adsabs/SciX_UAT_keywords huggingface dataset:
Using Multiple Emission Line Ratios to Constrain the Slope of the Dust Attenuation Law

We explore the possibility and practical limitations of using a three-line approach to measure both the slope and normalization of the dust attenuation law in individual galaxies. To do this, we focus on a sample of 11 galaxies with existing ground-based Balmer Hα and Hβ measurements from slit spectra, plus space-based grism constraints on Paschen-β. When accounting for observational uncertainties, we show that one galaxy has a well-constrained dust-law slope and normalization in the range expected from theoretical arguments; this galaxy therefore provides an example of what may be possible in the future. However, most of the galaxies are best fit by unusually steep or shallow slopes. We then explore whether additional astrophysical effects or observational biases could explain the elevated Paschen-β/Hα ratios driving these results. We find that galaxies with high Paschen-β/Hα ratios may be explained by slightly sub-unity covering fractions (>97%). Alternatively, differing slit losses for different lines can have a large impact on the results, emphasizing the importance of measuring all three lines with a consistent spectroscopic aperture. We conclude that, while the three-line approach to constraining the shape of the dust attenuation law in individual galaxies is promising, deep observations and a consistent observational strategy will be required to minimize observational biases and to disentangle the astrophysically interesting effect of differing covering fractions. The James Webb Space Telescope will provide more sensitive measurements of Balmer and Paschen lines for galaxies at z ≈ 0.3-2, enabling uniform constraints on the optical-infrared dust attenuation law and its intrinsic variation.

Keywords: interstellar dust extinction; interstellar dust; astrophysical dust processes; emission line galaxies; galaxies
Revisiting Galactic Disk and Spiral Arms Using Open Clusters

We use the largest catalog of open clusters in the post-Gaia era to provide an observational view of the Galactic disk. By compiling physical parameters such as age, distance, and kinematic information, we investigate the spatial distribution of open clusters and revisit the spiral arms and other asymmetries in the Galactic disk. Using young open clusters as a tracer of spiral arms, we map the spiral structure of the Galaxy and find that most of the clusters start migrating away from the spiral arms in about 10-20 Myr and fill the interarm regions as they age. Using the 3D kinematic information on 371 open star clusters, we derive different individual pattern speeds for spiral arms that closely follow the rotation curve of the Milky Way, hence favoring the transient nature of spiral arms in the Milky Way. The pattern rotation speeds of each spiral arm suggest that the spiral arms have not accelerated in the last 80 Myr. Based on the distribution of open clusters younger than 700 Myr above or below the Galactic plane, we found a solar offset of z ⊙ = 17.0 ± 0.9 pc north of the Galactic plane and estimated the scale height z h = 91.7 ± 1.9 pc from the Galactic plane.

Keywords: galaxy structure; milky way disk; open star clusters
Magnetohydrodynamic Accretion-Ejection: Jets Launched by a Nonisotropic Accretion-disk Dynamo. I. Validation and Application of Selected Dynamo Tensorial Components

Astrophysical jets are launched from strongly magnetized systems that host an accretion disk surrounding a central object. The origin of the jet-launching magnetic field is one of the open questions for modeling the accretion-ejection process. Here we address the question of how the accretion-disk magnetization and field structure required for jet launching are generated. Applying the PLUTO code, we present the first resistive magnetohydronamic simulations of jet launching including a nonscalar accretion-disk mean-field α2Ω dynamo in the context of large-scale disk-jet simulations. Essentially, we find the αφ-dynamo component determining the amplification of the poloidal magnetic field, which is strictly related to the disk magnetization (and, as a consequence, to the jet speed, mass, and collimation), while the αR- and αθ-dynamo components trigger the formation of multiple, antialigned magnetic loops in the disk, with strong consequences for the stability and dynamics of the disk-jet system. In particular, such loops trigger the formation of dynamo-inefficient zones, which are characterized by a weak magnetic field and therefore a lower value of the magnetic diffusivity. The jet mass, speed, and collimation are strongly affected by the formation of the dynamo-inefficient zones. Moreover, the θ component of the α dynamo plays a key role when the dynamo interacts with a nonradial component of the seed magnetic field. We also present correlations between the strength of the disk toy dynamo coefficients and the dynamical parameters of the jet that is launched.

