Sazuna/UAT_keywords huggingface dataset:
Dynamic Responses of Radiation Belt Electron Fluxes to Magnetic Storms and their Correlations with Magnetospheric Plasma Wave Activities. To investigate the responses of Earth's radiation belt electrons during magnetic storms and their correlations with magnetospheric chorus and plasmaspheric hiss waves, a statistical analysis is conducted using high-quality Van Allen Probes measurements during 68 isolated geomagnetic storms from 2012 September to 2017 December. The variations of radiation belt electron fluxes exhibit high dependence on electron kinetic energy, L-shell, and geomagnetic storm magnitude. It is found that the Increase-type events increase considerably with L-shell at L ∼ 3.0-5.0, the Decrease-type events tend to occur more frequently at L = 3.7-4.7 for &lt;1 MeV electrons during weak storms and at L = 3.5-6 for &gt;1 MeV electrons during moderate storms, and the No-change-type storm events are relatively dominant for extremely high-energy (&gt;5.2 MeV) electrons. Superposed epoch analyses for the three types of storm events indicate that compared to relativistic (604 keV) electrons, ultrarelativistic (3.4 MeV) electron flux enhancements are more likely in association with elevated solar wind pressure during the storm initial phase, enhanced southward initial mass function Bz during the storm main phase, and prolonged high solar wind speed during the storm recovery phase. It is also shown that the dynamic variations of relativistic (604 keV) electron fluxes are closely connected to the activity level of chorus waves, but the three variation categories of ultrarelativistic (3.4 MeV) electrons have basically comparable intensities of chorus waves possibly due to the loss mechanisms becoming more dominate for their No-change-type or Decrease-type events. From a statistically observational perspective, chorus waves act as a critical candidate for relativistic electron acceleration and plasmaspheric hiss as a viable cause for relativistic electron loss.

Keywords: Plasmapause, Van Allen radiation belts, Solar wind, Solar storm, Interplanetary physics
A Transition of Dynamo Modes in M Dwarfs: Narrowing Down the Spectral Range Where the Transition Occurs. Houdebine et al. combined Ca II data with projected rotational velocities (V sin I) to construct rotation-activity correlations (RAC) in K-M dwarfs. The RAC slopes were used to argue that a transition between dynamo modes occurs at a spectral type between M2 and M3. H17 suggested that the dynamo transition corresponds to a transition to complete convection (TTCC). An independent study of GAIA data led Jao et al. to suggest that the TTCC sets in "near M3.0V," close to the H17 result. However, the changes in a star that cause TTCC signatures in GAIA data might not lead to changes in Ca II emission at an identical spectral type: the latter are also affected by magnetic effects, which depend on certain properties of convection in the core. Here, we use Ca II emission fluxes in a sample of ∼600 M dwarfs, and attempt to narrow down the transition from one dynamo mode to another: rather than relying on RAC slopes, we quantify how the Ca II emission flux varies with spectral type to identify "steps" where the flux decreases significantly across a narrow range of spectral types. We suggest that the dynamo mode transition may be narrowed down to between M2.1 and M2.3. This is close to, but earlier than, the TTCC location identified by Jao et al. We suggest that the transition in dynamo mode may be related to the existence of a small convective core, which occurs for a finite time interval in certain low-mass stars.

Keywords: Stellar chromospheres, Astrophysical processes
Velocity Dispersions of Brightest Cluster Galaxies and Their Host Clusters. We explore connections between brightest cluster galaxies (BCGs) and their host clusters. We first construct a HeCS-omnibus cluster sample including 227 galaxy clusters within 0.02 &lt; z &lt; 0.30; the total number of spectroscopic members from MMT/Hectospec and SDSS observations is 52325. Taking advantage of the large spectroscopic sample, we compute physical properties of the clusters including the dynamical mass and cluster velocity dispersion (σcl). We also measure the central stellar velocity dispersion of the BCGs (σ*,BCGs) to examine the relation between BCG velocity dispersion and cluster velocity dispersion for the first time. The observed relation between BCG velocity dispersion and the cluster velocity dispersion is remarkably tight. Interestingly, the σ*,BCG/σcl ratio decreases as a function of σcl unlike the prediction from the numerical simulation of Dolag et al. The trend in σ*,BCG/σcl suggests that BCG formation is more efficient in lower mass halos.

