Sazuna/UAT_keywords huggingface dataset:
Understanding Broad Mg II Variability in Quasars with Photoionization: Implications for Reverberation Mapping and Changing-look Quasars. The broad Mg II line in quasars has distinct variability properties compared with broad Balmer lines: it is less variable and usually does not display a “breathing” mode, the increase in the average cloud distance when luminosity increases. We demonstrate that these variability properties of Mg II can be reasonably well explained by simple locally optimally emitting cloud (LOC) photoionization models, confirming earlier photoionization results. In the fiducial LOC model, the Mg II-emitting gas is on average more distant from the ionizing source than the Hα/Hβ gas and responds with a lower amplitude to continuum variations. If the broad-line region (BLR) is truncated at a physical radius of ∼0.3 pc (for a 108.5 M ⊙ BH accreting at Eddington ratio of 0.1), most of the Mg II flux will always be emitted near this outer boundary and hence will not display breathing. These results indicate that reverberation mapping results on broad Mg II, while generally more difficult to obtain owing to the lower line responsivity, can still be used to infer the Mg II BLR size and hence black hole mass. But it is possible that Mg II does not have a well-defined intrinsic BLR size-luminosity relation for individual quasars, even though a global one for the general population may still exist. The dramatic changes in broad Hα/Hβ emission in the observationally rare changing-look quasars are fully consistent with photoionization responses to extreme continuum variability, and the LOC model provides natural explanations for the persistence of broad Mg II in changing-look quasars defined on Hα/Hβ and the rare population of broad Mg II emitters in the spectra of massive inactive galaxies.

Keywords: Black hole physics, Reverberation mapping, Active galactic nuclei, Quasars
Effects of Magnetic Field Loops on the Dynamics of Advective Accretion Flows and Jets around a Schwarzschild Black Hole. Magnetic fields advected along with low angular momentum accretion flows predominantly become toroidal owing to the strong azimuthal velocity close to a black hole. We study self-consistently the movements of these flux tubes inside an advective disk and how they dynamically influence the flow. We find that the centrifugal barrier slows down the radial motion of the flux tubes. In this case, the large magnetic flux tubes with a significant drag force escape along the vertical axis owing to buoyancy. Magnetic pressure rises close to the black hole and, together with the centrifugal force, combats gravity. The tug-of-war among these forces causes the centrifugal-pressure-supported shock to oscillate radially. We study the effects of successive injection of flux tubes and find how the flux tube could be trapped inside the disk in regions of highest entropy. Most interestingly, the shock wave remains at its average location and is not destroyed. We show that the toroidal field loops contribute significantly to collimate and accelerate the outflows from the centrifugal barrier and suggest that this mechanism is a way to collimate and accelerate jets.

Keywords: Accretion, Nonrotating black holes, Shocks, Magnetohydrodynamical simulations
Tilting Ice Giants with a Spin-Orbit Resonance. Giant collisions can account for Uranus’s and Neptune’s large obliquities, yet generating two planets with widely different tilts and strikingly similar spin rates is a low-probability event. Trapping into a secular spin-orbit resonance, a coupling between spin and orbit precession frequencies, is a promising alternative, as it can tilt the planet without altering its spin period. We show with numerical integrations that if Uranus harbored a massive circumplanetary disk at least three times the mass of its satellite system while it was accreting its gaseous atmosphere, then its spin precession rate would increase enough to resonate with its own orbit, potentially driving the planet’s obliquity to 70°. We find that the presence of a massive disk moves the Laplace radius significantly outward from its classical value, resulting in more of the disk contributing to the planet’s pole precession. Although we can generate tilts greater than 70° only rarely and cannot drive tilts beyond 90°, a subsequent collision with an object about 0.5 M ⊕ could tilt Uranus from 70° to 98°. Minimizing the masses and number of giant impactors from two or more to just one increases the likelihood of producing Uranus’s spin states by about an order of magnitude. Neptune, by contrast, needs a less massive disk to explain its 30° tilt, eliminating the need for giant collisions altogether.

