Sazuna/UAT_keywords huggingface dataset:
Wave Emission of Nonthermal Electron Beams Generated by Magnetic Reconnection. Magnetic reconnection in solar flares can efficiently generate nonthermal electron beams. The energetic electrons can, in turn, cause radio waves through microscopic plasma instabilities as they propagate through the ambient plasma along the magnetic field lines. We aim at investigating the wave emission caused by fast-moving electron beams with characteristic nonthermal electron velocity distribution functions (EVDFs) generated by kinetic magnetic reconnection: two-stream EVDFs along the separatrices and in the diffusion region, and perpendicular crescent-shaped EVDFs closer to the diffusion region. For this purpose, we utilized 2.5D fully kinetic Particle-In-Cell code simulations in this study. We found the following: (1) the two-stream EVDFs plus the background ions are unstable to electron/ion (streaming) instabilities, which cause ion-acoustic waves and Langmuir waves due to the net current. This can lead to multiple-harmonic plasma emission in the diffusion region and the separatrices of reconnection. (2) The perpendicular crescent-shaped EVDFs can cause multiple-harmonic electromagnetic electron cyclotron waves through the electron cyclotron maser instabilities in the diffusion region of reconnection. Our results are applicable to diagnose the plasma parameters, which are associated to magnetic reconnection in solar flares by means of radio wave observations.

Keywords: Solar radio emission, Non-thermal radiation sources, Astronomical radiation sources, Solar electromagnetic emission
Growth of Outward Propagating Fast-magnetosonic/Whistler Waves in the Inner Heliosphere Observed by Parker Solar Probe. The solar wind in the inner heliosphere has been observed by Parker Solar Probe (PSP) to exhibit abundant wave activities. The cyclotron wave modes responding to ions or electrons are among the most crucial wave components. However, their origin and evolution in the inner heliosphere close to the Sun remains a mystery. Specifically, it remains unknown whether it is an emitted signal from the solar atmosphere or an eigenmode growing locally in the heliosphere due to plasma instability. To address and resolve this controversy, we must investigate the key quantity of the energy change rate of the wave mode. We develop a new technique to measure the energy change rate of plasma waves, and apply this technique to the wave electromagnetic fields measured by PSP. We provide the wave Poynting flux in the solar wind frame, identify the wave nature to be the outward propagating fast-magnetosonic/whistler wave mode instead of the sunward propagating waves. We provide the first evidence for growth of the fast-magnetosonic/whistler wave mode in the inner heliosphere based on the derived spectra of the real and imaginary parts of the wave frequencies. The energy change rate rises and stays at a positive level in the same wavenumber range as the bumps of the electromagnetic field power spectral densities, clearly manifesting that the observed fast-magnetosonic/whistler waves are locally growing to a large amplitude.

Keywords: Interplanetary turbulence, Solar wind
Flat-spectrum Radio Quasars and BL Lacs Dominate the Anisotropy of the Unresolved Gamma-Ray Background. We analyze the angular power spectrum (APS) of the unresolved gamma-ray background (UGRB) emission and combine it with the measured properties of the resolved gamma-ray sources of the Fermi-LAT 4FGL catalog. Our goals are to dissect the composition of the gamma-ray sky and to establish the relevance of different classes of source populations of active galactic nuclei in determining the observed size of the UGRB anisotropy, especially at low energies. We find that, under physical assumptions for the spectral energy distribution, i.e., by using the 4FGL catalog data as a prior, two populations are required to fit the APS data, namely flat-spectrum radio quasars at low energies and BL Lacs at higher energies. The inferred luminosity functions agree well with the extrapolation of the flat-spectrum radio quasar and BL Lac ones obtained from the 4FLG catalog. We use these luminosity functions to calculate the UGRB intensity from blazars, finding a contribution of 20% at 1 GeV and 30% above 10 GeV. Finally, bounds on an additional gamma-ray emission due to annihilating dark matter are also derived.

