adsabs/SciX_UAT_keywords huggingface dataset:
X-Ray Observations of a [C II]-bright, z = 6.59 Quasar/Companion System

We present deep Chandra observations of PSO J231.6576-20.8335, a quasar at redshift z = 6.59 with a nearby (∼8 proper kpc) companion galaxy. The Atacama Large Millimeter/submillimeter Array observed both the quasar and companion to be bright in [C II], and the system has significant extended Lyα emission around the quasar, suggesting that a galaxy merger is ongoing. Unlike previous studies of two similar systems, and despite observing the system with Chandra for 140 ks, we do not detect the companion in X-rays. The quasar itself is detected, but only ${13.3}_{-3.7}^{+4.8}$ net counts are observed. From a basic spectral analysis, the X-ray spectrum of the quasar is soft (hardness ratio of ${ \mathcal H }{ \mathcal R }=-{0.60}_{-0.27}^{+0.17}$ , power-law index of ${\rm{\Gamma }}={2.6}_{-0.9}^{+1.0}$ ), which results in a rest-frame X-ray luminosity comparable to other bright quasars ( ${L}_{2\mbox{--}10}={1.09}_{-0.70}^{+2.20}\times {10}^{45}\ \mathrm{erg}\ {{\rm{s}}}^{-1}$ ) despite the faint observed X-ray flux. We highlight two possible interpretations of this result: the quasar has a steep value of Γ—potentially related to observed ongoing Eddington accretion—thereby pushing much of the emission out of our observed band, or the quasar has a more normal spectrum (Γ ∼ 2) but is therefore less X-ray luminous ( ${L}_{2\mbox{--}10}\sim 0.6\times {10}^{45}\ \mathrm{erg}\ {{\rm{s}}}^{-1}$ ).

Keywords: x-ray quasars; x-ray astronomy; galaxy mergers; quasars; quasar-galaxy pairs
X-Ray Jets in the High-redshift Quasars J1405+0415 and J1610+1811

We investigate Chandra X-ray observations of the radio-loud quasars J1405+0415 and J1610+1811 at redshifts z = 3.215 and z = 3.122, respectively, for evidence of extended X-ray emission. Observations totalling 95 ks per target are combined, and X-ray jets that are spatially coincident with known radio features are detected at a greater than 4σ significance. Hardness ratios and emission spectra are determined for all X-ray features, and X-ray fluxes and luminosities are measured. Jet-to-core X-ray flux ratios are estimated for each system, and the ratios are consistent with those observed for nearby and more distant jet systems, although the spread in the parameter is large. These results suggest that to first order the X-ray jet emission mechanisms are redshift invariant. In addition to the extended emission analysis, incorporating also archival data from Swift, we examined the properties of a decline in the Chandra flux from the active galactic nucleus (AGN) of J1610+1811 observed between 2018 and 2021. We conclude that the variability is most likely due to a flaring event that occurred between the years 2017 and 2018 and originated from either the AGN or the inner jet region.

Keywords: high-redshift galaxies; jets; x-ray active galactic nuclei
Searching for Compact Objects in Binaries with Gaia DR3

We search for compact objects in binaries based on Gaia DR3. A sample of 10 targets is derived under the following conditions: the radial velocity variable, low temperature (T eff < 6000 K), high mass function (f(M 2) > 1M ⊙), and ellipsoidal-like light curves. Two targets have LAMOST spectroscopic observations, one of which is a double-lined spectroscopic binary. The observational data of seven targets are not self-consistent, since their photometric periods are even shorter than the theoretical minimum orbital periods calculated by the stellar parameters from Gaia DR3. After excluding these seven inconsistent targets and another target contaminated by a near-bright star, the remaining two targets may contain compact objects worth follow-up observations. This work may serve as an example to demonstrate the feasibility of searching for compact objects in the massive Gaia data.

