Sazuna/UAT_keywords huggingface dataset:
Bridging the Gap between Cosmic Dawn and Reionization Favors Models Dominated by Faint Galaxies. It has been claimed that traditional models struggle to explain the tentative detection of the 21 cm absorption trough centered at z ~ 17 measured by the EDGES collaboration. On the other hand, it has been shown that the EDGES results are consistent with an extrapolation of a declining UV luminosity density, following a simple power law of deep Hubble Space Telescope observations of 4 &lt; z &lt; 9 galaxies. We here explore the conditions by which the EDGES detection is consistent with current reionization and post-reionization observations, including the neutral hydrogen fraction at z ~ 6-8, Thomson-scattering optical depth, and ionizing emissivity at z ~ 5. By coupling a physically motivated source model derived from radiative transfer hydrodynamic simulations of reionization to a Markov Chain Monte Carlo sampler, we find that it is entirely possible to reconcile existing high-redshift (cosmic dawn) and low-redshift (reionization) constraints. In particular, we find that high contributions from low-mass halos along with high photon escape fractions are required to simultaneously reproduce cosmic dawn and reionization constraints. Our analysis further confirms that low-mass galaxies produce a flatter emissivity evolution, which leads to an earlier onset of reionization with a gradual and longer duration, resulting in a higher optical depth. While the models dominated by faint galaxies successfully reproduce the measured globally averaged quantities over the first one billion years, they underestimate the late redshift-instantaneous measurements in efficiently star-forming and massive systems. We show that our (simple) physically motivated semianalytical prescription produces results that are consistent with the (sophisticated) state-of-the-art THESAN radiation-magnetohydrodynamic simulation of the reionization.

Keywords: Reionization, Galaxies
Massive Black Hole Binaries from the TNG50-3 Simulation. II. Using Dual AGNs to Predict the Rate of Black Hole Mergers. Dual active galaxy nuclei (dAGNs) trace the population of post-merger galaxies and are the precursors to massive black hole (MBH) mergers, an important source of gravitational waves that may be observed by the Laser Interferometer Space Antenna (LISA). In Paper I of this series, we used the population of ≈2000 galaxy mergers predicted by the TNG50-3 simulation to seed semi-analytic models of the orbital evolution and coalescence of MBH pairs with initial separations of ≈1 kpc. Here, we calculate the dAGN luminosities and separations of these pairs as they evolve in post-merger galaxies, and show how the coalescence fraction of dAGNs changes with redshift. We find that because of the several gigayear-long dynamical friction timescale for orbital evolution, the fraction of dAGNs that eventually end in an MBH merger grows with redshift and exceeds 50% beyond z dAGN ≈ 1. Dual AGNs in galaxies with bulge masses ≲1010 M ⊙, or consisting of near-equal-mass MBHs, evolve more quickly and have higher than average coalescence fractions. At any redshift, dAGNs observed with small separations (≲0.7 kpc) have a higher probability of merging before z = 0 than more widely separated systems. Radiation feedback effects can significantly reduce the number of MBH mergers, and this could be manifested as a larger than expected number of widely separated dAGNs. We present a method to estimate the MBH coalescence rate as well as the potential LISA detection rate given a survey of dAGNs. Comparing these rates to the eventual LISA measurements will help determine the efficiency of dynamical friction in post-merger galaxies.

Keywords: Supermassive black holes, Galaxy dynamics, Galaxy nuclei, Galaxy kinematics, Galaxy evolution, Galaxies
A Comparison of Particle-in-cell and Hybrid Simulations of the Heliospheric Termination Shock. We compare hybrid (kinetic proton, fluid electron) and particle-in-cell (kinetic proton, kinetic electron) simulations of the solar wind termination shock with parameters similar to those observed by Voyager 2 during its crossing. The steady-state results show excellent agreement between the downstream variations in the density, plasma velocity, and magnetic field. The quasi-perpendicular shock accelerates interstellar pickup ions to a maximum energy limited by the size of the computational domain, with somewhat higher fluxes and maximal energies observed in the particle-in-cell simulation, likely due to differences in the cross-shock electric field arising from electron kinetic-scale effects. The higher fluxes may help address recent discrepancies noted between observations and large-scale hybrid simulations.

