adsabs/SciX_UAT_keywords huggingface dataset:
Sp1149. II. Spectroscopy of H II Regions near the Critical Curve of MACS J1149 and Cluster Lens Models

Galaxy-cluster gravitational lenses enable the study of faint galaxies even at large lookback times, and, recently, time-delay constraints on the Hubble constant. There have been few tests, however, of lens model predictions adjacent to the critical curve (≲8″) where the magnification is greatest. In a companion paper, we use the GLAFIC lens model to constrain the Balmer L–σ relation for H II regions in a galaxy at redshift z = 1.49 strongly lensed by the MACS J1149 galaxy cluster. Here we perform a detailed comparison between the predictions of 10 cluster lens models that employ multiple modeling assumptions with our measurements of 11 magnified, giant H II regions. We find that that the models predict magnifications an average factor of 6.2 smaller, a ∼2σ tension, than that inferred from the H II regions under the assumption that they follow the low-redshift L–σ relation. To evaluate the possibility that the lens model magnifications are strongly biased, we next consider the flux ratios among knots in three images of Sp1149, and find that these are consistent with model predictions. Moreover, while the mass-sheet degeneracy could in principle account for a factor of ∼6 discrepancy in magnification, the value of H 0 inferred from SN Refsdal's time delay would become implausibly small. We conclude that the lens models are not likely to be highly biased, and that instead the H II regions in Sp1149 are substantially more luminous than the low-redshift Balmer L–σ relation predicts.

Keywords: gravitational lensing; strong gravitational lensing; h ii regions; galaxy clusters; galaxies; galaxy spectroscopy; high-redshift galaxies
Linear and Nonlinear Effects of Proton Temperature Anisotropy on Proton-beam Instability in the Solar Wind

Solar wind observations have shown that the drift velocity of the proton beam relative to the background proton is of the order of the local Alfvén velocity. The proton-beam instability has been suggested to play an important role in decelerating proton beams. Most existing studies examined the kinetic properties of the proton-beam instability in simple Maxwellian or drift-Maxwellian plasmas. In this paper, we systemically investigate the effects of the proton temperature anisotropy on the growth rates of proton-beam instabilities using linear Vlasov equations and the nonlinear evolution of these instabilities at different propagation angles using 1D and 2D hybrid simulations. The results show that the real frequencies, growth rates, and threshold conditions strongly depend on the proton temperature anisotropy ${T}_{i\perp }/{T}_{i| | }$ and the parallel proton beta ${\beta }_{i| | }$ . The parallel magnetosonic/whistler (M/W), backward M/W, and oblique Alfvén/ion-cyclotron (A/IC) instabilities are likely to grow in the regime of ${T}_{i\perp }/{T}_{i| | }\lt 1$ , whereas the parallel M/W, oblique A/IC, parallel A/IC, and mirror instabilities tend to be excited in the regime of ${T}_{i\perp }/{T}_{i| | }\gt 1$ . Moreover, the oblique A/IC instability with a linear wave growth phase can quickly reduce the proton-beam drift velocity when ${T}_{i\perp }/{T}_{i| | }\lt 1$ , while the nonlinear wave-particle interaction for the parallel A/IC and mirror instabilities tends to gradually reduce the drift velocity when ${T}_{i\perp }/{T}_{i| | }\gt 1$ . The linear and nonlinear evolution of the proton-beam instability associated with the proton temperature anisotropy can be used to explain the observed dependence of the proton-beam drift velocity on the plasma beta and temperature anisotropy in the solar wind.

Keywords: solar wind; space plasmas; alfven waves
Revisiting the Gas-phase Chemical Rate Coefficients at High Temperatures in CLOUDY

A two-body gas-phase reaction rate coefficient can be given by the usual Arrhenius-type formula which depends on temperature. The UMIST Database for Astrochemistry is a widely used database for reaction rate coefficients. They provide fittings for coefficients valid over a particular range of temperatures. The permissible upper-temperature limits vary over a wide range: from 100 to 41,000 K. A wide range of temperatures occurs in nature; thus, it requires evaluating the rate coefficients at temperatures outside the range of validity. As a result, a simple extrapolation of the rate coefficients can lead to unphysically large values at high temperatures. These result in unrealistic predictions. Here we present a solution to prevent the gas-phase reaction coefficients from diverging at a very high temperature. We implement this into the spectral synthesis code CLOUDY which operates over a wide range of temperatures from CMB to 1010 K subject to different astrophysical environments.