Keywords: Gamma-ray sources, Blazars, Gamma-rays
CLASSY III. The Properties of Starburst-driven Warm Ionized Outflows. We report the results of analyses of galactic outflows in a sample of 45 low-redshift starburst galaxies in the COS Legacy Archive Spectroscopic SurveY (CLASSY), augmented by five additional similar starbursts with Cosmic Origins Spectrograph (COS) data. The outflows are traced by blueshifted absorption lines of metals spanning a wide range of ionization potential. The high quality and broad spectral coverage of CLASSY data enable us to disentangle the absorption due to the static interstellar medium (ISM) from that due to outflows. We further use different line multiplets and doublets to determine the covering fraction, column density, and ionization state as a function of velocity for each outflow. We measure the outflow's mean velocity and velocity width, and find that both correlate in a highly significant way with the star formation rate, galaxy mass, and circular velocity over ranges of four orders of magnitude for the first two properties. We also estimate outflow rates of metals, mass, momentum, and kinetic energy. We find that, at most, only about 20% of silicon created and ejected by supernovae in the starburst is carried out in the warm phase we observe. The outflows' mass-loading factor increases steeply and inversely with both circular and outflow velocity (log-log slope ~-1.6), and reaches ~10 for dwarf galaxies. We find that the outflows typically carry about 10%-100% of the momentum injected by massive stars and about 1%-20% of the kinetic energy. We show that these results place interesting constraints on, and new insights into, models and simulations of galactic winds. *Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Keywords: Starburst galaxies, Galactic winds, Galaxy dynamics, Ultraviolet astronomy, Galaxy kinematics, Galaxy evolution, Galaxy spectroscopy
Probing the Extragalactic Mid-infrared Background with HAWC. The extragalactic background light (EBL) contains all the radiation emitted by nuclear and accretion processes in stars and compact objects since the epoch of recombination. Measuring the EBL density directly is challenging, especially in the near-to-far-infrared wave band, mainly due to the zodiacal light foreground. Instead, gamma-ray astronomy offers the possibility to indirectly set limits on the EBL by studying the effects of gamma-ray absorption in the very high energy (VHE: &gt;100 GeV) spectra of distant blazars. The High Altitude Water Cherenkov Gamma Ray Observatory (HAWC) is one of the few instruments sensitive to gamma rays with energies above 10 TeV. This offers the opportunity to probe the EBL in the near/mid-IR region: λ = 1-100 μm. In this study, we fit physically motivated emission models to Fermi-LAT gigaelectronvolt data to extrapolate the intrinsic teraelectronvolt spectra of blazars. We then simulate a large number of absorbed spectra for different randomly generated EBL model shapes and calculate Bayesian credible bands in the EBL intensity space by comparing and testing the agreement between the absorbed spectra and HAWC extragalactic observations of two blazars. The resulting bands are in agreement with current EBL lower and upper limits, showing a downward trend toward higher wavelength values λ &gt; 10 μm also observed in previous measurements.

Keywords: Diffuse radiation, Gamma-ray astronomy, Blazars
Multiwavelength Variation Phenomena of PKS 0735+178 on Diverse Timescales. The BL Lac object PKS 0735+178 has shown some complex multiwavelength variation phenomena in previous studies, especially in its color behavior. Bluer-when-brighter, redder-when-brighter, and achromatic behavior were all found to be possible long-term trends of PKS 0735+178. In this work, we collected long-term multiwavelength data on PKS 0735+178, and also performed a multicolor optical monitoring on intraday timescales. Intraday variability was detected on one night. On long timescales, a possible 22 day time lag was found between the R and γ-ray bands. The results of a cross-correlation analysis exhibited strong correlations between various optical bands on both intraday and long timescales. However, only a mild correlation was found between the long-term γ-ray and R-band light curves, which could be interpreted as different emission mechanisms for the γ-ray and optical emissions. PKS 0735+178 showed a significant harder-when-brighter (HWB) behavior in the γ-ray band, which is consistent with the observed optical bluer-when-brighter (BWB) trend on both long-term and intraday timescales. We found that the HWB and BWB trends will be enhanced during active states, especially for the historical low state. Such a phenomenon indicates a special activity-dependent color behavior of PKS 0735+178, and it could be well interpreted by the jet emission model.