Keywords: Galaxy clusters, Brightest cluster galaxies, Galaxy dark matter halos, Redshift surveys
On the Energetics of a Possible Relativistic Jet Associated with the Binary Neutron Star Merger Candidate S190425z. Advanced LIGO and Virgo (AdvLIGO/VIRGO) detectors reported the first binary neutron star merger candidate in the third observing run, S190425z, on 2019 April 25. A weak γ-ray excess was reported nearly coincidentally by the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) satellite, which accidentally covered the entire localization region of AdvLIGO/VIRGO. Electromagnetic follow-up in longer wavelengths has not lead to the detection of any associated counterparts. Here we combine the available information from gravitational wave measurements and upper limits of fluence from INTEGRAL to show that the observations are completely consistent with a relativistic Gaussian structured jet and a typical short duration gamma-ray burst (GRB) being produced in the merger. We obtain posterior bounds on the on-axis isotropic equivalent energy of the associated GRB under different prior distributions. This study demonstrates that even limited gravitational wave and electromagnetic information could be combined to produce valuable insights about outflows from mergers. Future follow-ups may help constrain the jet structure further, especially if there is an orphan afterglow detection associated with the candidate.

Keywords: Gravitational wave sources
How Efficient Is the Streaming Instability in Viscous Protoplanetary Disks?. The streaming instability is a popular candidate for planetesimal formation by concentrating dust particles to trigger gravitational collapse. However, its robustness against the physical conditions expected in protoplanetary disks is unclear. In particular, particle stirring by turbulence may impede the instability. To quantify this effect, we develop the linear theory of the streaming instability with external turbulence modeled by gas viscosity and particle diffusion. We find the streaming instability is sensitive to turbulence, with growth rates becoming negligible for alpha viscosity parameters α ≳ St1.5, where St is the particle Stokes number. We explore the effect of nonlinear drag laws, which may be applicable to porous dust particles, and find growth rates are modestly reduced. We also find that gas compressibility increases growth rates by reducing the effect of diffusion. We then apply the linear theory to global models of viscous protoplanetary disks. For minimum-mass solar nebula disk models, we find the streaming instability only grows within disk lifetimes beyond tens of astronomical units, even for centimeter-sized particles and weak turbulence (α ∼ 10-4). Our results suggest it is rather difficult to trigger the streaming instability in nonlaminar protoplanetary disks, especially for small particles.

Keywords: Planetary theory, Planet formation, Exoplanet formation, Hydrodynamics
Chandra Observations of NGC 7212: Large-scale Extended Hard X-Ray Emission. Recent observations of nearby Compton thick (CT) active galactic nuclei (AGNs) with Chandra have resolved hard (&gt;3 keV) X-ray emission extending out from the central supermassive black hole to kiloparsec scales, challenging the long-held belief that the characteristic hard X-ray continuum and fluorescent Fe K lines originate in the inner ∼parsec due to the excitation of obscuring material. In this paper we present the results of the most recent Chandra ACIS-S observations of NGC 7212, a CT AGN in a compact group of interacting galaxies, with a total effective exposure of ∼150 ks. We find ∼20% of the observed emission is found outside of the central kiloparsec, with ∼17% associated with the soft X-rays, and ∼3% with hard X-ray continuum and Fe K line. This emission is extended both along the ionization cone and in the cross-cone direction up to ∼3.8 kpc scales. The spectrum of NGC 7212 is best represented by a mixture of thermal and photoionization models that indicate the presence of complex gas interactions. These observations are consistent with what is observed in other CT AGN (e.g., ESO 428-G014, NGC 1068), providing further evidence that this may be a common phenomenon. High-resolution observations of extended CT AGN provide an especially valuable environment for understanding how AGN feedback impacts host galaxies on galactic scales.