Keywords: reaction rates; astrochemistry; interstellar medium; interstellar molecules
Evidence for Proton Acceleration up to TeV Energies Based on VERITAS and Fermi-LAT Observations of the Cas A SNR

We present a study of γ-ray emission from the core-collapse supernova remnant Cas A in the energy range from 0.1 GeV to 10 TeV. We used 65 hr of the Very Energetic Radiation Imaging Telescope Array System (VERITAS) data to cover 200 GeV-10 TeV, and 10.8 yr of Fermi-Large Area Telescope (LAT) data to cover 0.1-500 GeV. The spectral analysis of Fermi-LAT data shows a significant spectral curvature around 1.3 ± 0.4stat GeV that is consistent with the expected spectrum from pion decay. Above this energy, the joint spectrum from Fermi-LAT and VERITAS deviates significantly from a simple power law, and it is best described by a power law with a spectral index of 2.17 ± 0.02stat and a cutoff energy of 2.3 ± 0.5stat TeV. These results, along with radio, X-ray, and γ-ray data, are interpreted in the context of leptonic and hadronic models. Assuming a one-zone model, we exclude a purely leptonic scenario and conclude that proton acceleration up to at least 6 TeV is required to explain the observed γ-ray spectrum. From modeling of the entire multiwavelength spectrum, a minimum magnetic field inside the remnant of Bmin ≈ 150 μG is deduced.

Keywords: gamma-ray astronomy; supernova remnants; galactic cosmic rays; ground-based astronomy; observational astronomy
The Phenomena of Flares and CMEs in the Sun and Stars: Why Are the Energy Upper Limits in Both Phenomena Comparable?

Solar/stellar flares which release large energies occur less frequently than those with small energies. Flare energies on a given star have not (yet) been observed to exceed E fm . Similarly, coronal mass ejections (CME's) with large kinetic energies (KE) on a given star also occur less frequently than those with small energies. The KE's of CME's on a given star have not (yet) been observed to exceed KE m . Interestingly, in any given star, E fm is found to be comparable in magnitude to KE m . This is puzzling since a one-to-one correlation between flares and CME's does not exist: some flares occur without any accompanying CME, and some CME's have no accompanying flare. Moreover, different types of MHD instabilities are believed to give rise to flares and CME's. The result E fm ≈ KE m could indicate support for Bemporad's conclusion: magnetic energy in the corona is in global equipartition with gravitational potential energy.

Keywords: solar flares; stellar flares
Star Formation in Splash Bridges

Splash bridges are created from the direct collision of two gas-rich disk galaxies. These direct collisions can eject gas masses on the order of 1010 M⊙ stripped from the stellar disks of each galaxy. The Taffy Galaxy system (UGC 1294/5) is a prototypical example of a splash bridge system. CO observations of the Taffy revealed that its splash bridge contains a mass of H2 equal to the Milky Way's H2 mass. However, the little visible star formation occurring within the bridge highlights the need for models of direct gas-rich disk collisions. The Arp 194 system displays what may be another splash bridge resulting from the collision between two disk galaxies. The region between the two stellar disks contains bright clumps of active star formation. We aim to better understand the conditions for star formation in splash bridges by employing a Jeans criterion to determine where gravitational instabilities occur in the shocked and cooling gas of gas-rich disk collisions. The splash bridge results are obtained from our previous work using a sticky particle code and post-processed. We find that the inclination between the gas disks and the collision velocity with which the gas collides strongly affects the fraction of gas that will become gravitationally unstable. Low inclinations between gas disks produce starbursts whereas high inclinations result in steady-rate star formation. The offset of the gas disks at impact will determine how many gas elements directly collide but does not strongly affect the resulting star formation.

Keywords: interacting galaxies; galaxy collisions; galaxy mergers; astronomical models; star formation; galaxy dynamics; hydrodynamics; hydrodynamical simulations; intergalactic gas
Exploring the Energy-dependent Radiation Properties in Dissipative Magnetospheres with Fermi Pulsars

The equatorial current sheets outside the light cylinder (LC) are thought to be promising sites of high-energy emission based on the results of recent numerical simulations. We explore the pulsar light curves and energy spectra by computing the curvature radiation based on the FIDO magnetospheres. The FIDO magnetospheres with a near force-free regime inside the LC and a finite but high conductivity outside the LC are constructed using a spectral algorithm. The pulsar high-energy emission properties are explored by integrating the trajectories of the test particles under the influence of both the accelerating electric field and the curvature radiation losses. As an application, we compare the predicted energy-dependent light curves and energy spectra with those of the Crab and Vela pulsars published in the Fermi 2PC catalog. We find that the observed characteristics of the light curves and energy spectra from the Crab and Vela pulsars can be well reproduced by the FIDO model.