Keywords: jets; high energy astrophysics; active galactic nuclei; magnetohydrodynamics; astrophysical fluid dynamics; plasma astrophysics; magnetohydrodynamical simulations; young stellar objects
Diffuse Light in Milky Way–like Haloes

We investigate the diffuse light (DL) content of dark matter haloes in the mass range $11.5\leqslant \mathrm{log}{M}_{\mathrm{halo}}\leqslant 13$ , a range that also includes the dark matter halo of the Milky Way, taking advantage of a state-of-the-art semianalytic model run on the merger trees extracted from a set of high-resolution cosmological simulations. The fraction of DL in such relatively small haloes is found to progressively decrease from the high- to the low-mass end, in good agreement with analytic and numerical results from simulations, and in good agreement also with the fraction of the DL observed in the Milky Way and M31. Haloes with different masses have different efficiencies in producing DL: $\mathrm{log}{M}_{\mathrm{halo}}\simeq 13$ is found to be the characteristic halo mass where the production of DL is the most efficient, while the overall efficiency decreases at both larger and smaller scales (this work). The DL content in this range of halo mass is the result of stellar stripping due to tidal interaction between satellites and their hosts (95%) and mergers between satellites and the central galaxy (5%), with preprocessed material, a subchannel of mergers and stripping, and so already included in the 100%, that contributes no more than 8% on average. The halo concentration is the main driver of the DL formation: more concentrated haloes have higher DL fractions that come from the stripping of more massive satellites in the high-halo-mass end, while dwarfs contribute mostly in the low-halo-mass end.

Keywords: galaxy formation; galaxy evolution
The Physical Properties of S0 Galaxy PGC 26218: The Origin of Starburst and Star Formation

We present 2D-spectroscopic observations from the Centro Astronómico Hispano Alemán 3.5 m telescope and millimeter observations from the NOrthern Extended Millimeter Array of the nearby S0 galaxy PGC 26218, which shows central star formation activity and post-starburst features in the disk. We estimate the star formation rate (SFR = 0.28 ± 0.01 M⊙ yr-1) and molecular gas mass ( $\mathrm{log}{M}_{{{\rm{H}}}_{2}}=7.60\pm 0.15\ {M}_{\odot }$ ) of PGC 26218 based on the extinction-corrected Hα emission line and the CO-H2 conversion factor (αCO) of the Milky Way, respectively. We find that PGC 26218 follows the star-forming main sequence (SFMS) and the Kennicutt-Schmidt law. Comparing the kinematics of CO(J = 1-0), stars, and Hα, we find that the rotational axis of CO(J = 1-0) is 45° different from that of Hα. In addition, the profile of the CO(J = 1-0) emission line shows asymmetry and has an inflow component of ∼46 km s-1. With the decomposition of the optical image, we confirm that PGC 26218 shows multiple nuclear structures. The projected offset between the most luminous optical center and the center of CO(J = 1-0) is 5"2 (∼0.6 kpc) and the latter overlaps with one of the optical cores. These results indicate that PGC 26218 may have experienced a gas-rich minor merger, extending its star formation and locating it in the SFMS.

Keywords: starburst galaxies; star formation; lenticular galaxies
Probing 3D Magnetic Fields Using Thermal Dust Polarization and Grain Alignment Theory

Magnetic fields are ubiquitous in the Universe and are thought to play an important role in various astrophysical processes. Polarization of thermal emission from dust grains aligned with the magnetic field is widely used to measure the 2D magnetic field projected onto the plane of the sky, but its component along the line of sight is not yet constrained. Here, we introduce a new method to infer 3D magnetic fields using thermal dust polarization and grain alignment physics. We first develop a physical model of thermal dust polarization using the modern grain alignment theory based on the magnetically enhanced radiative torque alignment theory. We then test this model with synthetic observations of magnetohydrodynamic simulations of a filamentary cloud with our updated POLARIS code. Combining the tested physical polarization model with synthetic polarization, we show that the B-field inclination angles can be accurately constrained by the polarization degree from synthetic observations. Compared to the true 3D magnetic fields, our method based on grain alignment physics is more accurate than the previous methods that assume uniform grain alignment. This new technique paves the way for tracing 3D B-fields using thermal dust polarization and grain alignment theory and for constraining dust properties and grain alignment physics.