Keywords: AGN host galaxies, Active galaxies, X-ray active galactic nuclei
Two-year Cosmology Large Angular Scale Surveyor (CLASS) Observations: 40 GHz Telescope Pointing, Beam Profile, Window Function, and Polarization Performance. The Cosmology Large Angular Scale Surveyor (CLASS) is a telescope array that observes the cosmic microwave background (CMB) over 75% of the sky from the Atacama Desert, Chile, at frequency bands centered near 40, 90, 150, and 220 GHz. CLASS measures the large angular scale (1° ≲ θ ≤ 90°) CMB polarization to constrain the tensor-to-scalar ratio at the r ∼ 0.01 level and the optical depth to last scattering to the sample variance limit. This paper presents the optical characterization of the 40 GHz telescope during its first observation era, from 2016 September to 2018 February. High signal-to-noise observations of the Moon establish the pointing and beam calibration. The telescope boresight pointing variation is &lt;0°023 (&lt;1.6% of the beam's full width at half maximum (FWHM)). We estimate beam parameters per detector and in aggregate, as in the CMB survey maps. The aggregate beam has an FWHM of 1°579 ± 0°001 and a solid angle of 838 ± 6 μsr, consistent with physical optics simulations. The corresponding beam window function has a sub-percent error per multipole at ℓ &lt; 200. An extended 90° beam map reveals no significant far sidelobes. The observed Moon polarization shows that the instrument polarization angles are consistent with the optical model and that the temperature-to-polarization leakage fraction is &lt;10-4 (95% C.L.). We find that the Moon-based results are consistent with measurements of M42, RCW 38, and Tau A from CLASS's CMB survey data. In particular, Tau A measurements establish degree-level precision for instrument polarization angles.

Keywords: Early universe, Cosmic microwave background radiation, Observational cosmology, The Moon, Astronomical instrumentation, Polarimeters
The ALMA Spectroscopic Survey in the HUDF: A Model to Explain Observed 1.1 and 0.85 mm Dust Continuum Number Counts. We present a new semiempirical model for the dust continuum number counts of galaxies at 1.1 mm and 850 μm. Our approach couples an observationally motivated model for the stellar mass and star formation rate distribution of galaxies with empirical scaling relations to predict the dust continuum flux density of these galaxies. Without a need to tweak the IMF, the model reproduces the currently available observations of the 1.1 mm and 850 μm number counts, including the observed flattening in the 1.1 mm number counts below 0.3 mJy and the number counts in discrete bins of different galaxy properties. Predictions of our work include the following: (1) the galaxies that dominate the number counts at flux densities below 1 mJy (3 mJy) at 1.1 mm (850 μm) have redshifts between z = 1 and z = 2, stellar masses of ∼5 × 1010 M⊙, and dust masses of ∼108 M⊙; (2) the flattening in the observed 1.1 mm number counts corresponds to the knee of the 1.1 mm luminosity function. A similar flattening is predicted for the number counts at 850 μm; (3) the model reproduces the redshift distribution of current 1.1 mm detections; and (4) to efficiently detect large numbers of galaxies through their dust continuum, future surveys should scan large areas once reaching a 1.1 mm flux density of 0.1 mJy rather than integrating to fainter fluxes. Our modeling framework also suggests that the amount of information on galaxy physics that can be extracted from the 1.1 mm and 850 μm number counts is almost exhausted.

Keywords: Galaxy formation, Dust continuum emission, Galaxy evolution, Interstellar medium, High-redshift galaxies
A Method to Distinguish Quiescent and Dusty Star-forming Galaxies with Machine Learning. Large photometric surveys provide a rich source of observations of quiescent galaxies, including a surprisingly large population at z &gt; 1. However, identifying large, but clean, samples of quiescent galaxies has proven difficult because of their near-degeneracy with interlopers such as dusty, star-forming galaxies. We describe a new technique for selecting quiescent galaxies based upon t-distributed stochastic neighbor embedding (t-SNE), an unsupervised machine-learning algorithm for dimensionality reduction. This t-SNE selection provides an improvement both over UVJ, removing interlopers that otherwise would pass color selection, and over photometric template fitting, more strongly toward high redshift. Due to the similarity between the colors of high- and low-redshift quiescent galaxies, under our assumptions, t-SNE outperforms template fitting in 63% of trials at redshifts where a large training sample already exists. It also may be able to select quiescent galaxies more efficiently at higher redshifts than the training sample.

