0.12}^{+0.13}$ R⊕ and periods of ${6.20370}_{-0.00052}^{+0.00064}$ days, ${14.17555}_{-0.0011}^{+0.00099}$ days, and ${19.5917}_{-0.0020}^{+0.0022}$ days, respectively. With V and Ks magnitudes of 9.2 and 7.6, respectively, the bright host star makes the transiting planets favorable targets for mass measurements and, potentially, for atmospheric characterization via transmission spectroscopy. HD 108236 is the brightest Sun-like star in the visual (V) band known to host four or more transiting exoplanets. The discovered planets span a broad range of planetary radii and equilibrium temperatures and share a common history of insolation from a Sun-like star (R⋆ = 0.888 ± 0.017 R⊙, Teff = 5730 ± 50 K), making HD 108236 an exciting, opportune cosmic laboratory for testing models of planet formation and evolution.

Keywords: exoplanet astronomy; exoplanet detection methods; exoplanet atmospheres; exoplanet dynamics
The Value of Progenitor Radius Measurements for Explosion Modeling of Type II-Plateau Supernovae

Using Modules for Experiments in Stellar Astrophysics (MESA)+STELLA, we show that very different physical models can adequately reproduce a specific observed Type II-Plateau supernova (SN). We consider SN2004A, SN2004et, SN2009ib, SN2017eaw, and SN2017gmr, nickel-rich ( ${M}_{\mathrm{Ni}}\gt 0.03{M}_{\odot }$ ) events with bolometric lightcurves and a well-sampled decline from the plateau. These events also have constraints on the progenitor radius, via a progenitor image, or, in the case of SN2017gmr, a radius from fitting shock-cooling models. In general, many explosions spanning the parameter space of progenitors can yield excellent lightcurve and Fe-line velocity agreement, demonstrating the success of scaling laws in motivating models that match plateau properties for a given radius and highlighting the degeneracy between plateau luminosity and velocity in models and observed events, which can span over 50% in ejecta mass, radius, and explosion energy. This can help explain disagreements in explosion properties reported for the same event using different model calculations. Our calculations yield explosion properties when combined with pre-explosion progenitor radius measurements or a robust understanding of the outermost $\lt 0.1\,{M}_{\odot }$ of material that quantifies the progenitor radius from SN observations a few days after explosion.

Keywords: massive stars; type ii supernovae; supernovae; hydrodynamical simulations; radiative transfer simulations; stellar evolutionary models; light curves
BASS. XXIII. A New Mid-infrared Diagnostic for Absorption in Active Galactic Nuclei

In this study, we use the Swift/BAT AGN sample, which has received extensive multiwavelength follow-up analysis as a result of the BAT AGN Spectroscopic Survey, to develop a diagnostic for nuclear obscuration by examining the relationship between the line-of-sight column densities (N H), the 2–10 keV to 12 μm luminosity ratio, and WISE mid-infrared colors. We demonstrate that heavily obscured AGNs tend to exhibit both preferentially "redder" mid-infrared colors and lower values of L X,Obs./L 12 μm than less obscured AGNs, and we derive expressions relating N H to the L X,Obs./L 12 μm and L 22 μm/L 4.6 μm luminosity ratios, as well as develop diagnostic criteria using these ratios. Our diagnostic regions yield samples that are ≳80% complete and ≳60% pure for AGNs with log(N H/cm‑2) ≥ 24, as well as ≳85% pure for AGNs with . We find that these diagnostics cannot be used to differentiate between optically star-forming galaxies and active galaxies. Further, mid-IR contributions from host galaxies that dominate the observed 12 μm emission can lead to larger apparent X-ray deficits and redder mid-IR colors than the AGNs would intrinsically exhibit, though this effect helps to better separate less and more obscured AGNs. Finally, we test our diagnostics on two catalogs of AGNs and infrared galaxies, including the XMM-Newton XXL-N field, and we identify several known Compton-thick AGNs, as well as a handful of candidate heavily obscured AGNs based upon our proposed obscuration diagnostics.