Keywords: astrophysical dust processes; interstellar magnetic fields; interstellar dust; starlight polarization; star forming regions; star formation
Absolute Calibration. III. Improved Absolute Calibration for the Visible through the Mid-infrared

We propose Sirius as an improved zero-point-defining star and calibrate its spectrum to an accuracy of ~0.6% in both the visible and infrared. This result is based on a newly derived independent calibration in the visible of similar accuracy to the previous standard one, with which it is combined. We use a large variety of approaches in the infrared to reach about three times smaller error than for previous absolute calibrations. The results in the two wavelength regimes are in agreement, providing a consistent link from the visible throughout the near- and mid-infrared. The Sirius-based zero-point at 5557.5 Å (in vacuum) is 13.436 ± 0.081 × 10-12 W cm-2 μm-1, based on the improved value for Vega of 3.473 ± 0.018 × 10-12 W cm-2 μm-1 and the measured magnitude difference between the two stars. At 2.1603 μm, the zero-point is 4.225 ± 0.025 × 10-14 W cm-2 μm-1 taking Sirius at a magnitude of -1.395. A jackknife analysis indicates that there are no serious systematic errors in these results. We consider selection of secondary standards that can extend the calibration over the sky. Despite more than a century in this role, normal A-stars are not suitable, although Am and Ap stars may be. G-stars older than ~1 Gyr are good candidates if accurate temperatures can be measured. White dwarfs are suitable from the visible through the near-infrared, but their properties are unexplored at the necessary level at the longer infrared wavelengths, and for most facilities they are too faint there. Finally, as a further test of the calibration, we demonstrate an upgraded infrared flux method to determine accurate stellar diameters from K-band photometry.

Keywords: infrared photometry; calibration
ALMA CN Zeeman Observations of AS 209: Limits on Magnetic Field Strength and Magnetically Driven Accretion Rate

While magnetic fields likely play an important role in driving the evolution of protoplanetary disks through angular momentum transport, observational evidence of magnetic fields has only been found in a small number of disks. Although dust continuum linear polarization has been detected in an increasing number of disks, its pattern is more consistent with that from dust scattering than from magnetically aligned grains in the vast majority of cases. Continuum linear polarization from dust grains aligned to a magnetic field can reveal information about the magnetic field's direction, but not its strength. On the other hand, observations of circular polarization in molecular lines produced by Zeeman splitting offer a direct measure of the line-of-sight magnetic field strength in disks. We present upper limits on the net toroidal and vertical magnetic field strengths in the protoplanetary disk AS 209 derived from Zeeman splitting observations of the CN 2-1 line. The 3σ upper limit on the net line-of-sight magnetic field strength in AS 209 is 5.0 mG on the redshifted side of the disk and 4.2 mG on the blueshifted side of the disk. Given the disk's inclination angle, we set a 3σ upper limit on the net toroidal magnetic field strength of 8.7 and 7.3 mG for the red and blue sides of the disk, respectively, and 6.2 and 5.2 mG on the net vertical magnetic field on the red and blue sides of the disk. If magnetic disk winds are a significant mechanism of angular momentum transport in the disk, magnetic fields of a strength close to the upper limits would be sufficient to drive accretion at the rate previously inferred for regions near the protostar.

Keywords: protoplanetary disks; magnetic fields; stellar accretion disks
Photocleavage of Aliphatic C–C Bonds in the Interstellar Medium

Ultraviolet (UV) processing in the interstellar medium (ISM) induces the dehydrogenation of hydrocarbons. Aliphatics, including alkanes, are present in different interstellar environments, being prevalently formed in evolved stars; thus, the dehydrogenation by UV photoprocessing of alkanes plays an important role in the chemistry of the ISM, leading to the formation of unsaturated hydrocarbons and eventually to aromatics, the latter ubiquitously detected in the ISM. Here, through combined experimental results and ab initio calculations, we show that UV absorption (mainly at the Lyα emission line of hydrogen at 121.6 nm) promotes an alkane to an excited Rydberg state from where it evolves toward fragmentation, inducing the formation of olefinic C=C bonds, which are necessary precursors of aromatic hydrocarbons. We show that the photochemistry of aliphatics in the ISM does not primarily produce direct hydrogen elimination but preferential C–C photocleavage. Our results provide an efficient synthetic route for the formation of unsaturated aliphatics, including propene and dienes, and suggest that aromatics could be formed in dark clouds by a bottom-up mechanism involving molecular fragments produced by UV photoprocessing of aliphatics.