Keywords: Computational astronomy, Quenched galaxies, Astronomy data analysis, Galaxy classification systems, Star formation, Galaxy quenching
A Systematic Study of the Dust of Galactic Supernova Remnants. I. The Distance and the Extinction. By combining the photometric, spectroscopic, and astrometric information of the stars in the sightline of supernova remnants (SNRs), the distances to and the extinctions of 32 Galactic SNRs are investigated. The stellar atmospheric parameters are from the Sloan Digital Sky Survey-DR14/Apache Point Observatory Galaxy Evolution Experiment and Large sky Area Multi-Object fiber Spectroscopic Telescope-DR5/LEGUE spectroscopic surveys. The multiband photometry, from optical to infrared, are collected from the Gaia, APASS, Pan-STARRS1, Two Micron All Sky Survey, and Wide-field Infrared Survey Explorer surveys. With the calibrated Gaia distances of individual stars, the distances to 15 of 32 SNRs are well determined from their produced extinction and association with molecular clouds. The upper limits of distance are derived for three SNRs. The color excess ratios E({g}P1-λ)/E({g}P1-{r}P1) of 32 SNRs are calculated, and their variation with wavebands is fitted by a simple dust model. The inferred dust grain size distribution bifurcates: while the graphite grains have comparable size to the average interstellar medium dust, the silicate grains are generally larger. Along the way, the average extinction law from optical to near-infrared of the Milky Way is derived from the 1.3-million-star sample and found to agree with the CCM89 law with RV=3.15.

Keywords: Supernova remnants, Extinction, Interstellar dust
Relationships between Photospheric Vertical Electric Currents and Hard X-Ray Sources in Solar Flares: Statistical Study. There are still debates over whether particle acceleration in solar flares may occur due to interruption of electric currents flowing along magnetic loops. To contribute to this debate, we performed the first statistical study of relationships between flare hard X-ray (HXR; 50-100 keV) sources observed by the Ramaty High-Energy Solar Spectroscopic Imager and photospheric vertical electric currents (PVECs, jr) calculated using vector magnetograms obtained with the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. We analyzed a sample of 48 flares from the C3.0 to X3.1 class and were observed in the central part of the solar disk by both instruments in 2010-2015. We found that ≈70% of all HXR sources overlapped with islands or ribbons of enhanced (| {j}r| &gt; {10}4 statampere cm-2) PVECs. However, less than ≈40% of the HXR sources overlapped with PVEC maxima, with an accuracy of ±3″. In more than half of the flares, there were HXR sources outside of regions of enhanced PVECs. We found no correlation between the intensity of the HXR sources and PVEC density or total PVEC under them. No systematic dissipation of PVECs under the HXR sources was found during the flares. Collectively, the results do not support the current-interruption flare models. However, the results indicate the importance of the presence of longitudinal currents in flare regions. To understand their specific role in the processes of energy release, plasma heating, and acceleration of particles requires further investigation.

Keywords: Solar active region magnetic fields, Solar flares, Solar photosphere, Solar x-ray flares, Solar chromosphere
Mass Bias of Weak-lensing Shear-selected Galaxy Cluster Samples. We estimate the Eddington bias on weak-lensing mass measurements of shear-selected galaxy cluster samples. The mass bias is expected to be significant because constructions of cluster samples from peaks in weak-lensing mass maps and measurements of cluster masses from their tangential shear profiles share the same noise. We quantify this mass bias from large sets of mock cluster samples with analytical density profiles and realistic large-scale structure noise from ray-tracing simulations. We find that, even for peaks with signal-to-noise ratio larger than 4.0 in weak-lensing mass maps constructed in a deep survey with a high source galaxy number density of 30 arcmin-2, derived weak-lensing masses for these shear-selected clusters are still biased high by ∼55% on average. Such a large bias mainly originates from upscattered low-mass objects, which is an inevitable consequence of selecting clusters with a noisy observable directly linked to the mass measurement. We also investigate the dependence of the mass bias on different physical and observational parameters, finding that the mass bias strongly correlates with cluster redshifts, true halo masses, and selection signal-to-noise thresholds, but having moderate dependence on observed weak-lensing masses and survey depths. This bias, albeit considerable, can still be modeled accurately in statistical studies of shear-selected clusters, as the intrinsic scatter around the mean bias is found to be reasonable in size. We demonstrate that such a bias can explain the deviation in X-ray properties previously found on a shear-selected cluster sample. Our result will be useful for turning large samples of shear-selected clusters available in future surveys into potential probes of cosmology and cluster astrophysics.

