Sazuna/UAT_keywords huggingface dataset:
Dust Growth by Accretion of Molecules in Supersonic Interstellar Turbulence. We show that the growth rate of dust grains in cold molecular clouds is enhanced by the high degree of compressibility of a turbulent, dilute gas. By means of high-resolution (10243) numerical simulations, we confirm the theory that the spatial mean growth rate is proportional to the gas-density variance. This also results in broadening of the grain-size distribution (GSD) due to turbulence-induced variation of the grain-growth rate. We show, for the first time in a detailed numerical simulation of hydrodynamic turbulence, that the GSD evolves toward a shape that is a reflection of the gas-density distribution, regardless of the initial distribution. That is, in case of isothermal, rotationally forced turbulence, the GSD tends to be a lognormal distribution. We also show that in hypersonic turbulence, decoupling of gas and dust becomes important and that this leads to an even further accelerated grain growth.

Keywords: Interplanetary turbulence, Shocks, Interstellar dust processes
On the Evolution of the Globular Cluster System in NGC 1052-DF2: Dynamical Friction, Globular-Globular Interactions, and Galactic Tides. The ultradiffuse galaxy NGC 1052-DF2 has an overabundance of luminous globular clusters (GCs), and its kinematics is consistent with the presence of little to no dark matter. As the velocity dispersion among the GCs is comparable to the expected internal dispersions of the individual GCs, the galaxy might be highly conducive to GC-GC merging. If true, this could explain the puzzling luminosity function of its GCs. Here we examine this possibility by resimulating three of our earlier simulations of the GC system, where the GCs were modeled as single particles, with live GCs. Somewhat surprisingly, we infer a low merger rate of ∼0.03 Gyr-1. The main reason is that the GCs are too dense for tidal shock capture, caused by impulsive encounters among them, to operate efficiently (we infer a tidal capture rate of only ∼0.002 Gyr-1). Therefore, whatever mergers occur are driven by other mechanisms, which we find to be captures induced by dynamical friction and compressive tides from other GCs. The low merger rate inferred here makes it unlikely that the unusually large luminosities of the GCs can be explained as a result of past GC-GC mergers. Our simulations also indicate that, if NGC 1052-DF2 is indeed largely devoid of dark matter, its tidal field is too weak to induce any significant mass loss from the GCs. Therefore, in such a scenario, we predict that it is improbable for the GCs to reveal tidal features, something that can be tested with future deep observations.

Keywords: Globular star clusters, Dynamical friction, N-body simulations
The Mass-Metallicity Relation at z ≃ 8: Direct-method Metallicity Constraints and Near-future Prospects. Physical properties of galaxies at z &gt; 7 are of interest for understanding both the early phases of star formation and the process of cosmic reionization. Chemical abundance measurements offer valuable information on the integrated star formation history, and hence ionizing photon production, as well as the rapid gas accretion expected at such high redshifts. We use reported measurements of [O III] 88 μm emission and star formation rate to estimate gas-phase oxygen abundances in five galaxies at z = 7.1-9.1 using the direct ${T}_{{\rm{e}}}$ method. We find typical abundances $12+\mathrm{log}({\rm{O}}/{\rm{H}})$ = 7.9 (∼0.2 times the solar value) and an evolution of 0.9 ± 0.5 dex in oxygen abundance at fixed stellar mass from z ≃ 8 to 0. These results are compatible with theoretical predictions, albeit with large (conservative) uncertainties in both mass and metallicity. We assess both statistical and systematic uncertainties to identify promising means of improvement with the Atacama Large Millimeter/submillimeter Array (ALMA) and the James Webb Space Telescope (JWST). In particular we highlight [O III] 52 μm as a valuable feature for robust metallicity measurements. Precision of 0.1-0.2 dex in ${T}_{{\rm{e}}}$ -based O/H abundance can be reasonably achieved for galaxies at z ≈ 5-8 by combining [O III] 52 μm with rest-frame optical strong lines. It will also be possible to probe gas mixing and mergers via resolved ${T}_{{\rm{e}}}$ -based abundances on kiloparsec scales. With ALMA and JWST, direct metallicity measurements will thus be remarkably accessible in the reionization epoch.