Keywords: Astrodynamics, Neptune, Solar system planets, Orbits, Orbital resonances, Solar system gas giant planets, Celestial mechanics, N-body simulations, Planet formation, Uranus
The 1.28 GHz MeerKAT DEEP2 Image. We present the confusion-limited 1.28 GHz MeerKAT DEEP2 image covering one {θ }{{b}}≈ 68\prime {FWHM} primary-beam area with θ = 7.″6 FWHM resolution and {σ }n=0.55+/- 0.01 μ {Jy} {beam}}-1 rms noise. Its J2000 center position α = 04h 13m 26.ˢ4, δ = -80° 00‧ 00″ was selected to minimize artifacts caused by bright sources. We introduce the new 64-element MeerKAT array and describe commissioning observations to measure the primary-beam attenuation pattern, estimate telescope pointing errors, and pinpoint (u, V) coordinate errors caused by offsets in frequency or time. We constructed a 1.4 GHz differential source count by combining a power-law count fit to the DEEP2 confusion P(D) distribution from 0.25 to 10 μJy with counts of individual DEEP2 sources between 10 μJy and 2.5 mJy. Most sources fainter than S ∼ 100 μJy are distant star-forming galaxies (SFGs) obeying the far-IR/radio correlation, and sources stronger than 0.25 μJy account for ∼93% of the radio background produced by SFGs. For the first time, the DEEP2 source count has reached the depth needed to reveal the majority of the star formation history of the universe. A pure luminosity evolution of the 1.4 GHz local luminosity function consistent with the Madau &amp; Dickinson model for the evolution of SFGs based on UV and infrared data underpredicts our 1.4 GHz source count in the range -5≲ {log}[S({Jy})]≲ -4.

Keywords: Radio telescopes, Star formation, Galaxy counts
Model-independent Reconstruction of f(T) Gravity from Gaussian Processes. We apply Gaussian processes and Hubble function data in f(T) cosmology to reconstruct for the first time the f(T) form in a model-independent way. In particular, using H(z) data sets coming from cosmic chronometers as well as from the method of radial baryon acoustic oscillations, alongside the latest released local value of H 0 = 73.52 ± 1.62 km s-1 Mpc-1, we reconstruct H(z) and its derivatives, resulting eventually in a reconstructed region for f(T), without any assumption. Although the cosmological constant lies in the central part of the reconstructed region, the obtained mean curve follows a quadratic function. Inspired by this we propose a new f(T) parameterization, I.e., f(T) = -2Λ + ξT 2, with ξ the sole free parameter that quantifies the deviation from ΛCDM cosmology. Additionally, we confront three viable one-parameter f(T) models from the literature, which are the power-law, the square-root exponential, and the exponential models, with the reconstructed f(T) region, and then we extract significantly improved constraints for their model parameters, comparing to the constraints that arise from the usual observational analysis. Finally, we argue that since we are using the direct Hubble measurements and the local value for H 0 in our analysis, the H 0 tension can be efficiently alleviated with the above reconstruction of f(T).

Keywords: Cosmology, Gaussian Processes regression
Gravity-darkening Analysis of the Misaligned Hot Jupiter MASCARA-4 b. MASCARA-4 b is a hot Jupiter in a highly misaligned orbit around a rapidly rotating A3V star that was observed for 54 days by the Transiting Exoplanet Survey Satellite (TESS). We perform two analyses of MASCARA-4 b using a stellar gravity-darkened model. First, we measure MASCARA-4 b’s misaligned orbital configuration by modeling its TESS photometric light curve. We take advantage of the asymmetry in MASCARA-4 b’s transit due to its host star’s gravity-darkened surface to measure MASCARA-4 b’s true spin-orbit angle to be 104°{}-{13^\circ }+{7^\circ }. We also detect a ∼4σ secondary eclipse at 0.491 ± 0.007 orbital phase, proving that the orbit is slightly eccentric. Second, we model MASCARA-4 b’s insolation including gravity darkening and find that the planet’s received X-ray and ultraviolet flux varies by 4% throughout its orbit. MASCARA-4 b’s short-period, polar orbit suggests that the planet likely underwent dramatic orbital evolution to end up in its present-day configuration and that it receives a varying stellar irradiance that perpetually forces the planet out of thermal equilibrium. These findings make MASCARA-4 b an excellent target for follow-up characterization to better understand the orbital evolution and present-day environment of planets around high-mass stars.