Keywords: supermassive black holes; active galactic nuclei; black hole physics; x-ray active galactic nuclei; agn host galaxies
A Curious Case of Circular Polarization in the 25 GHz Methanol Maser Line toward OMC-1

We report the detection of a circular polarization signature in the Stokes V profile of a 25 GHz Class I CH3OH maser toward the high-mass star-forming region OMC-1. Such a feature usually constitutes a detection of the Zeeman effect. If due to a magnetic field in OMC-1, this would represent the first detection and discovery of the Zeeman effect in the 25 GHz Class I CH3OH maser. The feature in Stokes V is detected in two observations with different angular resolutions taken eight years apart with the Very Large Array; for our 2009 D-configuration observations, the fitted value for z ${B}_{\mathrm{los}}$ is 152 ± 12 Hz, where z is the Zeeman splitting factor and ${B}_{\mathrm{los}}$ is the line-of-sight magnetic field. For our 2017 C-configuration observations, the fitted value for z ${B}_{\mathrm{los}}$ = 149 ± 19 Hz, likely for the same maser spot. These correspond to ${B}_{\mathrm{los}}$ in the range 171-214 mG, depending on which hyperfine transition is responsible for the maser line. While these ${B}_{\mathrm{los}}$ values are high, they are not implausible. If the magnetic field increases in proportion to the molecular hydrogen density in shocked regions, then our detected fields predict values for the pre-shock magnetic field that are in agreement with observations. With ${B}_{\mathrm{los}}$ = 171-214 mG, the magnetic energy in the post-shocked regions where these 25 GHz Class I CH3OH masers occur would dominate over the kinetic energy density and be at least of the order of the pressure in the shock, implying that the magnetic field would exert significant influence over the dynamics of these regions.

Keywords: interstellar medium; astrophysical masers; interstellar magnetic fields; interstellar molecules; high resolution spectroscopy; star formation; star forming regions; polarimetry
The Role of Filamentary Structures in the Formation of Two Dense Cores, L1544 and L694-2

We present mapping results of two prestellar cores, L1544 and L694-2, embedded in filamentary clouds in C18O (3-2), 13CO (3-2), 12CO (3-2), HCO+ (4-3), and H13CO+ (4-3) lines with the James Clerk Maxwell Telescope to examine the role of the filamentary structures in the formation of dense cores in the clouds, with new distance estimates for L1544 ( ${175}_{-3}^{+4}$ pc) and L694-2 ( ${203}_{-7}^{+6}$ pc). From these observations, we found that the nonthermal velocity dispersion of two prestellar cores and their surrounding clouds is smaller than or comparable to the sound speed. This may indicate that the turbulence has already been dissipated for both filaments and cores during their formation time. We also found a λ/4 shift between the periodic oscillations in the velocity and the column density distributions, implying the possible presence of gravitational core-forming flow motion along the axis of the filament. The mass accretion rates due to these flow motions are estimated to be 2-3 M ⊙ Myr-1, being comparable to that for Serpens cloud but much smaller than those for the Hub filaments, cluster, or high-mass forming filaments by 1 or 2 orders of magnitude. From this study, we suggest that the filaments in our targets might be formed from the shock compression of colliding clouds, and then the cores are formed by gravitational fragmentation of the filaments to evolve to the prestellar stage. We conclude that the filamentary structures in the clouds play an important role in the entire process of formation of dense cores and their evolution.

Keywords: star formation; star forming regions; molecular clouds; interstellar filaments; interstellar line emission; dust continuum emission
The Chandra Cygnus OB2 Legacy Survey: Design and X-Ray Point-source Catalog

The Cygnus OB2 association is the largest concentration of young and massive stars within 2 kpc of the Sun, including an estimated ~65 O-type stars and hundreds of OB stars. The Chandra Cygnus OB2 Legacy Survey is a large imaging program undertaken with the Advanced CCD Imaging Spectrometer on board the Chandra X-ray Observatory. The survey has imaged the central 0.5 deg2 of the Cyg OB2 association with an effective exposure of ~120 ks and an outer 0.35 deg2 area with an exposure of ~60 ks. Here we describe the survey design and observations, discuss the data reduction and source detection, and present a catalog of ~8000 X-ray point sources. The survey design employs a grid of 36 heavily (~50%) overlapping pointings, a method that overcomes Chandra's low off-axis sensitivity and produces a highly uniform exposure over the inner 0.5 deg2. The full X-ray catalog is described here and is made available online.