Keywords: neutron stars; rotation powered pulsars; magnetohydrodynamical simulations
Transport of High-energy Charged Particles through Spatially Intermittent Turbulent Magnetic Fields

Identifying the sources of the highest energy cosmic rays requires understanding how they are deflected by the stochastic, spatially intermittent intergalactic magnetic field. Here we report measurements of energetic charged-particle propagation through a laser-produced magnetized plasma with these properties. We characterize the diffusive transport of the particles experimentally. The results show that the transport is diffusive and that, for the regime of interest for the highest energy cosmic rays, the diffusion coefficient is unaffected by the spatial intermittency of the magnetic field.

Keywords: high energy astrophysics; ultra-high-energy cosmic radiation; magnetic fields; laboratory astrophysics; plasma astrophysics; intergalactic medium; particle astrophysics
Galactic Cosmic Rays, Cosmic-Ray Variations, and Cosmogenic Nuclides in Meteorites

We present a new generation of model calculations for cosmogenic production rates in various types of solar system bodies. The model is based on the spectra for primary and secondary particles calculated using the INCL++6 code, which is the most reliable and most sophisticated code available for spallation reactions. Thanks to the recent improvements (extending the code to lower and higher energies and considering light charged particles as ejectiles and projectiles), we can for the first time directly consider primary and secondary Galactic α particles. We calculate production rates for 22Na, 10Be, and 26Al in an L-chondrite with a radius of 45 cm and in the Apollo 15 drill core, and we determine the long-term average Galactic cosmic-ray (GCR) spectrum (represented by the solar modulation potential Φ) in the meteoroid orbits at ∼3 au of Φ = 600 MV and at 1 au, i.e., for Earth and Moon of Φ = 660 MV. From this, we calculate a long-term average GCR gradient in the inner solar system of ∼5% au-1. Finally, we discuss the possibility of studying temporal GCR variations and meteoroid orbits using production rate ratios of short- and long-lived radionuclides.

Keywords: galactic cosmic rays; meteorites; heliosphere; the moon
Radiative Transfer in Lyα Nebulae. I. Modeling a Continuous or Clumpy Spherical Halo with a Central Source

To understand the mechanism behind high-z Lyα nebulae, we simulate the scattering of Lyα in a H I halo about a central Lyα source. For the first time, we consider both smooth and clumpy distributions of halo gas, as well as a range of outflow speeds, total H I column densities, H I spatial concentrations, and central source galaxies (e.g., with Lyα line widths corresponding to those typical of active galactic nucleus or star-forming galaxies). We compute the spatial-frequency diffusion and the polarization of the Lyα photons scattered by atomic hydrogen. Our scattering-only model reproduces the typical size of Lyα nebulae (~100 kpc) at total column densities N H I ≥ 1020 cm-2 and predicts a range of positive, flat, and negative polarization radial gradients. We also find two general classes of Lyα nebula morphologies: with and without bright cores. Cores are seen when N H I is low, i.e., when the central source is directly visible, and are associated with a polarization jump, a steep increase in the polarization radial profile just outside the halo center. Of all the parameters tested in our smooth or clumpy medium model, N H I dominates the trends. The radial behaviors of the Lyα surface brightness, spectral line shape, and polarization in the clumpy model with covering factor f c ≳ 5 approach those of the smooth model at the same N H I. A clumpy medium with high N H I and low f c ≲ 2 generates Lyα features via scattering that the smooth model cannot: a bright core, symmetric line profile, and polarization jump.