Keywords: Active galaxies, BL Lacertae objects, Galaxy photometry
A Model for the Possible Connection Between a Tidal Disruption Event and Quasi-periodic Eruption in GSN 069. Quasi-periodic eruptions (QPEs) are found in the center of five galaxies, where a tidal disruption event (TDE)-like event has been reported in GSN 069, which occurred a couple of years before the QPEs. We explain the connection of these phenomena based on a model of a highly eccentric white dwarf (WD) 104-6 M ⊙ massive black hole (MBH) binary formed by the Hill mechanism. In this system, the tidally induced internal oscillation of a WD can heat the WD envelope thereby inducing tidal nova and inflating the WD envelope, which can be captured by the MBH and form a TDE. The tidal stripping of the surviving WD in the eccentric orbit can produce QPEs. We also apply this model to the other four QPE sources. Based on the estimated fallback rate, we find that the remaining time after the QPE-observed time for these QPEs is only around 1-2 yr based on our simple model estimation, after which the WD will be fully disrupted. We also show that the accretion rate can be much higher than the Eddington accretion rate in the final stage of these QPE sources. The peak frequency of the spectral energy distribution of the disk stays in the soft X-ray band (~0.1-1 keV), which is consistent with observational results.

Keywords: Accretion, Black hole physics, White dwarf stars, Tidal disruption, Gravitational wave sources
General Relativistic Implicit Monte Carlo Radiation-hydrodynamics. We report on a new capability added to our general relativistic radiation-magnetohydrodynamics code, Cosmos++: an implicit Monte Carlo (IMC) treatment for radiation transport. The method is based on a Fleck-type implicit discretization of the radiation-hydrodynamics equations, but generalized for both Newtonian and relativistic regimes. A multiple reference frame approach is used to geodesically transport photon packets (and solve the hydrodynamics equations) in the coordinate frame, while radiation-matter interactions are handled either in the fluid or electron frames then communicated via Lorentz boosts and orthonormal tetrad bases attached to the fluid. We describe a method for constructing estimators of radiation moments using path-weighting that generalizes to arbitrary coordinate systems in flat or curved spacetime. Absorption, emission, scattering, and relativistic Comptonization are among the matter interactions considered in this report. We discuss our formulations and numerical methods, and validate our models against a suite of radiation and coupled radiation-hydrodynamics test problems in both flat and curved spacetimes.

Keywords: Radiative magnetohydrodynamics, Hydrodynamics, Relativity, Radiative transfer equation, General relativity, Radiative transfer, Astrophysical fluid dynamics, Geodesics
The BANANA Project. VI. Close Double Stars are Well Aligned with Noticeable Exceptions; Results from an Ensemble Study Using Apsidal Motion and Rossiter-McLaughlin Measurements. Here we present an ensemble study of spin-orbit alignment in 43 close double star systems. We determine spin-orbit angles, obliquities, in 31 of these systems making use of recently improved apsidal motion rate measurements and apsidal motion constants. In the remaining 12 systems researchers have constrained spin-orbit alignment by different combinations of measurements of apsidal motion rates, projected obliquities, and stellar inclinations. Of the 43 systems 40 are consistent with alignment albeit with some measurements having large uncertainties. A Fisher distribution with mean zero and a concentration factor κ = 6.1 represents this ensemble well. Indeed employing a bootstrapping resampling technique we find our data on these 40 systems are consistent with perfect alignment. We also confirm significant misalignment in two systems that travel on eccentric orbits and where misalignments have been reported on before; namely DI Her and AS Cam. The third misaligned system CV Vel orbits on a circular orbit. So while there are some glaring exceptions, the majority of close double star systems for which data are available appear to be well aligned.

Keywords: Oblique rotators, Apsidal motion, Binary stars, Close binary stars, Eclipsing binary stars
The Size-Mass Relation of Post-starburst Galaxies in the Local Universe. We present a study of the size-mass relation for local post-starburst (PSB) galaxies at z ≲ 0.33 selected from the Sloan Digital Sky Survey Data Release 8. We find that PSB galaxies with stellar mass (M *) at 109 M ☉ &lt; M * &lt; 1012 M ☉ have a galaxy size smaller than or comparable to those of quiescent galaxies (QGs). After controlling redshift and stellar mass, the sizes of PSBs are ~13% smaller on average than those of QGs; such differences become larger and significant toward the low-M * end, especially at 109.5 M ☉ ≲ M * ≲ 1010.5 M ☉ where PSBs can be on average ~19% smaller than QGs. By comparing predictions of possible PSB evolutionary pathways from cosmological simulations, we suggest that a fast quenching of star formation following a short-lived starburst event (which might be induced by a major merger) should be the dominant pathway of our PSB sample. Furthermore, by cross-matching with group catalogs, we confirm that local PSBs at M * ≲ 1010 M ☉ are more clustered than more massive ones. PSBs residing in groups are found to be slightly larger in galaxy size and more disk-like compared to field PSBs, which is qualitatively consistent with and thus hints at the environment-driven fast quenching pathway for group PSBs. Taken together, our results support multiple evolutionary pathways for local PSB galaxies: while massive PSBs are thought of as products of fast quenching following a major merger-induced starburst, environment-induced fast quenching should play a role in the evolution of less massive PSBs, especially at M * ≲ 1010 M ☉.