Keywords: Galaxy clusters, Observational cosmology, Weak gravitational lensing
Subaru Infrared Adaptive Optics-assisted High-spatial-resolution Imaging Search for Luminous Dual Active Galactic Nuclei in Nearby Ultraluminous Infrared Galaxies. We present infrared K'-band (2.1 μm) and L'-band (3.8 μm) high-spatial-resolution (&lt;0"3) imaging observations of 17 nearby (z &lt; 0.17) ultraluminous infrared galaxies (ULIRGs) assisted with the adaptive optics of the Subaru Telescope. We search for compact red K' - L' color emission as the indicator of luminous active galactic nuclei (AGNs) due to AGN-heated hot dust emission. Two luminous dual AGN candidates are revealed. Combining these results with those of our previous study, we can state that the detected fraction of luminous dual AGNs in nearby ULIRGs is much less than unity (&lt;20%), even when infrared wavelengths &gt;2 μm are used that should be sensitive to buried AGNs due to small dust extinction effects. For ULIRGs with resolved multiple nuclear K'-band emission, we estimate the activation of supermassive black holes (SMBHs) in individual galaxy nuclei in the form of AGN luminosity normalized by SMBH mass inferred from the stellar luminosity of the host galaxy. We confirm a trend that more massive SMBHs in K'-band brighter primary galaxy nuclei are generally more active, with higher SMBH-mass-normalized AGN luminosity, than less massive SMBHs in K'-band fainter secondary galaxy nuclei, as predicted by numerical simulations of gas-rich major galaxy mergers. In two sources, the presence of even infrared-elusive extremely deeply buried AGNs is indicated by comparisons with available (sub)millimeter data. Non-synchronous SMBH activation (I.e., less activation of less massive SMBHs) and the possible presence of such infrared-elusive AGNs may be responsible for the small fraction of infrared-detected luminous dual AGNs in nearby merging ULIRGs.

Keywords: Supermassive black holes, Active galactic nuclei, Galaxy mergers, Ultraluminous infrared galaxies, Near infrared astronomy
Revising Natal Kick Prescriptions in Population Synthesis Simulations. Natal kicks are a matter of debate and they significantly affect the merger rate density of compact objects. Here, we present a new simple formalism for natal kicks of neutron stars (NSs) and black holes (BHs). We describe the magnitude of the kick as {V}kick∝ {f}H05 mej mrem-1, where fH05 is a normalization factor, drawn from a Maxwellian distribution with one-dimensional rms velocity σ = 265 km s-1, mej is the mass of the supernova (SN) ejecta, and mrem is the mass of the compact object. This formalism matches the proper motions of young Galactic pulsars and can naturally account for the differences between core-collapse SNe of single stars, electron-capture SNe and ultra-stripped SNe occurring in interacting binaries. Finally, we use our new kick formalism to estimate the local merger rate density of binary NSs (RBNS), BH-NS binaries (RBHNS), and binary BHs (RBBH), based on the cosmic star formation rate density and metallicity evolution. In our fiducial model, we find RBNS ∼ 600 Gpc-3 yr-1, RBHNS ∼ 10 Gpc-3 yr-1, and RBBH ∼ 50 Gpc-3 yr-1, fairly consistent with the numbers inferred from the LIGO-Virgo collaboration.

Keywords: Gravitational waves, Binary stars, Supernovae, Black holes
Cosmic-Ray Anisotropies in Right Ascension Measured by the Pierre Auger Observatory. We present measurements of the large-scale cosmic-ray (CR) anisotropies in R.A., using data collected by the surface detector array of the Pierre Auger Observatory over more than 14 yr. We determine the equatorial dipole component, d\perp, through a Fourier analysis in R.A. that includes weights for each event so as to account for the main detector-induced systematic effects. For the energies at which the trigger efficiency of the array is small, the "east-west" method is employed. Besides using the data from the array with detectors separated by 1500 m, we also include data from the smaller but denser subarray of detectors with 750 m separation, which allows us to extend the analysis down to ∼0.03 EeV. The most significant equatorial dipole amplitude obtained is that in the cumulative bin above 8 EeV, d\perp={6.0}-0.9+1.0 %, which is inconsistent with isotropy at the 6σ level. In the bins below 8 EeV, we obtain 99% CL upper bounds on d⊥ at the level of 1%-3%. At energies below 1 EeV, even though the amplitudes are not significant, the phases determined in most of the bins are not far from the R.A. of the Galactic center, at αGC = -94°, suggesting a predominantly Galactic origin for anisotropies at these energies. The reconstructed dipole phases in the energy bins above 4 EeV point instead to R.A. that are almost opposite to the Galactic center one, indicative of an extragalactic CR origin.

Keywords: Cosmic ray astronomy, Cosmic ray sources, Cosmic rays