Keywords: Inclination, Exoplanets, Hot Jupiters, Planetary alignment, Exoplanet systems, Exoplanet astronomy, von Zeipel theorem, Stellar rotation, Extrasolar gaseous giant planets, Gravity darkening
Viscous Evolution of Magnetized Clumps: A Source for X-Ray Flares in Gamma-Ray Bursts. X-ray flares may indicate the late-time activity of the central engines of gamma-ray bursts. Such long-term activity has been described through some models, one of which is the viscous evolution of the outer disk’s fragments proposed by Perna et al., and developed quantitatively by Dall’Osso et al. Here, we reconstruct the framework of Dall’Osso et al. by taking both small- and large-scale effects of magnetic field into account. To consider the magnetic barrier as a possible mechanism that might govern the accretion process of each magnetized clump, we construct a simple pattern in boundary conditions through which this mechanism might act. Regarding various model parameters, we probe for their influence and follow some key analogies between our model predictions and previous phenomenological estimates, for two different choices of boundary conditions (with and without a magnetic barrier). Our model is remarkably capable of matching the bolometric and X-ray light curves of flares, as well as reproducing their statistical properties, such as the ratios between rise and decay time, width parameter and peak time, and the power-law correlation between peak luminosity and peak time. Combining our results with the conclusions of previous studies, we are led to interpret a magnetic barrier as a less probable mechanism that might control the evolution of these clumps, especially those created later (or viscously evolved ones).

Keywords: Accretion, Gamma-ray bursts, Magnetic fields
A New Channel of Bulge Formation via the Destruction of Short Bars. Short (inner) bars of subkiloparsec radius have been hypothesized to be an important mechanism for driving gas inflows to small scales, thus feeding central black holes (BHs). Recent numerical simulations have shown that the growth of central BHs in galaxies can destroy short bars, when the BH reaches a mass of ∼0.1% of the total stellar mass of the galaxy. We study N-body simulations of galaxies with single and double bars to track the long-term evolution of the central stellar mass distribution. We find that the destruction of the short bar contributes significantly to the growth of the bulge. The final bulge mass is roughly equal to the sum of the masses of the initial pseudo bulge and short bar. The initially boxy/peanut-shaped bulge of Sérsic index n ≲ 1 is transformed into a more massive, compact structure that bears many similarities to a classical bulge, in terms of its morphology (n ≈ 2), kinematics (dispersion-dominated, isotropic), and location on standard scaling relations (Kormendy relation, mass-size relation, and correlations between BH mass and bulge stellar mass and velocity dispersion). Our proposed channel for forming classical bulges relies solely on the destruction of short bars without any reliance on mergers. We suggest that some of the less massive, less compact classical bulges were formed in this manner.

Keywords: Black hole physics, Galaxy structure, Galaxy physics, Galaxy dynamics, Galaxy bulges, Milky Way evolution
SOFIA/HAWC+ Traces the Magnetic Fields in NGC 1068. We report the first detection of galactic spiral structure by means of thermal emission from magnetically aligned dust grains. Our 89 μm polarimetric imaging of NGC 1068 with the High-resolution Airborne Wideband Camera/Polarimeter (HAWC+) on NASAs Stratospheric Observatory for Infrared Astronomy (SOFIA) also sheds light on magnetic field structure in the vicinity of the galaxy's inner-bar and active galactic nucleus (AGN). We find correlations between the 89 μm magnetic field vectors and other tracers of spiral arms, and a symmetric polarization pattern as a function of the azimuthal angle arising from the projection and inclination of the disk field component in the plane of the sky. The observations can be fit with a logarithmic spiral model with pitch angle of {16.9}-2.8+2.7\circ and a disk inclination of 48° ± 2°. We infer that the bulk of the interstellar medium from which the polarized dust emission originates is threaded by a magnetic field that closely follows the spiral arms. Inside the central starburst disk (&lt;1.6 kpc), the degree of polarization is found to be lower than for far-infrared sources in the Milky Way, and has minima at the locations of most intense star formation near the outer ends of the inner-bar. Inside the starburst ring, the field direction deviates from the model, becoming more radial along the leading edges of the inner-bar. The polarized flux and dust temperature peak ∼3″-6″ NE of the AGN at the location of a bow shock between the AGN outflow and the surrounding interstellar medium, but the AGN itself is weakly polarized (&lt;1%) at both 53 and 89 μm.