Keywords: Termination shock, Heliosphere
From Halos to Galaxies. VII. The Connections between Stellar Mass Growth History, Quenching History, and Halo Assembly History for Central Galaxies. The assembly of galaxies over cosmic time is tightly connected to the assembly of their host dark matter halos. We investigate the stellar mass growth history and the chemical enrichment history of central galaxies in the Sloan Digital Sky Survey Mapping Nearby Galaxies at Apache Point Observatory. We find that the derived stellar metallicity of passive central galaxies is always higher than that of the star-forming ones. This stellar metallicity enhancement becomes progressively larger toward low-mass galaxies (at a given epoch) and earlier epochs (at a given stellar mass), which suggests strangulation as the primary mechanism for star formation quenching in central galaxies not only in the local Universe but also very likely at higher redshifts up to z ~ 3. We show that at the same present-day stellar mass, passive central galaxies assembled half of their final stellar mass ~2 Gyr earlier than star-forming central galaxies, which agrees well with the semi-analytic model. Exploring the semi-analytic model, we find that this is because passive central galaxies reside in, on average, more massive halos with a higher halo mass increase rate across cosmic time. As a consequence, passive central galaxies are assembled faster and also quenched earlier than their star-forming counterparts. While at the same present-day halo mass, different halo assembly history also produces a very different final stellar mass of the central galaxy within, and halos assembled earlier host more massive centrals with a higher quenched fraction, in particular around the "golden halo mass" at 1012 M ⊙. Our results call attention back to the dark matter halo as a key driver of galaxy evolution.

Keywords: Galaxy dark matter halos, Star formation, Galaxy evolution
On the Parameters of the Spherically Symmetric Parameterized Rezzolla-Zhidenko Spacetime through Solar System Tests, the Orbit of the S2 Star about Sgr A*, and Quasiperiodic Oscillations. In this paper, we find the higher-order expansion parameters α and λ of spherically symmetric parameterized Rezzolla-Zhidenko (PRZ) spacetime by using its functions of the radial coordinate. We subject the parameters of this spacetime to classical tests, including weak gravitational field effects in the solar system, observations of the S2 star that is located in the star cluster close to the Sgr A⋆, and of the frequencies of selected microquasars. Based on this spherically symmetric spacetime, we perform the analytic calculations for solar system effects such as perihelion shift, light deflection, and gravitational time delay to determine limits on the parameters by using observational data. We restrict our attention to the limits on the two higher-order expansion parameters α and λ that survive at the horizon or near the horizon of spherically symmetric metrics. The properties of the expansion of these two small parameters in PRZ parameterization are discussed. We further apply Markov Chain Monte Carlo simulations to analyze and obtain the limits on the expansion parameters by using observations of the phenomena of the S2 star. Finally, we consider the epicyclic motions and derive analytic expressions of the epicyclic frequencies. Applying these expressions to the quasiperiodic oscillations of selected microquasars allows us to set further limits on the parameters of the PRZ spacetime. Our results demonstrate that the higher-order expansion parameters can be given in the range α, λ = (-0.09, 0.09) and of order ~10-2 as a consequence of three different tests and observations.

Keywords: X-ray binary stars, Black holes
Rotational Components of the Sun's Mean Field. This paper uses wavelet transforms to look for the rotational frequencies of the Sun's mean line-of-sight magnetic field. For a sufficiently high wavelet frequency, the spectra of the dipole, quadrupole, and hexapole field components each show a time-dependent fine structure with periods in the range of 26.5-30 days and their harmonics. These maps confirm that a large enhancement of power at 30 days occurred in the dipole field during 1989-1990, as recorded previously using Fourier techniques. In addition, during some years the maps show power at 26.5 days (or its harmonics), which is clearly distinguishable from the rotation period of 26.9-27.0 days at the Sun's equator. In at least one case, the 26.5-day period was a wave phenomenon caused by the systematic eruption of active regions at progressively more western locations in the Carrington coordinate system, as if the flux were emerging from a fixed longitude in a faster-rotating subsurface layer. Based on previous studies of the mean field, I conclude that the enhanced wavelet patterns in this paper are regions where magnetic flux is emerging in configurations that strengthen the Sun's horizontal dipole, quadrupole, and hexapole fields, and (in the case of the more slowly rotating patterns) where this flux is being transported to midlatitudes whose rotation periods are in the range of 28-30 days.