Keywords: Reionization, High-redshift galaxies, Galaxy evolution, Galaxy chemical evolution
Toward Solving the Puzzle: Dissecting the Complex Merger A521 with Multiwavelength Data. A521 has been a subject of extensive panchromatic studies from X-ray to radio. The cluster possesses a number of remarkable features, including a bright radio relic with a steep spectrum, more than three distinct galaxy groups forming a filament, and two disturbed X-ray peaks at odds with the distant position and tilted orientation of the radio relic. These lines of evidence indicate a complex merger. In this paper, we present a multiwavelength study of A521 based on Subaru optical, Hubble Space Telescope infrared, Chandra X-ray, Giant Metrewave Radio Telescope radio, and Multiple Mirror Telescope optical spectroscopic observations. Our weak-lensing (WL) analysis with improved systematics control reveals that A521 is mainly composed of three substructures aligned in the northwest to southeast orientation. These WL mass substructures are remarkably well-aligned with the cluster optical luminosity distribution constructed from our new enhanced cluster member catalog. These individual substructure masses are determined by simultaneously fitting three Navarro-Frenk-White profiles. We find that the total mass of A521 modeled by the superposition of the three halos is ${13.0}_{-1.3}^{+1.0}\times {10}^{14}{M}_{\odot }$ , a factor of 2 higher than the previous WL measurement. With these WL mass constraints combined with X-ray and radio features, we consider two merging scenarios, carry out the corresponding numerical simulations, and discuss the strengths and weaknesses of each case.

Keywords: Galaxy clusters, Abell clusters, Intracluster medium, Gravitational lensing
Host Galaxy Properties and Offset Distributions of Fast Radio Bursts: Implications for Their Progenitors. We present observations and detailed characterizations of five new host galaxies of fast radio bursts (FRBs) discovered with the Australian Square Kilometre Array Pathfinder (ASKAP) and localized to ≲1″. Combining these galaxies with FRB hosts from the literature, we introduce criteria based on the probability of chance coincidence to define a subsample of 10 highly confident associations (at z = 0.03-0.52), 3 of which correspond to known repeating FRBs. Overall, the FRB-host galaxies exhibit a broad, continuous range of color (Mu - Mr = 0.9-2.0), stellar mass (M⋆ = 108 - 6 × 1010 M☉), and star formation rate (SFR = 0.05-10 M☉ yr-1) spanning the full parameter space occupied by z &lt; 0.5 galaxies. However, they do not track the color-magnitude, SFR-M⋆, nor BPT diagrams of field galaxies surveyed at similar redshifts. There is an excess of "green valley" galaxies and an excess of emission-line ratios indicative of a harder radiation field than that generated by star formation alone. From the observed stellar mass distribution, we rule out the hypothesis that FRBs strictly track stellar mass in galaxies (&gt;99% c.l.). We measure a median offset of 3.3 kpc from the FRB to the estimated center of the host galaxies and compare the host-burst offset distribution and other properties with the distributions of long- and short-duration gamma-ray bursts (LGRBs and SGRBs), core-collapse supernovae (CC-SNe), and SNe Ia. This analysis rules out galaxies hosting LGRBs (faint, star-forming galaxies) as common hosts for FRBs (&gt;95% c.l.). Other transient channels (SGRBs, CC-, and SNe Ia) have host-galaxy properties and offsets consistent with the FRB distributions. All of the data and derived quantities are made publicly available on a dedicated website and repository.

Keywords: Extragalactic radio sources, Radio bursts, Star formation, Interstellar medium, Magnetars, Galaxies
A Belt-like Distribution of Gaseous Hydrogen Cyanide on Neptune&amp;'s Equatorial Stratosphere Detected by ALMA. We present a spatially resolved map of integrated-intensity and abundance of Neptune&amp;'s stratospheric hydrogen cyanide (HCN). The analyzed data were obtained from the archived 2016 observation of the Atacama Large Millimeter/submillimeter Array. A 0"42 × 0"39 synthesized beam, which is equivalent to a latitudinal resolution of ∼20° at the disk center, was fine enough to resolve Neptune&amp;'s 2"24 diameter disk. After correcting the effect of different optical path lengths, a spatial distribution of HCN emissions is derived over Neptune&amp;'s disk, and it clearly shows a band-like HCN enhancement at the equator. Radiative transfer analysis indicates that the HCN volume mixing ratio measured at the equator was 1.92 ppb above the 10-3 bar pressure level, which is 40% higher than that measured at the southern middle and high latitudes. The spatial distribution of HCN can be interpreted as either the effect of the transportation of N2 from the troposphere by meridional atmospheric circulation, or an external supply such as cometary collisions (or both of these reasons). From the meridional circulation point of view, the observed HCN enhancement on both the equator and the pole can be explained by the production and accumulation of HCN at the downward branches of the previously suggested two-cell meridional circulation models. However, the HCN-depleted latitude of 60° S does not match with the location of the upward branch of the two-cell circulation models.