Keywords: close binary stars; compact binary stars; light curves; radial velocity; spectroscopic binary stars
Light Bridge and Magnetic Field in a Solar Active Region

Observational data from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory and the multiwavelength simultaneous imaging system attached to the New Vacuum Solar Telescope located at Fuxian Lake, China are employed for the study of light bridges and magnetic fields in the active region NOAA 12529. Coronal fields in this active region are computed with a boundary integration model and the field line connectivity in the dominant spot is investigated with the squashing factor Q. Quasi separatrix layer intersections in the CCD coordinate plane are determined according to values of Q. It is found that weak field lanes (WFLs) appear in the umbra and penumbra; open and closed flux systems are separated by QSLs in the dominant spot; and WFLs and QSLs look quite different from each other in the dominant spot but partially overlap in the umbra. Our study demonstrates that WFLs cannot be attributed to topological evolution of magnetic fields and might be regarded as rifts among splitting flux systems.

Keywords: solar active region magnetic fields; sunspots
A Model of Double Coronal Hard X-Ray Sources in Solar Flares

A number of double coronal X-ray sources have been observed during solar flares by RHESSI, where the two sources reside at different sides of the inferred reconnection site. However, where and how these X-ray-emitting electrons are accelerated remains unclear. Here we present the first model of the double coronal hard X-ray (HXR) sources, where electrons are accelerated by a pair of termination shocks driven by bidirectional fast reconnection outflows. We model the acceleration and transport of electrons in the flare region by numerically solving the Parker transport equation using velocity and magnetic fields from the macroscopic magnetohydrodynamic simulation of a flux rope eruption. We show that electrons can be efficiently accelerated by the termination shocks and high-energy electrons mainly concentrate around the two shocks. The synthetic HXR emission images display two distinct sources extending to >100 keV below and above the reconnection region, with the upper source much fainter than the lower one. The HXR energy spectra of the two coronal sources show similar spectral slopes, consistent with the observations. Our simulation results suggest that the flare termination shock can be a promising particle acceleration mechanism in explaining the double-source nonthermal emissions in solar flares.

Keywords: solar flares; non-thermal radiation sources; solar magnetic reconnection; solar particle emission; shocks; solar x-ray emission
The Breakdown Scale of H I Bias Linearity

The 21 cm intensity mapping experiments promise to obtain the large-scale distribution of H I gas at the post-reionization epoch. In order to reveal the underlying matter density fluctuations from the H I mapping, it is important to understand how H I gas traces the matter density distribution. Both nonlinear halo clustering and nonlinear effects modulating H I gas in halos may determine the scale below which the H I bias deviates from linearity. We employ three approaches to generate the mock H I density from a large-scale N-body simulation at low redshifts, and demonstrate that the assumption of H I linearity is valid at the scale corresponding to the first peak of baryon acoustic oscillations, but breaks down at k ≳ 0.1 h Mpc-1. The nonlinear effects of halo clustering and H I content modulation counteract each other at small scales, and their competition results in a model-dependent "sweet-spot" redshift near z = 1, where the H I bias is scale-independent down to small scales. We also find that the linear H I bias scales approximately linearly with redshift for z ≤ 3.

Keywords: h i line emission; line intensities; galaxy dark matter halos; large-scale structure of the universe
Nucleosynthetic Analysis of Three-dimensional Core-collapse Supernova Simulations

We study in detail the ejecta conditions and theoretical nucleosynthetic results for 18 three-dimensional core-collapse supernova (CCSN) simulations done by FORNAX. Most of the simulations are carried out to at least 3 s after bounce, which allows us to follow their longer-term behaviors. We find that multidimensional effects introduce many complexities into the ejecta conditions. We see a stochastic electron fraction evolution, complex peak temperature distributions and histories, and long-tail distributions of the time spent within nucleosynthetic temperature ranges. These all lead to substantial variation in CCSN nucleosynthetic yields and differences from 1D results. We discuss the production of lighter α-nuclei, radioactive isotopes, heavier elements, and a few isotopes of special interest. Comparing pre-CCSN and CCSN contributions, we find that a significant fraction of elements between roughly Si and Ge are generally produced in CCSNe. We find that 44Ti exhibits an extended production timescale as compared to 56Ni, which may explain its different distribution and higher than previously predicted abundances in supernova remnants such as Cas A and SN1987A. We also discuss the morphology of the ejected elements. This study highlights the high-level diversity of ejecta conditions and nucleosynthetic results in 3D CCSN simulations and emphasizes the need for additional long-term (∼10 s) 3D simulations to properly address such complexities.