Keywords: Solar cycle, Stellar magnetic fields, Solar rotation, Solar magnetic fields
Branching Fractions and Transition Probabilities for UV Transitions in the Spectrum of Cr II. We present transition probabilities for 268 spectral lines of singly ionized chromium (Cr II) in the wavelength region 208-414 nm. Branching fractions were measured in archival Fourier transform spectra of chromium-argon and chromium-neon hollow cathode lamps and a Penning discharge source. The branching fractions were combined with previously published experimental lifetimes of 14 levels, and with lifetimes from semiempirical calculations for 14 levels to give transition probabilities. The estimated uncertainties of the transition probabilities range from 10% to 26%. A comparison with previously published experimental transition probabilities shows discrepancies of up to a factor of 2.5 for lines around 213 nm.

Keywords: Atomic spectroscopy, Transition probabilities, Atomic data
How to Detect an Astrophysical Nanohertz Gravitational Wave Background. Analyses of pulsar timing data have provided evidence for a stochastic gravitational wave background in the nanohertz frequency band. The most plausible source of this background is the superposition of signals from millions of supermassive black hole binaries. The standard statistical techniques used to search for this background and assess its significance make several simplifying assumptions, namely (i) Gaussianity, (ii) isotropy, and most often, (iii) a power-law spectrum. However, a stochastic background from a finite collection of binaries does not exactly satisfy any of these assumptions. To understand the effect of these assumptions, we test standard analysis techniques on a large collection of realistic simulated data sets. The data-set length, observing schedule, and noise levels were chosen to emulate the NANOGrav 15 yr data set. Simulated signals from millions of binaries drawn from models based on the Illustris cosmological hydrodynamical simulation were added to the data. We find that the standard statistical methods perform remarkably well on these simulated data sets, even though their fundamental assumptions are not strictly met. They are able to achieve a confident detection of the background. However, even for a fixed set of astrophysical parameters, different realizations of the universe result in a large variance in the significance and recovered parameters of the background. We also find that the presence of loud individual binaries can bias the spectral recovery of the background if we do not account for them.

Keywords: Supermassive black holes, Bayesian statistics, Millisecond pulsars, Astronomy data analysis, Gravitational wave sources, Gravitational wave astronomy, Gravitational waves
Switchbacks and Associated Magnetic Holes Observed near the Alfvén Critical Surface. During recent solar encounters, the Parker Solar Probe (PSP) began its initial dips below the Alfvén critical surface to measure in situ the sub-Alfvénic coronal wind. While the near-Sun super-Alfvénic solar wind is shown to be dominated by impulsive magnetic switchbacks (short magnetic field reversals), these brief encounters with the sub-Alfvénic coronal wind show switchbacks and associated magnetic holes (MHs) to still be present but different in character. In this work, we compare and contrast specific features of the switchbacks, including the change in B  r  and V  r  and associated boundary B-field dropouts (MHs) at locations when PSP was both above and below the Alfvén critical surface. We use observations from the PSP perihelion Encounters 8 (E8) and 12 (E12) in the analysis. We first perform a superposed epoch analysis to identify common features in the switchback boundaries, including the formation of the associated ∣B∣ dropouts/MHs in slow and fast flows. We then examine the presence of B-field dropouts/MHs as a function of Alfvén Mach number, M A. From E12, we find that the switchbacks have a systematic reduction in rotation (and reduction in B  r  deflection) with decreasing M A. Further, the ∣B∣ dropouts/MHs associated with the boundaries were also found to decrease in strength and occurrence with M A (with no or few ∣B∣ dropouts at M A &lt; 0.7). The results suggest that the switchback rotation and boundary-associated MHs are connected, possibly consistent with diamagnetic effects at the boundary that require large rotations to be initiated.