Keywords: Galaxy quenching, Galaxy structure, Galaxy evolution, Post-starburst galaxies
Discovery of a Cool, Metal-rich Gas Reservoir in the Outskirts of z ≈ 0.5 Clusters. We built the first-ever statistically significant sample of ≈80,000 background quasar-foreground cluster pairs to study the cool, metal-rich gas in the outskirts (&gt;R 500) of z ≈ 0.5 clusters with a median mass of ≈1014.2 M ⊙. The sample was obtained by crossmatching the Sloan Digital Sky Survey (SDSS) cluster catalog of Wen &amp; Han and the SDSS quasar catalog of Lyke et al. The median impact parameter (ρ cl) of the clusters from the quasar sightlines is 2.4 Mpc (median ρ cl/R 500 = 3.6). A strong Mg II, along with marginal Fe II, absorption is detected in the mean and median stacked spectra of the quasars with a total Mg II rest-frame equivalent width ( ${W}_{r}^{2796+2803}$ ) of 0.034 ± 0.005 Å (7σ) and 0.010 ± 0.003 Å (3σ), respectively. The ${W}_{r}^{2796+2803}$ shows a declining trend with increasing ρ cl and ρ cl/R 500, but does not show any significant trend with mass (M 500) or redshift (z cl) within the small M 500 and z cl ranges probed here. The Mg II absorption signal and the trends persist even if we exclude the quasar-cluster pairs where the background quasars may be probing the circumgalactic medium of bright galaxies with impact parameters &lt;300 kpc. The Mg II (and Fe II) absorption reported here is the first detection of its kind. It indicates the presence of a cool, metal-rich gas reservoir surrounding galaxy clusters out to several R 500. We suggest that the metal-rich gas in the cluster outskirts arise from stripped materials and that gas stripping may be important out to large clustocentric distances (&gt;3R 500).

Keywords: Galaxy clusters, Quasar absorption line spectroscopy, Intergalactic medium, Extragalactic astronomy, Intracluster medium, Galaxies
Vertical Distribution of Cyclopropenylidene and Propadiene in the Atmosphere of Titan. Titan's atmosphere is a natural laboratory for exploring the photochemical synthesis of organic molecules. Significant recent advances in the study of the atmosphere of Titan include: (a) detection of C3 molecules: C3H6, CH2CCH2, c-C3H2, and (b) retrieval of C6H6, which is formed primarily via C3 chemistry, from Cassini Ultraviolet Imaging Spectrograph data. The detection of c-C3H2 is of particular significance as ring molecules are of great astrobiological importance. Using the Caltech/JPL KINETICS code, along with the best available photochemical rate coefficients and parameterized vertical transport, we are able to account for the recent observations. It is significant that ion chemistry, reminiscent of that in the interstellar medium, plays a major role in the production of c-C3H2 above 1000 km.