Keywords: Atmospheric composition, Submillimeter astronomy, Radio astronomy, Planetary atmospheres
Evolution of the Density PDF in Star-forming Clouds: The Role of Gravity. We derive an analytical theory of the PDF of density fluctuations in supersonic turbulence in the presence of gravity in star-forming clouds. The theory is based on a rigorous derivation of a combination of the Navier-Stokes continuity equations for the fluid motions and the Poisson equation for the gravity. It extends previous approaches, first by including gravity and second by considering the PDF as a dynamical system, not a stationary one. We derive the transport equations of the density PDF, characterize its evolution, and determine the density threshold above which gravity strongly affects and eventually dominates the dynamics of turbulence. We demonstrate the occurrence of two power-law tails in the PDF, with two characteristic exponents, corresponding to two different stages in the balance between turbulence and gravity. Another important result of this study is to provide a procedure to relate the observed column density PDFs to the corresponding volume density PDFs. This allows us to infer, from the observation of column densities, various physical parameters characterizing molecular clouds, notably the virial parameter. Furthermore, the theory offers the possibility to date the clouds in units of tcoll, the time since a statistically significant fraction of the cloud started to collapse. The theoretical results and diagnostics reproduce very well numerical simulations and observations of star-forming clouds. The theory provides a sound theoretical foundation and quantitative diagnostics to analyze observations or numerical simulations of star-forming regions and to characterize the evolution of the density PDF in various regions of molecular clouds.

Keywords: Star formation, Molecular clouds, Hydrodynamics
MeV Gamma Rays from Fission: A Distinct Signature of Actinide Production in Neutron Star Mergers. Neutron star mergers (NSMs) are the first verified sites of rapid neutron capture (r-process) nucleosynthesis, and could emit gamma rays from the radioactive isotopes synthesized in the neutron-rich ejecta. These MeV gamma rays may provide a unique and direct probe of the NSM environment as well as insight into the nature of the r process, just as observed gammas from the 56Ni radioactive decay chain provide a window into supernova nucleosynthesis. In this work, we include the photons from fission processes for the first time in estimates of the MeV gamma-ray signal expected from an NSM event. We consider NSM ejecta compositions with a range of neutron richness and find a dramatic difference in the predicted signal depending on whether or not fissioning nuclei are produced. The difference is most striking at photon energies above ∼3.5 MeV and at a relatively late time, several days after the merger event, when the ejecta is optically thin. We estimate that a Galactic NSM could be detectable by a next generation gamma-ray detector such as AMEGO in the MeV range, up to ∼104 days after the merger, if fissioning nuclei are robustly produced in the event.

Keywords: Nucleosynthesis, R-process, Compact binary stars, Supernovae, Gamma-ray transient sources, Gamma-rays
Discovery of a Fast-expanding Shell in the Inside-out Born-again Planetary Nebula HuBi 1 through High-dispersion Integral Field Spectroscopy. HuBi 1 has been proposed to be member of the rare class of born-again planetary nebulae (PNe), i.e., its central star experienced a very late thermal pulse and ejected highly processed material at high speeds inside the old hydrogen-rich PN. In this Letter we present GTC MEGARA integral field spectroscopic observations of the innermost regions of HuBi 1 at high spectral resolution ≃16 km s-1 and multi-epoch subarcsecond images obtained ≃12 yr apart. The analysis of these data indicates that the inner regions of HuBi 1 were ejected ≃200 yr ago and expand at velocities ≃300 km s-1, in excellent agreement with the born-again scenario. The unprecedented tomographic capabilities of the GTC MEGARA high-dispersion observations used here reveal that the ejecta in HuBi 1 has a shell-like structure, in contrast to the disrupted disk and jet morphology of the ejecta in other born-again PNe.

Keywords: Planetary nebulae, Jets, Interstellar medium, Stellar evolution
GW190521: Orbital Eccentricity and Signatures of Dynamical Formation in a Binary Black Hole Merger Signal. Pair-instability supernovae are thought to restrict the formation of black holes in the mass range $\sim 50\mbox{--}135\,{M}_{\odot }$ . However, black holes with masses within this "high mass gap" are expected to form as the remnants of binary black hole mergers. These remnants can merge again dynamically in densely populated environments such as globular clusters. The hypothesis that the binary black hole merger GW190521 formed dynamically is supported by its high mass. Orbital eccentricity can also be a signature of dynamical formation, since a binary that merges quickly after becoming bound may not circularize before merger. In this work, we measure the orbital eccentricity of GW190521. We find that the data prefer a signal with eccentricity $e\geqslant 0.1$ at 10 Hz to a nonprecessing, quasi-circular signal, with a log Bayes factor $\mathrm{ln}{ \mathcal B }=5.0$ . When compared to precessing, quasi-circular analyses, the data prefer a nonprecessing, $e\geqslant 0.1$ signal, with log Bayes factors $\mathrm{ln}{ \mathcal B }\approx 2$ . Using injection studies, we find that a nonspinning, moderately eccentric (e = 0.13) GW190521-like binary can be mistaken for a quasi-circular, precessing binary. Conversely, a quasi-circular binary with spin-induced precession may be mistaken for an eccentric binary. We therefore cannot confidently determine whether GW190521 was precessing or eccentric. Nevertheless, since both of these properties support the dynamical formation hypothesis, our findings support the hypothesis that GW190521 formed dynamically.