Keywords: core-collapse supernovae; nucleosynthesis
Period-Luminosity Relations for Galactic Classical Cepheids in the Sloan Bands

We present the first period-luminosity (PL) and period-Wesenheit (PW) relations in the Sloan-Pan-STARRS g P1 r P1 i P1 bands for classical fundamental-mode Cepheids in the Milky Way. We used a relatively modest number of 76 stars for the PL and 84-85 stars for the PW relations calibration. The data for the project were collected with the network of 40 cm telescopes of the Las Cumbres Observatory, and Gaia Data Release 3 parallaxes were used for the calculations. These gri-band PL and PW relations calibrations will be a useful tool for distance determinations in the era of large sky surveys using the Sloan photometric system, especially with the near-future start of the Large Synoptic Survey of Space and Time. * Based on data from the Las Cumbres Observatory.

Keywords: cepheid variable stars; pulsating variable stars; milky way galaxy; distance indicators; sloan photometry
Photometric Survey of Neptune's Trojan Asteroids. I. The Color Distribution

In 2018, Jewitt identified the "The Trojan Color Conundrum," namely that Neptune's Trojan asteroids (NTs) had no ultrared members, unlike the the nearby Kuiper Belt. Since then, numerous ultrared NTs have been discovered, seemingly resolving this conundrum. However, it is still unclear whether or not the Kuiper Belt has a color distribution consistent with the NT population, as would be expected if it were the source population. In this work, we present a new photometric survey of 15 out of 31 NTs. We utilized the Sloan $g^{\prime} r^{\prime} i^{\prime} z^{\prime} $ filters on the IMACS f/4 instrument, which is mounted on the 6.5 m Baade telescope. In this survey, we identify four NTs as being ultrared using a principal component analysis. This result brings the ratio of red to ultrared NTs to 7.75:1, more consistent with the corresponding trans-Neptunian object ratio of 4-11:1. We also identify three targets as being blue (nearly solar) in color. Such objects may be C-type surfaces, but we see more of these blue NTs than has been observed in the Kuiper Belt. Finally, we show that there are hints of a color-absolute magnitude (H) correlation, with larger H (smaller sized, lower albedo) tending to be more red, but more data are needed to confirm this result. The origin of such a correlation remains an open question that will be addressed by future observations of the surface composition of these targets and their rotational properties.

Keywords: trojan asteroids; neptune trojans; multi-color photometry; ccd photometry
N-body Simulations of the Ring Formation Process around the Dwarf Planet Haumea

Haumea is the only known trans-Neptunian object with a ring. The ring is in a position that causes a 3:1 spin-orbit resonance with the rotational period of Haumea, which has a triaxial shape. The non-axisymmetric gravitational field around Haumea is thought to affect the dynamics of the ring; however, the process of ring formation has not been elucidated. In this study, we analyze in some detail a potential ring formation scenario for Haumea. We first calculated the gravitational field around the triaxial ellipsoid and estimated the distance at which an object revolving around Haumea can exist stably using a simulation that incorporated the time-varying gravitational field. The results of this simulation showed that the trajectory of the object became unstable just inside its current ring position. Next, we analytically derived the Roche radius for a rigid body revolving around a triaxial ellipsoid and showed that the Roche radius could be near the current ring position. Furthermore, as a parameter study, we performed N-body simulations using the coefficient of rubble-pile restitution as a variable. Results demonstrated that, according to numerous parameters, the position of the Roche radius was near the current position of Haumea's ring. Based on these findings, we can assume that there is a high possibility that the ring formed in the region between the boundary of the unstable region of the orbit and the Roche radius. The scenario presented in this study could help explain the process by which Haumea's ring formed.