Keywords: Spiral galaxies, Far infrared astronomy, Active galactic nuclei, Spiral pitch angle, Polarimetry
Constraining the Observer Angle of the Kilonova AT2017gfo Associated with GW170817: Implications for the Hubble Constant. There is a strong degeneracy between the luminosity distance (D  L ) and the observer viewing angle (θ obs; hereafter viewing angle) of the gravitational wave (GW) source with an electromagnetic counterpart, GW170817. Here, for the first time, we present independent constraints on {θ }obs}={32.5}-9.7^\circ +11.7 from broadband photometry of the kilonova (kN) AT2017gfo associated with GW170817. These constraints are consistent with independent results presented in the literature using the associated gamma-ray burst GRB 170817A. Combining the constraints on θ obs with the GW data, we find an improvement of 24% on H 0. The observer angle constraints are insensitive to other model parameters, e.g., the ejecta mass, the half-opening angle of the lanthanide-rich region and the temperature. A broad wavelength coverage extending to the near-infrared is helpful to robustly constrain θ obs. While the improvement on H 0 presented here is smaller than the one from high angular resolution imaging of the radio counterpart of GW170817, kN observations are significantly more feasible at the typical distances of such events from current and future LIGO-Virgo collaboration observing runs (D  L  ∼ 100 Mpc). Our results are insensitive to the assumption of the peculiar velocity of the kN host galaxy.

Keywords: Hubble constant, Gravitational waves, Radiative transfer, Cosmological parameters
Propagation of Alfvén Waves in the Expanding Solar Wind with the Fast-Slow Stream Interaction. We carry out two-dimensional magnetohydrodynamic simulations of an ensemble of Alfvénic fluctuations propagating in a structured, expanding solar wind including the presence of fast and slow solar wind streams. Using an appropriate expanding box model, the simulations incorporate the effects of fast-slow stream shear and compression and rarefaction self-consistently. We investigate the radial and longitudinal evolution of the cross helicity, the total and residual energies and the power spectra of outward and inward Alfvénic fluctuations. The stream interaction is found to strongly affect the radial evolution of Alfvénic turbulence. The total energy in the Alfvén waves is depleted within the velocity shear regions, accompanied by the decrease of the normalized cross helicity. The presence of stream compression facilitates this process. Residual energy fluctuates around zero due to the correlation and de-correlation between the inward/outward waves but no net growth or decrease of the residual energy is observed. The radial power spectra of the inward/outward Alfvén waves show significant longitudinal variations. Kolmogorov-like spectra are developed only inside the fast and slow streams and when both the compression and shear are present. On the other hand, the spectra along the longitudinal direction show clear Kolmogorov-like inertial ranges in all cases.

Keywords: Interplanetary turbulence, Solar wind, Alfven waves, Corotating streams
Analytic Model for the Time-dependent Electromagnetic Field of an Astrophysical Jet. An analytic model of the time-dependent electric and magnetic fields of an astrophysical jet is presented. These fields satisfy the time-dependent Faraday’s law and describe a jet with increasing length. The electric field contains both electrostatic and inductive parts. The electrostatic part corresponds to the rate of injection of toroidal magnetic flux, while the sum of the electrostatic and inductive parts results in the electric field parallel to the magnetic field being zero everywhere. The pinch force associated with the electric current provides a peaked pressure on the jet axis and a pressure minimum at the radius where the poloidal magnetic field reverses direction.

Keywords: Accretion, Magnetohydrodynamics, Jets, Stellar jets, Young stellar objects, Stellar accretion disks, Collimation
Mitigating Internal Instrument Coupling for 21 cm Cosmology. II. A Method Demonstration with the Hydrogen Epoch of Reionization Array. We present a study of internal reflection and cross-coupling systematics in Phase I of the Hydrogen Epoch of Reionization Array (HERA). In a companion paper, we outlined the mathematical formalism for such systematics and presented algorithms for modeling and removing them from the data. In this work, we apply these techniques to data from HERA’s first observing season as a method demonstration. The data show evidence for systematics that, without removal, would hinder a detection of the 21 cm power spectrum for the targeted Epoch of Reionization (EoR) line-of-sight modes in the range 0.2 h -1 Mpc-1 &lt; {k}\parallel  &lt; 0.5 h -1 Mpc-1. In particular, we find evidence for nonnegligible amounts of spectral structure in the raw autocorrelations that overlaps with the EoR window and is suggestive of complex instrumental effects. Through systematic modeling on a single night of data, we find we can recover these modes in the power spectrum down to the integrated noise floor, achieving a dynamic range in the EoR window of 106 in power (mK2 units) with respect to the bright galactic foreground signal. Future work with deeper integrations will help determine whether these systematics can continue to be mitigated down to EoR levels. For future observing seasons, HERA will have upgraded analog and digital hardware to better control these systematics in the field.