Keywords: astrochemistry; interstellar medium; dense interstellar clouds; laboratory astrophysics; molecular physics; interstellar dust processes; dust physics
Constraining the Quasar Radio-loud Fraction at z ∼ 6 with Deep Radio Observations

We carry out a series of deep Karl G. Jansky Very Large Array (VLA) S-band observations of a sample of 21 quasars at z ∼ 6. The new observations expand the searches of radio continuum emission to the optically faint quasar population at the highest redshift with rest-frame $4400\,\mathring{\rm A} $ luminosities down to $3\times {10}^{11}\ {L}_{\odot }$ . We report the detections of two new radio-loud quasars: CFHQS J2242+0334 (hereafter J2242+0334) at z = 5.88 and CFHQS J0227-0605 (hereafter J0227-0605) at z = 6.20, detected with 3 GHz flux densities of $87.0\pm 6.3\ \mu \mathrm{Jy}$ and $55.4\pm 6.7\ \mu \mathrm{Jy}$ , respectively. Their radio loudnesses are estimated to be 54.9 ± 4.7 and 16.5 ± 3.2, respectively. To better constrain the radio-loud fraction (RLF), we combine the new measurements with the archival VLA L-band data as well as available data from the literature, considering the upper limits for non-detections and possible selection effects. The final derived RLF is 9.4 ± 5.7% for the optically selected quasars at z ∼ 6. We also compare the RLF to that of the quasar samples at low redshift and check the RLF in different quasar luminosity bins. The RLF for the optically faint objects is still poorly constrained due to the limited sample size. Our results show no evidence of significant quasar RLF evolution with redshift. There is also no clear trend of RLF evolution with quasar UV/optical luminosity due to the limited sample size of optically faint objects with deep radio observations.

Keywords: high-redshift galaxies; quasars; radio continuum emission
The X-Ray Emission Reveals the Coronal Activities of Semi-detached Binaries

X-ray emission is an important tracer of stellar magnetic activity. We carried out a systematic correlation analysis for the X-ray luminosity $\mathrm{log}{L}_{{\rm{X}}}$ , bolometric luminosity $\mathrm{log}{L}_{\mathrm{bol}}$ , and X-ray activity level $\mathrm{log}({L}_{{\rm{X}}}$ /L bol) versus the binary parameters including orbital period P, Rossby number R O, effective temperature T eff, metallicity [Fe/H], the surface gravity $\mathrm{log}g$ , stellar mass M, and radius R, by assembling a large sample of semi-detached (EB-type) binaries with X-ray emission (EBXs). The fact that both $\mathrm{log}{L}_{{\rm{X}}}$ and $\mathrm{log}{L}_{\mathrm{bol}}$ change in accordance with $\mathrm{log}P$ indicates that X-ray emission originates from the convection zone, while $\mathrm{log}{L}_{{\rm{X}}}$ is proportional to the convection zone area. We found that EBXs with main-sequence components exhibit an upward and then a downward trend in both the $\mathrm{log}{T}_{\mathrm{eff}}$ – $\mathrm{log}{L}_{{\rm{X}}}$ and M– $\mathrm{log}{L}_{{\rm{X}}}$ relations, which is different from the monotonically decreasing trend shown by EBXs containing sub-giant and giant components. The magnetic activity level is negatively correlated with $\mathrm{log}{T}_{\mathrm{eff}}$ and stellar mass. Based on the magnetic dynamo model, the variations in the size and thickness of the surface convection zones can explain the observed relations. EBXs with main-sequence components have a similar R O– $\mathrm{log}({L}_{{\rm{X}}}/{L}_{\mathrm{bol}})$ relationship to that of the binaries in the clusters as Praesepe and Hyade. We compared the X-ray radiation properties of EBXs with those of the X-ray-emitting contact binaries and found that EBXs have broader value ranges for $\mathrm{log}{L}_{{\rm{X}}}$ and $\mathrm{log}({L}_{{\rm{X}}}$ /L bol).