Keywords: solar system; n-body simulations; solar system formation; dwarf planets; planetary rings
MESSENGER Observations of Multiple Magnetic Energy Releases during Mercury's Substorm

Substorms are energy storage and dissipation processes that occur in planetary magnetospheres accompanied by numerous phenomena, such as magnetic dipolarizations, plasma sheet thinning and thickening, magnetic flux ropes, and plasmoid ejections. Recent MESSENGER observations have revealed substorm activity in Mercury's near magnetotail, with average durations of 2-3 minutes for both the growth and expansion phases. Herein, we report MESSENGER spacecraft observations of sporadic and short-term energy dissipation processes during the substorm expansion phase in Mercury's magnetotail. Three magnetic dipolarizations lasting for ~4 minutes were detected during the expansion phase and manifested as step-like enhancements in the northward component of the magnetic field. The magnetic field strength decreased during each dipolarization, indicating an intermittent release of magnetic energy. They arise owing to multiple magnetic pileup effects caused by planetward bursty bulk flows ejected from distant magnetotail reconnections. Additionally, in close proximity to each dipolarization, we observed the occurrence of pulse-like fluctuations in the B y component. These new MESSENGER observations suggest that during the expansion phase of Mercury's substorm, the energy dissipation can be caused by multiple local transient processes, although the duration is much shorter than that of Earth.

Keywords: magnetic fields; mercury (planet); solar magnetic reconnection; plasma physics; space plasmas; planetary magnetospheres
Ultra-short-period Planets in K2. III. Neighbors are Common with 13 New Multiplanet Systems and 10 Newly Validated Planets in Campaigns 0-8 and 10

Using the EVEREST photometry pipeline, we have identified 74 candidate ultra-short-period planets (USPs; orbital period P < 1 day) in the first half of the K2 data (Campaigns 0-8 and 10). Of these, 33 candidates have not previously been reported. A systematic search for additional transiting planets found 13 new multiplanet systems containing a USP, doubling the number known and representing a third (32%) of USPs in our sample from K2. We also identified 30 companions, which have periods from 1.4 to 31 days (median 5.5 days). A third (36 of 104) of the candidate USPs and companions have been statistically validated or confirmed in this work, 10 for the first time, including 7 USPs. Almost all candidates, and all validated planets, are small (radii Rp ≤ 3 R⊕) with a median radius of Rp = 1.1 R⊕; the validated and confirmed USP candidates have radii between 0.4 R⊕ and 2.4 R⊕ and periods from P = 0.18 to 0.96 days. The lack of candidate (a) ultra-hot-Jupiter (Rp > 10 R⊕) and (b) short-period-desert (3 ≤ Rp ≤ 10 R⊕) planets suggests that both populations are rare, although our survey may have missed some of the very deepest transits. These results also provide strong evidence that we have not reached a lower limit on the distribution of planetary radius values for planets at close proximity to a star and suggest that additional improvements in photometry techniques would yield yet more USPs. The large fraction of USPs in known multiplanet systems supports origins models that involve dynamical interactions with exterior planets coupled to tidal decay of the USP orbits.

Keywords: transit photometry; exoplanet catalogs; exoplanet formation; exoplanet evolution
Calibrating Cosmological Simulations with Implicit Likelihood Inference Using Galaxy Growth Observables

In a novel approach employing implicit likelihood inference (ILI), also known as likelihood-free inference, we calibrate the parameters of cosmological hydrodynamic simulations against observations, which has previously been unfeasible due to the high computational cost of these simulations. For computational efficiency, we train neural networks as emulators on ~1000 cosmological simulations from the CAMELS project to estimate simulated observables, taking as input the cosmological and astrophysical parameters, and use these emulators as surrogates for the cosmological simulations. Using the cosmic star formation rate density (SFRD) and, separately, the stellar mass functions (SMFs) at different redshifts, we perform ILI on selected cosmological and astrophysical parameters (Ω m , σ 8, stellar wind feedback, and kinetic black hole feedback) and obtain full six-dimensional posterior distributions. In the performance test, the ILI from the emulated SFRD (SMFs) can recover the target observables with a relative error of 0.17% (0.4%). We find that degeneracies exist between the parameters inferred from the emulated SFRD, confirmed with new full cosmological simulations. We also find that the SMFs can break the degeneracy in the SFRD, which indicates that the SMFs provide complementary constraints for the parameters. Further, we find that a parameter combination inferred from an observationally inferred SFRD reproduces the target observed SFRD very well, whereas, in the case of the SMFs, the inferred and observed SMFs show significant discrepancies that indicate potential limitations of the current galaxy formation modeling and calibration framework, and/or systematic differences and inconsistencies between observations of the SMFs.