Keywords: radiative transfer; radiative transfer simulations; lyman-alpha galaxies; emission nebulae
An Hα Impression of Lyα Galaxies at z ≃ 6 with Deep JWST/NIRCam Imaging

We present a study of seven spectroscopically confirmed (Lyα-emitting) galaxies at redshift z ≃ 6 using the JWST/NIRCam imaging data. These galaxies, with a wide range of Lyα luminosities, were recently observed in a series of NIRCam broad and medium bands. We constrain the rest-frame UV/optical continua and measure the Hα line emission of the galaxies using the combination of JWST/NIRCam and archival HST/WFC3 infrared photometry. We further estimate the escape fractions of their Lyα photons ( ${f}_{\mathrm{esc}}^{\mathrm{Ly}\alpha }$ ) and the production efficiency of ionizing photons (ξ ion). Among the sample, six out of seven galaxies have Lyα escape fractions of ≲10%, which might be the status for most of the star-forming galaxies at z ≃ 6. One UV-faint Lyα galaxy with an extremely blue UV slope has a large value of ${f}_{\mathrm{esc}}^{\mathrm{Ly}\alpha }$ reaching ≃50%. These galaxies have a broad range of ξ ion over log10 ξ ion,0 (Hz erg‑1) ∼ 25.0–26.5. We find that UV-fainter galaxies with bluer UV-continuum slopes likely have higher escape fractions of Lyα photons. We also find that galaxies with higher Lyα line emission tend to produce ionizing photons more efficiently. The most Lyα-luminous galaxy in the sample has a very high ξ ion,0 of log10 ξ ion,0 (Hz erg‑1) > 26. Our results support the scenario that Lyα galaxies may have served as an important contributor to cosmic reionization. Blue and bright Lyα galaxies are excellent targets for JWST follow-up spectroscopic observations.

Keywords: high-redshift galaxies; lyman-alpha galaxies; galaxy properties; reionization; james webb space telescope
Strong Soft X-Ray Excess in 2015 XMM-Newton Observations of BL Lac OJ 287

We report a strong soft X-ray excess in the BL Lacartae γ-ray blazar OJ 287 during long exposure in 2015 May, among two of the latest XMM-Newton observations performed in 2015 and 2018 May. In the case of the 2015 May observation, a log parabola model fits the EPIC-pn data well, while a log parabola plus a power law describes the overall simultaneous optical to X-ray spectra, suggesting the excess as the synchrotron tail. This interpretation, however, is inconsistent with the observed spectral break between near-infrared (NIR) and optical spectra, attributed to a standard disk around a supermassive black hole (SMBH). Based on this, we considered two commonly invoked accretion-disk-based models in active galactic nuclei (AGNs) to explain the soft excess: the cool Comptonization component in the accretion disk and the blurred reflection from the partially ionized accretion disk. We found that both cool Comptonization and blurred reflection models provide an equally good fit to the data, and favor a super-heavy SMBH of mass ∼1010 M⊙. Further investigation of about a month-long simultaneous X-ray and ultraviolet (UV) pointing observations revealed a delayed UV emission with respect to the 1.5-10 keV band, favoring X-ray reprocessing phenomenon as the dominant mechanism. The results suggest that the soft excess is probably caused by strong light bending close to the SMBH. The detected soft excess in the 2015 data and its disappearance in the 2018 data is also consistent with the presence of accretion-disk emission, inferred from the NIR-optical spectral break between 2013 May and 2016 March.

Keywords: galaxy nuclei; x-ray active galactic nuclei; active galaxies; high energy astrophysics; galaxy jets; relativistic disks; blazars; bl lacertae objects; supermassive black holes
Massive Star Formation in the Tarantula Nebula

In this work, we present 299 candidate young stellar objects (YSOs) in 30 Doradus discovered using Spitzer and Herschel point-source catalogs, 276 of which are new. We study the parental giant molecular clouds in which these YSO candidates form using recently published Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 7 observations of 12CO and 13CO. The threshold for star formation in 30 Doradus inferred by the LTE-based mass surface density is 178 M ⊙ pc-2, 40% higher than the threshold for star formation in the Milky Way. This increase in star formation threshold in comparison to the Milky Way and increase in line width seen in clumps 11 pc away in comparison to clumps 45 pc away from the R136 super star cluster could be due to injected turbulent energy, increase in interstellar medium pressure, and/or local magnetic field strength. Of the 299 YSO candidates in this work, 62% are not associated with 12CO molecular gas. This large fraction can be explained by the fact that 75%-97% of the H2 gas is not traced by CO. We fit a Kroupa initial mass function to the YSO candidates and find that the total integrated stellar mass is 18,000 M ⊙ and that the region has a star formation rate (SFR) of 0.18 M ⊙ yr-1. The initial mass function determined here applies to the four 150″ × 150″ (37.5 pc × 37.5 pc) subfields and one 150″ × 75″ (37.5 pc × 18.8 pc) subfield observed with ALMA. The SFR in 30 Doradus has increased in the past few million years.