Keywords: Atmospheric composition, Planetary atmospheres, Titan
Radio Emission of Pulsars. I. Slow Tearing of a Quantizing Magnetic Field. The pulsed radio emission of rotating neutron stars is connected to slow tearing instabilities feeding off an inhomogeneous twist profile within the open circuit. This paper considers the stability of a weakly sheared, quantizing magnetic field in which the current is supported by a relativistic particle flow. The electromagnetic field is almost perfectly force free, and particles are confined to the lowest Landau state, experiencing no appreciable curvature drift. In a charge-neutral plasma, we find multiple branches of slowly growing tearing modes, relativistic analogs of the double-tearing mode, with peak growth rate $s\gtrsim 4\pi {\widetilde{k}}_{y}{J}_{z}/{B}_{z}$ . Here, B  z  is the strong (nearly potential) guide magnetic field, J  z  the field-aligned current density, and ${\widetilde{k}}_{y}$ is the mode wavenumber normalized by the current gradient scale. These modes are overstable when the plasma carries a net charge, with the real frequency $\omega \sim s\cdot | {n}_{0}^{+}-{n}_{0}^{-}| /({n}_{0}^{+}+{n}_{0}^{-})$ proportional to the imbalance in the densities of positive and negative charges. An isolated current sheet thinner than the skin depth supports localized tearing modes with growth rate scaling as (sheet thickness/skin depth)-1/2. In a pulsar, the peak growth rate is comparable to the angular frequency of rotation, $s\gtrsim 2{\widetilde{k}}_{y}{\rm{\Omega }}$ , slow compared with the longitudinal oscillations of particles and fields in a polar gap. The tearing modes experience azimuthal drift reminiscent of subpulse drift and are a promising driver of pulse-to-pulse flux variations. A companion paper demonstrates a Cerenkov-like instability of current-carrying Alfvén waves in thin current sheets with relativistic particle flow and proposes coherent curvature emission by these waves as a source of pulsar radio emission.

Keywords: Compact radiation sources, Plasma physics, Magnetars, Magnetic fields, Radio pulsars
Radio Emission of Pulsars. II. Coherence Catalyzed by Cerenkov-unstable Shear Alfvén Waves. This paper explores small-scale departures from force-free electrodynamics around a rotating neutron star, extending our treatment of resistive instability in a quantizing magnetic field. A secondary, Cerenkov instability is identified: relativistic particles flowing through thin current sheets excite propagating charge perturbations that are localized near the sheets. Growth is rapid at wavenumbers below the inverse ambient skin depth k  p,ex. Small-scale Alfvénic wavepackets are promising sources of coherent curvature radiation. When the group Lorentz factor ${\gamma }_{\mathrm{gr}}\lesssim {({k}_{p,\mathrm{ex}}{R}_{c})}^{1/3}\sim 100$ , where R  c  is the magnetic curvature radius, a fraction ~10-3-10-2 of the particle kinetic energy is radiated into the extraordinary mode at a peak frequency ~10-2 ck  p,ex. Consistency with observations requires a high pair multiplicity (~103-5) in the pulsar magnetosphere. Neither the primary, slow resistive instability nor the secondary, Alfvénic instability depend directly on the presence of magnetospheric gaps, and may activate where the mean current is fully supplied by outward drift of the corotation charge. The resistive mode is overstable and grows at a rate comparable to the stellar spin frequency; the model directly accommodates strong pulse-to-pulse radio flux variations and coordinated subpulse drift. Alfvén mode growth can track the local plasma conditions, allowing for lower-frequency emission from the outer magnetosphere. Beamed radio emission from charged packets with γ gr ~ 50-100 also varies on submillisecond timescales. The modes identified here will be excited inside the magnetosphere of a magnetar, and may mediate Taylor relaxation of the magnetic twist.

Keywords: Compact radiation sources, Plasma physics, Magnetars, Magnetic fields, Radio pulsars
Large-scale Hydrodynamical Shocks as the Smoking-gun Evidence for a Bar in M31. The formation and evolutionary history of M31 are closely related to its dynamical structures, which remain unclear due to its high inclination. Gas kinematics could provide crucial evidence for the existence of a rotating bar in M31. Using the position-velocity diagram of [O III] and H I, we are able to identify clear sharp velocity jump (shock) features with a typical amplitude over 100 km s-1 in the central region of M31 (4.6 kpc × 2.3 kpc, or $20^{\prime} \times 10^{\prime} $ ). We also simulate gas morphology and kinematics in barred M31 potentials and find that the bar-induced shocks can produce velocity jumps similar to those in [O III]. The identified shock features in both [O III] and H I are broadly consistent, and they are found mainly on the leading sides of the bar/bulge, following a hallmark pattern expected from the bar-driven gas inflow. Shock features on the far side of the disk are clearer than those on the near side, possibly due to limited data coverage on the near side, as well as to obscuration by the warped gas and dust layers. Further hydrodynamical simulations with more sophisticated physics are desired to fully understand the observed gas features and to better constrain the parameters of the bar in M31.

Keywords: Galaxy formation, Interstellar medium, Andromeda Galaxy, Hydrodynamics