Keywords: x-ray stars; pre-main sequence stars; massive stars
Measurement of the Angular Momenta of Pre-main-sequence Stars: Early Evolution of Slow and Fast Rotators and Empirical Constraints on Spin-down Torque Mechanisms

We use TESS full-frame imaging data to investigate the angular momentum evolution of young stars in the Orion Complex. We confirm recent findings that stars with rotation periods faster than 2 days are overwhelmingly binaries, with typical separations of tens of au; such binaries quickly clear their disks, leading to a tendency for rapid rotators to be diskless. Among (nominally single) stars with rotation periods slower than 2 days, we observe the familiar gyrochronological horseshoe-shaped relationship of rotation period versus T eff, indicating that the processes that govern the universal evolution of stellar rotation on gigayear timescales are already in place within the first few megayears. Using spectroscopic $v\sin i$ , we determine the distribution of $\sin i$ , revealing that the youngest stars are biased toward more pole-on orientations, which may be responsible for the systematics between stellar mass and age observed in star-forming regions. We are also able for the first time to make empirical, quantitative measurements of angular momenta and their time derivatives as functions of stellar mass and age, finding these relationships to be much simpler and monotonic as compared to the complex relationships involving rotation period alone; evidently, the relationship between rotation period and T eff is largely a reflection of mass-dependent stellar structure and not of angular momentum per se. Our measurements show that the stars experience spin-down torques in the range of ~1037 erg at ~1 Myr to ~1035 erg at ~10 Myr, which provide a crucial empirical touchstone for theoretical mechanisms of angular momentum loss in young stars.

Keywords: stellar rotation; young stellar objects; early stellar evolution; inclination; binary stars
Interaction between a Coronal Mass Ejection and Comet 67P/Churyumov–Gerasimenko

The interaction between a coronal mass ejection (CME) and a comet has been observed several times by in situ observations from the Rosetta Plasma Consortium, which is designed to investigate the cometary magnetosphere of comet 67P/Churyumov–Gerasimenko (CG). Goetz et al. reported a magnetic field of up to 300 nT measured in the inner coma, which is among the largest interplanetary magnetic fields observed in the solar system. They suggested the large magnetic field observations in the inner coma come from magnetic field pileup regions, which are generated by the interaction between a CME and/or corotating interaction region and the cometary magnetosphere. However, the detailed interaction between a CME and the cometary magnetosphere of comet CG in the inner coma has not been investigated by numerical simulations yet. In this paper, we will use a numerical model to simulate the interaction between comet CG and a Halloween class CME and investigate its magnetospheric response to the CME. We find that the plasma structures change significantly during the CME event, and the maximum value of the magnetic field strength is more than 500 nT close to the nucleus. Virtual satellites at similar distances as Rosetta show that the magnetic field strength can be as large as 250 nT, which is slightly less than what Goetz et al. reported.

Keywords: magnetohydrodynamics; solar coronal mass ejections; comets
The Metallicity and Distance of Leo A from Blue Supergiants

We have obtained high-quality spectra of blue supergiant candidates in the dwarf irregular galaxy Leo A with the Low Resolution Imaging Spectrometer at the Keck I telescope. From the quantitative analysis of seven B8-A0 stars, we derive a mean metallicity [Z] = -1.35 ± 0.08, in excellent agreement with the gas-phase chemical abundance. From the stellar parameters and the flux-weighted gravity-luminosity relation (FGLR), we derive a spectroscopic distance modulus m - M = 24.77 ± 0.11 mag, significantly larger (~0.4 mag) than the value indicated by RR Lyrae and other stellar indicators. We explain the bulk of this discrepancy with blue loop stellar evolution at very low metallicity and show that the combination of metallicity effects and blue loop evolution amounts, in the case of Leo A, to an ~0.35 mag offset of the FGLR to fainter bolometric luminosities. We identify one outlier of low bolometric magnitude as a post-AGB star. Its metallicity is consistent with that of the young population, confirming the slow chemical enrichment of Leo A.

Keywords: galaxy abundances; galaxy stellar content; stellar abundances
On the Lifetime of Molecular Clouds with the "Tuning-fork" Analysis

The "tuning-fork" (TF) analysis of CO and Hα emission has been used to estimate the lifetimes of molecular clouds in nearby galaxies. With simple model calculations, we show that this analysis does not necessarily estimate cloud lifetimes, but instead captures a duration of the cloud evolutionary cycle, from dormant to star-forming, and then back to a dormant phase. We adopt a hypothetical setup in which molecular clouds (e.g., traced in CO) live forever and form stars (e.g., H II regions) at some frequency, which then drift away from the clouds. The TF analysis still returns a timescale for the immortal clouds. This model requires drifting motion to separate the newborn stars from the clouds, and we discuss its origin. We also discuss the physical origin of the characteristic spatial separation term in the TF analysis and a bias due to systematic error in the determination of the reference timescale.

Keywords: star formation; molecular clouds; galaxy evolution; interstellar medium