Keywords: star formation; interstellar medium; young stellar objects
The Recent LMC-SMC Collision: Timing and Impact Parameter Constraints from Comparison of Gaia LMC Disk Kinematics and N-body Simulations

We present analysis of the proper-motion (PM) field of the red clump stars in the Large Magellanic Cloud (LMC) disk using the Gaia Early Data Release 3 catalog. Using a kinematic model based on old stars with 3D velocity measurements, we construct the residual PM field by subtracting the center-of-mass motion and internal rotation motion components. The residual PM field reveals asymmetric patterns, including larger residual PMs in the southern disk. Comparisons of the observed residual PM field with those of five numerical simulations of an LMC analog that is subject to the tidal fields of the Milky Way and the Small Magellanic Cloud (SMC) show that the present-day LMC is not in dynamical equilibrium. We find that both the observed level of disk heating (PM residual rms of 0.057 ± 0.002 mas yr-1) and kinematic asymmetry are not reproduced by Milky Way tides or if the SMC impact parameter is larger than the size of the LMC disk. This measured level of disk heating provides a novel and important method to validate numerical simulations of the LMC-SMC interaction history. Our results alone put constraints on an impact parameter ≲10 kpc and impact timing <250 Myr. When adopting the impact timing constraint of ~140-160 Myr ago from previous studies, our results suggest that the most recent SMC encounter must have occurred with an impact parameter of ~5 kpc. We also find consistent radial trends in the kinematically and geometrically derived disk inclination and line-of-node position angles, indicating a common origin.

Keywords: large magellanic cloud; interacting galaxies; stellar kinematics; small magellanic cloud; proper motions; dwarf galaxies; hydrodynamical simulations
Tracing the Galactic Disk with the Kinematics of Gaia Cepheids

Classical Cepheids (CCs) are excellent tracers for understanding the structure of the Milky Way disk. The latest Gaia Data Release 3 provides a large number of line-of-sight velocity information for Galactic CCs, offering an opportunity for studying the kinematics of the Milky Way. We determine the 3D velocities of 2057 CCs relative to the Galactic center. From the projections of the 3D velocities onto the X–Y plane of the Galactic disk, we find that the V R and V ϕ velocities of the northern and southern warps (directions with highest amplitude) are different. This phenomenon may be related to warp precession or asymmetry in warp structure. By investigating the kinematic warp model, we find that the vertical velocities of CCs are more suitable for constraining the warp precession rate than the line-of-node angle. Our results suggest that CCs at 12–14 kpc are the best sample for determining the Galactic warp precession rate. Based on the spatial structure parameters of Cepheid warp from Chen et al., we determine a warp precession rate of ω = 4.9 ± 1.6 km s‑1 kpc‑1 at 13 kpc, which supports a low precession rate in the warp model. In the future, more kinematic information on CCs will help to constrain the structure and evolution of the Milky Way better.

Keywords: galaxy structure; milky way disk; stellar kinematics; galaxy rotation curves; cepheid variable stars
HD 63021: Chromospheric Activity and Mass Transfer in a Close Binary

Prompted by X-ray detections from multiple surveys, we investigated the A-type star HD 63021 and found that it is a double-lined spectroscopic binary with highly variable emission associated with the primary star. Analysis of our multiepoch spectroscopic observations, the majority of which were carried out on small-aperture telescopes, indicates a very short orbital period of just 2.9 days and a mass ratio M2/M1 of 0.23. The A1 V star is a slow rotator, with a rotational speed of ∼34 km s-1. Assuming that its mass is 2.3 M⊙, the present-day secondary is an evolved star of ∼0.5 M⊙ that nearly fills its Roche lobe. This secondary star rotates comparatively rapidly at ∼44 km s-1, and we see evidence that it is chromospherically active. Analysis of a photometric light curve from TESS reveals two strong periods, one at the orbital period for the system and another at half the orbital period. These findings suggest that HD 63021 is a close binary system undergoing mass transfer from the secondary star onto the primary star—in all ways like an Algol eclipsing binary system, except without the eclipse. We discuss the system's mass transfer, which is not steady but seems to run in fits and bursts, and infer the system's basic physical properties from an orbital parameter study, the Roche lobe geometry, and its extant X-ray emission.

Keywords: ae stars; algol variable stars; close binary stars; x-ray binary stars; spectroscopy; spectral energy distribution; orbit determination; stellar classification; stellar rotation; time domain astronomy; variable stars