Keywords: Solar wind, Solar magnetic fields, Plasma physics
Observational Evidence of a Centi-parsec Supermassive Black Hole Binary Existing in the Nearby Galaxy M81. Studying a centi-parsec supermassive black hole binary (SMBHB) would allow us to explore a new parameter space in active galactic nuclei, and these objects are also potential sources of gravitational waves. We report evidence that an SMBHB with an orbital period of ~30 yr may be resident in the nearby galactic nucleus M81. This orbital period and the known mass of M81 imply an orbital separation of ~0.02 pc. The jet emanating from the primary black hole showed a short period of jet wobbling at ~16.7 yr, superposing a long-term precession at a timescale of several hundred years. Periodic radio and X-ray outbursts were also found two times per orbital period, which could be explained by a double-peaked mass accretion rate variation per binary orbit. If confirmed, M81 would be one of the closest SMBHB candidates, providing a rare opportunity to study the final parsec problem.

Keywords: Supermassive black holes, Very long baseline interferometry
Probing the Low-mass End of Core-collapse Supernovae Using a Sample of Strongly-stripped Calcium-rich Type IIb Supernovae from the Zwicky Transient Facility. The fate of stars in the zero-age main-sequence (ZAMS) range ≈8-12 M ⊙ is unclear. They could evolve to form white dwarfs or explode as electron-capture supernovae (SNe) or iron core-collapse SNe (CCSNe). Even though the initial mass function indicates that this mass range should account for over 40% of all CCSN progenitors, few have been observationally confirmed, likely due to the faintness and rapid evolution of some of these transients. In this paper, we present a sample of nine Ca-rich/O-poor Type IIb SNe detected by the Zwicky Transient Facility with progenitors likely in this mass range. These sources have a [Ca II] λ λ7291, 7324/[O I] λ λ6300, 6364 flux ratio of ≳2 in their nebular spectra. Comparing the measured [O I] luminosity (≲1039 erg s-1) and derived oxygen mass (≈0.01 M ⊙) with theoretical models, we infer that the progenitor ZAMS mass for these explosions is less than 12 M ⊙. The ejecta properties (M ej ≲ 1 M ⊙ and E kin ~ 1050 erg) are also consistent. The low ejecta mass of these sources indicates a class of strongly-stripped SNe that is a transition between the regular stripped-envelope SNe and ultra-stripped SNe. The progenitor could be stripped by a main-sequence companion and result in the formation of a neutron star-main sequence binary. Such binaries have been suggested to be progenitors of neutron star-white dwarf systems that could merge within a Hubble time and be detectable with LISA.

Keywords: Compact binary stars, Supernovae, Core-collapse supernovae
The Jet Opening Angle and Event Rate Distributions of Short Gamma-Ray Bursts from Late-time X-Ray Afterglows. We present a comprehensive study of 29 short gamma-ray bursts (SGRBs) observed ≈0.8-60 days postburst using Chandra and XMM-Newton. We provide the inferred distributions of the SGRB jet opening angles and true event rates to compare against neutron star merger rates. We perform a uniform analysis and modeling of their afterglows, obtaining 10 opening angle measurements and 19 lower limits. We report on two new opening angle measurements (SGRBs 050724A and 200411A) and eight updated values, obtaining a median value of &lt;θ j&gt; ≈ 6.°1 [-3.°2, +9.°3] (68% confidence on the full distribution) from jet measurements alone. For the remaining events, we infer θ j ≳ 0.°5-26°. We uncover a population of SGRBs with wider jets of θ j ≳ 10° (including two measurements of θ j ≳ 15°), representing ~28% of our sample. Coupled with multiwavelength afterglow information, we derive a total true energy of &lt;E true,tot&gt; ≈ 1049-1050 erg, which is consistent with magnetohydrodynamic jet launching mechanisms. Furthermore, we determine a range for the beaming-corrected event rate of ${{\mathfrak{R}}}_{{\rm{true}}}\approx 360-1800$ Gpc-3 yr-1, set by the inclusion of a population of wide jets on the low end, and the jet measurements alone on the high end. From a comparison with the latest merger rates, our results are consistent with the majority of SGRBs originating from binary neutron star mergers. However, our inferred rates are well above the latest neutron star-black hole merger rates, consistent with at most a small fraction of SGRBs originating from such mergers.