Keywords: semi-detached binary stars; stellar activity; variable stars; beta lyrae stars; eclipsing binary stars; binary stars
Star-Galaxy Image Separation with Computationally Efficient Gaussian Process Classification

We introduce a novel method for discerning optical telescope images of stars from those of galaxies using Gaussian processes (GPs). Although applications of GPs often struggle in high-dimensional data modalities such as optical image classification, we show that a low-dimensional embedding of images into a metric space defined by the principal components of the data suffices to produce high-quality predictions from real large-scale survey data. We develop a novel method of GP classification hyperparameter training that scales approximately linearly in the number of image observations, which allows for application of GP models to large-size Hyper Suprime-Cam Subaru Strategic Program data. In our experiments, we evaluate the performance of a principal component analysis embedded GP predictive model against other machine-learning algorithms, including a convolutional neural network and an image photometric morphology discriminator. Our analysis shows that our methods compare favorably with current methods in optical image classification while producing posterior distributions from the GP regression that can be used to quantify object classification uncertainty. We further describe how classification uncertainty can be used to efficiently parse large-scale survey imaging data to produce high-confidence object catalogs.

Keywords: astronomy data analysis; astronomy data modeling; astronomical object identification
Oblique Electromagnetic Instabilities Driven by Pickup Ion Ring-beam Distributions in the Outer Heliosheath. II. Hybrid Simulations

Hybrid simulations are carried out to study the instabilities driven by the outer heliosheath pickup ions of ring-beam velocity distributions. Following the linear instability analysis in the companion paper, the electromagnetic instabilities at various propagation directions (0° ≤ θ ≤ 180°) are studied for pickup ion ring-beam distributions of different pickup angles (0° ≤ α ≤ 90°). Previous studies of the ring-beam pickup ion distributions have been limited to the parallel- and antiparallel-propagating modes (θ = 0° and 180°). In this paper, several one-dimensional hybrid simulations are performed to investigate the most unstable modes of different propagation angles predicted by the linear instability analysis. Moreover, two-dimensional hybrid simulations are conducted to examine the simultaneous excitation of the parallel, antiparallel, and oblique unstable modes and their role in the scattering of the outer heliosheath pickup ions. Our recent one-dimensional hybrid and particle-in-cell simulations with simulation domains along the background magnetic field demonstrated that at small pickup angles, the outer heliosheath pickup ions experience an incomplete scattering limited to the hemisphere of positive parallel velocities with respect to the background magnetic field. In contrast, the present two-dimensional hybrid simulation results show that when both parallel/antiparallel and oblique unstable modes are acting together, the pickup ions can be scattered into the hemisphere of negative parallel velocities and approach a near-isotropic velocity distribution. This is in conflict with the spatial retention scenario of the energetic neutral atom ribbon observed by the Interstellar Boundary Explorer, which requires pickup ions at small pickup angles to stream away from the ribbon directions.

Keywords: pickup ions; solar wind
Low-metallicity Young Clusters in the Outer Galaxy. III. Sh 2-127

In deep near-infrared imaging of the low-metallicity ([O/H] = -0.7 dex) H II region Sh 2-127 (S127) with Subaru/MOIRCS, we detected two young clusters with 413 members (S127A) in a slightly extended H II region and another with 338 members (S127B) in a compact H II region. The limiting magnitude was K = 21.3 mag (10σ), corresponding to a mass detection limit of ∼0.2 ${M}_{\odot }$ . These clusters are an order of magnitude larger than previously studied young low-metallicity clusters and larger than the majority of solar neighborhood young clusters. Fits to the K-band luminosity functions indicate very young cluster ages of 0.5 Myr for S127A and 0.1-0.5 Myr for S127B, consistent with the large extinction (up to AV ≃ 20 mag) from thick molecular clouds and the presence of a compact H II region and class I source candidates, and suggest that the initial mass function (IMF) of the low-metallicity clusters is indistinguishable from typical solar neighborhood IMFs. Disk fractions of 28% ± 3% for S127A and 40% ± 4% for S127B are significantly lower than those of similarly aged solar neighborhood clusters (∼50%-60%). The disk fraction for S127B is higher than those of previously studied low-metallicity clusters (<30%), probably due to S127B's age. This suggests that a large fraction of very young stars in low-metallicity environments have disks, but the disks are lost on a very short timescale. These results are consistent with our previous studies of low-metallicity star-forming regions, suggesting that a solar neighborhood IMF and low disk fraction are typical characteristics for low-metallicity regions, regardless of cluster scales.

Keywords: galaxy abundances; infrared sources; open star clusters; metallicity; protoplanetary disks; star formation; pre-main sequence; h ii regions