Keywords: Cosmology, Reionization, Astronomy data analysis
Physical Models for the Clustering of Obscured and Unobscured Quasars. Clustering measurements of obscured and unobscured quasars show that obscured quasars reside in more massive dark matter halos than their unobscured counterparts. These results are inconsistent with simple unified (torus) scenarios but might be explained by models in which the distribution of obscuring material depends on Eddington ratio or galaxy stellar mass. We test these possibilities by constructing simple physical models to compare to observed active galactic nucleus populations. We find that previously observed relationships between obscuration and Eddington ratio or stellar mass are not sufficient to reproduce the observed quasar clustering results (&lt; {log}{M}halo}/{M}⊙ &gt; ={12.94}-0.11+0.10 and &lt; {log}{M}halo}/{M}⊙ &gt; ={12.49}-0.08+0.08 for obscured and unobscured populations, respectively) while maintaining the observed fraction of obscured quasars (30%-65%). This work suggests that evolutionary models, in which obscuration evolves on the typical timescale for black hole growth, are necessary to understand the observed clustering of mid-IR-selected quasars.

Keywords: AGN host galaxies, Quasars, Active galaxies, Clustering, Galaxy evolution
The Detection of Dust Gap-ring Structure in the Outer Region of the CR Cha Protoplanetary Disk. We observe the dust continuum at 225 GHz and CO isotopologue (12CO, 13CO, and C18O) J = 2-1 emission lines toward the CR Cha protoplanetary disk using the Atacama Large Millimeter/submillimeter Array. The dust continuum image shows a dust gap-ring structure in the outer region of the dust disk. A faint dust ring is also detected around 120 au beyond the dust gap. The CO isotopologue lines indicate that the gas disk is more extended than the dust disk. The peak brightness temperature of the 13CO line shows a small bump around 130 au, while 12CO lines do not. We investigate two possible mechanisms for reproducing the observed dust gap-ring structure and a gas temperature bump. First, the observed gap structure can be opened by a Jupiter-mass planet using the relation between the planet mass and the gap depth and width. Meanwhile, the radiative transfer calculations based on the observed dust surface density profile show that the observed dust ring could be formed by dust accumulation at the gas temperature bump, that is, the gas pressure bump produced beyond the outer edge of the dust disk.

Keywords: Observational astronomy, Proplyds
Varstrometry for Off-nucleus and Dual Subkiloparsec AGN (VODKA): Methodology and Initial Results with Gaia DR2. Gaia’s precision astrometry allows systematic identification of optically selected subkiloparsec dual active galactic nuclei (AGNs), off-nucleus AGNs, and small-scale lensed quasars by “varstrometry”—where variability-induced astrometric jitter, I.e., temporal displacements of photocenter in unresolved sources, can be reasonably well detected or constrained. This approach extends systematic searches for small-scale (≳mas) dual and off-nucleus AGNs to the poorly explored regime between ∼10 pc and ∼1 kpc, with Gaia’s full sky coverage and depth to G ∼ 21. We outline the general principles of this method and calculate the expected astrometric signals from the full time series of photocenter measurements and light curves. We demonstrate the feasibility of varstrometry by using Gaia Data Release 2 (DR2) data on a sample of variable pre-main-sequence stars with known close companions. We find that extended host galaxies have a significant impact on the accuracy of astrometric and photometric variability in Gaia DR2, a situation to be improved in future Gaia releases. Using spectroscopically confirmed Sloan Digital Sky Survey quasars, we present several examples of candidate subkiloparsec off-nucleus or dual AGNs selected from Gaia DR2. We discuss the merits and limitations of this method and a follow-up strategy for promising candidates. We highlight Gaia’s potential of systematically discovering and characterizing the subkiloparsec off-nucleus and dual AGN population in the entire optical sky.

Keywords: Double quasars, Quasars