Keywords: Gamma-ray bursts, Gamma-ray transient sources, Relativistic jets
A Search for Pulsars around Sgr A* in the First Event Horizon Telescope Data Set. In 2017 the Event Horizon Telescope (EHT) observed the supermassive black hole at the center of the Milky Way, Sagittarius A* (Sgr A*), at a frequency of 228.1 GHz (λ = 1.3 mm). The fundamental physics tests that even a single pulsar orbiting Sgr A* would enable motivate searching for pulsars in EHT data sets. The high observing frequency means that pulsars-which typically exhibit steep emission spectra-are expected to be very faint. However, it also negates pulse scattering, an effect that could hinder pulsar detections in the Galactic center. Additionally, magnetars or a secondary inverse Compton emission could be stronger at millimeter wavelengths than at lower frequencies. We present a search for pulsars close to Sgr A* using the data from the three most sensitive stations in the EHT 2017 campaign: the Atacama Large Millimeter/submillimeter Array, the Large Millimeter Telescope, and the IRAM 30 m Telescope. We apply three detection methods based on Fourier-domain analysis, the fast folding algorithm, and single-pulse searches targeting both pulsars and burst-like transient emission. We use the simultaneity of the observations to confirm potential candidates. No new pulsars or significant bursts were found. Being the first pulsar search ever carried out at such high radio frequencies, we detail our analysis methods and give a detailed estimation of the sensitivity of the search. We conclude that the EHT 2017 observations are only sensitive to a small fraction (≲2.2%) of the pulsars that may exist close to Sgr A*, motivating further searches for fainter pulsars in the region.

Keywords: Neutron stars, Black hole physics, Supermassive black holes, Galactic center, Radio transient sources, Surveys, Millimeter astronomy, Pulsars, Period search , Interstellar scattering, Magnetars, Radio pulsars
Ion Kinetics of Plasma Interchange Reconnection in the Lower Solar Corona. The exploration of the inner heliosphere by the Parker Solar Probe has revealed a highly structured solar wind with ubiquitous deflections from the Parker spiral, known as switchbacks. Interchange reconnection (IR) may play an important role in generating these switchbacks, by forming unstable particle distributions that generate wave activity that in turn may evolve to such structures. IR occurs in very low-beta plasmas and in the presence of strong guiding fields. Although IR is unlikely to release enough energy to provide an important contribution to the heating and acceleration of the solar wind, it affects the way the solar wind is connected to its sources, connecting open field lines to regions of closed fields. This "switching on" provides a mechanism by which the plasma near coronal hole boundaries can mix with that trapped inside the closed loops. This mixing can lead to a new energy balance. It may significantly change the characteristics of the solar wind because this plasma is already preheated and can potentially have quite different density and particle distributions. It not only replenishes the solar wind, but also affects the electric field, which in turn affects the energy balance. This interpenetration is manifested by the formation of a bimodal ion distribution, with a core and a beam-like population. Such distributions are indeed frequently observed by the Parker Solar Probe. Here we provide a first step toward assessing the role of such processes in accelerating and heating the solar wind.

Keywords: Solar corona, Solar coronal heating, Solar wind, Solar magnetic reconnection
Helioseismic Investigation of Quasi-biennial Oscillation Source Regions. We studied the temporal evolution of quasi-biennial oscillations (QBOs) using acoustic mode oscillation frequencies from the Global Oscillation Network Group. The data used here span more than 25 yr, covering solar cycles 23 and 24 and the ascending phase of cycle 25. The analysis reveals that QBO-like signals are present in both the cycles, but with different periods. The dominant QBO period in cycle 23 is found to be about 2 yr, while it is about 3 yr in cycle 24. Furthermore, the quasi-biennial oscillatory signals are present only during the ascending and high-activity phases of cycle 23 and quickly weaken around 2005, during the declining phase. In comparison, the QBO signals are present throughout cycle 24, starting from 2009 to 2017. We also explored the depth dependence in QBO signals and obtained a close agreement at all depths, except in the near-surface shear layer. A detailed analysis of the near-surface shear layer suggests that the source region of QBOs is probably within a few thousand kilometers just below the surface.

Keywords: Solar interior, Helioseismology, Period search , Solar physics, Solar oscillations, Time series analysis