Keywords: nonparametric inference; likelihood ratio test; magnetohydrodynamical simulations; cosmological parameters; neural networks; bayes' theorem; galaxy formation
The Statistical Polarization Properties of Coherent Curvature Radiation by Bunches: Application to Fast Radio Burst Repeaters

Fast radio bursts (FRBs) are extragalactic radio transients with a millisecond duration and an extremely high brightness temperature. Very recently, some highly circularly polarized bursts were found in a repeater, FRB 20201124A. The significant circular polarization might be produced by coherent curvature radiation by bunches with the line of sight (LOS) deviating from the bunch central trajectories. In this work, we carry out simulations to study the statistical properties of burst polarization within the framework of coherent curvature radiation by charged bunches in the neutron star magnetosphere for repeating FRBs. The flux is almost constant within the opening angle of the bunch. However, when the LOS derives from the bunch opening angle, the larger the derivation, the larger the circular polarization but the lower the flux. We investigate the statistical distribution of circular polarization and flux of radio bursts from an FRB repeater, and find that most of the bursts with high circular polarization have a relatively low flux. Besides, we find that most of the depolarization degrees of bursts have a small variation in a wide frequency band. Furthermore, we simulate the polarization angle (PA) evolution and find that most bursts show a flat PA evolution within the burst phases, and some bursts present a swing of the PA.

Keywords: radio bursts; radio transient sources; magnetars; radiative processes
Properties of Highly Rotationally Excited H2 in Photodissociation Regions

Molecular hydrogen (H2) is the dominant molecular species in the vast majority of interstellar environments and it plays a crucial role as a radiative coolant. In photodissociation regions (PDRs), it is one of the primary emitters in the near- to mid-infrared, which is due to lines originating from highly excited levels. The sparseness of H2 collisional data for rotational levels J ≥ 9, particularly for H2-H2 collisions, has limited nonlocal thermal equilibrium (NLTE) studies in ultraviolet-irradiated regions. Utilizing new calculations for para- and ortho-H2 high rotational collisional rate coefficients colliding with H2 (up to the maximum value for v = 0: J = 31), existing data for H2-H and H2-He collisions, and approximate scaling relations for missing collisional data, we investigate the excitation properties of H2 in a range of astrophysical environments, with the focus on PDRs (including benchmark PDR models and the Orion Bar). In these NLTE models, H2 emission is illustrated and shown as a diagnostic for physical conditions, such as temperature and density. Furthermore, we demonstrated the effect of updates in the collisional rates on the modeling results of H2 excitation. The resulting data sets of H2 collisional data should find wide application to other molecular environments.

Keywords: interstellar molecules; interstellar medium; photodissociation regions; astronomy databases
Dust Masses, Compositions, and Luminosities in the Nuclear Disks and the Diffuse Circumnuclear Medium of Arp 220

We present an analysis of the 4-2600 μm spectral energy distributions (SEDs) of the west and east nuclei and the diffuse infrared (IR) region of the merger-driven starburst Arp 220. We examine several possible source morphologies and dust temperature distributions using a mixture of silicate and carbonaceous grains. From fits to the SEDs we derive dust masses, temperatures, luminosities, and dust-inferred gas masses. We show that the west and east nuclei are powered by central sources deeply enshrouded behind $\sim {10}^{26}$ cm-2 column densities of hydrogen with an exponential density distribution, and that the west and east nuclei are optically thick out to wavelengths of ∼1900 and ∼770 μm, respectively. The nature of the central sources cannot be determined from our analysis. We derive star formation rates (SFRs) or black hole masses needed to power the IR emission, and show that the [C II] 158 μm line cannot be used as a tracer of the SFR in heavily obscured systems. Gas masses inferred from dust are larger than those inferred from CO observations, suggesting either larger dust-to-H mass ratios or the presence of hidden atomic H that cannot be inferred from CO observations. The luminosities per unit mass in the nuclei are ∼450 in solar units, smaller than the Eddington limit of ∼1000-3000 for an optically thick star-forming region, suggesting that the observed gas outflows are primarily driven by stellar winds and supernova shock waves instead of radiation pressure on the dust.

Keywords: astrophysical dust processes; silicate grains; interacting galaxies; ultraluminous infrared galaxies; carbonaceous grains; radiative processes; star formation; active galactic nuclei