Keywords: Black holes, High energy astrophysics, Gravitational wave sources, Gravitational wave astronomy, Gravitational waves, Compact objects, Eccentricity, Dynamical evolution
Spitzer Reveals Evidence of Molecular Absorption in the Atmosphere of the Hot Neptune LTT 9779b. Non-rocky sub-Jovian exoplanets in high-irradiation environments are rare. LTT 9779b, also known as Transiting Exoplanet Survey Satellite (TESS) object of interest (TOI) 193.01, is one of the few such planets discovered to date, and the first example of an ultrahot Neptune. The planet&amp;'s bulk density indicates that it has a substantial atmosphere, so to investigate its atmospheric composition and shed further light on its origin, we obtained Spitzer InfraRed Array Camera secondary eclipse observations of LTT 9779b at 3.6 and 4.5 μm. We combined the Spitzer observations with a measurement of the secondary eclipse in the TESS bandpass. The resulting secondary eclipse spectrum strongly prefers a model that includes CO absorption over a blackbody spectrum, incidentally making LTT 9779b the first TESS exoplanet (and the first ultrahot Neptune) with evidence of a spectral feature in its atmosphere. We did not find evidence of a thermal inversion, at odds with expectations based on the atmospheres of similarly irradiated hot Jupiters. We also report a nominal dayside brightness temperature of 2305 ± 141 K (based on the 3.6 μm secondary eclipse measurement), and we constrained the planet&amp;'s orbital eccentricity to e &lt; 0.01 at the 99.7% confidence level. Together with our analysis of LTT 9779b&amp;'s thermal phase curves reported in a companion paper, our results set the stage for similar investigations of a larger sample of exoplanets discovered in the hot-Neptune desert, investigations that are key to uncovering the origin of this population.

Keywords: Eclipses, Sky surveys, Exoplanets, Hot Neptunes, Infrared astronomy, Exoplanet atmospheres
Phase Curves of Hot Neptune LTT 9779b Suggest a High-metallicity Atmosphere. Phase-curve measurements provide a global view of the composition, thermal structure, and dynamics of exoplanet atmospheres. Although most of the dozens of phase-curve measurements made to date are of large, massive hot Jupiters, there is considerable interest in probing the atmospheres of the smaller planets that are the more typical endproduct of the planet formation process. One such planet that is favorable for these studies is the ultrahot Neptune LTT 9779b, a rare denizen of the Neptune desert. A companion paper presents the planet&amp;'s secondary eclipses and dayside thermal emission spectrum; in this work we describe the planet&amp;'s optical and infrared phase curves, characterized using a combination of Spitzer and Transiting Exoplanet Survey Satellite (TESS) photometry. We detect LTT 9779b&amp;'s thermal phase variations at 4.5 μm, finding a phase amplitude of 358 ± 106 ppm and no significant phase offset, with a longitude of peak emission occurring -10° ± 21° east of the substellar point. Combined with our secondary eclipse observations, these phase-curve measurements imply a 4.5 μm dayside brightness temperature of 1800 ± 120 K, a nightside brightness temperature of 700 ± 430 K (&lt;1350 K at 2σ confidence), and a day-night brightness temperature contrast of 1110 ± 460 K. We compare our data to the predictions of 3D general circulation models calculated at multiple metallicity levels and to similar observations of hot Jupiters experiencing similar levels of stellar irradiation. Though not conclusive, our measurement of its small 4.5 μm phase offset, the relatively large amplitude of the phase variation, and the qualitative differences between our target&amp;'s dayside emission spectrum and those of hot Jupiters of similar temperatures all suggest a supersolar atmospheric metallicity for LTT 9779b, as might be expected given its size and mass. Finally, we measure the planet&amp;'s transits at both 3.6 μm and 4.5 μm, providing a refined ephemeris (P = 0.79207022 ± 0.00000069 days, T0 = 2458783.51636 ± 0.00027, BJDTDB) that will enable efficient scheduling of future observations to further characterize the atmosphere of this intriguing planet.

Keywords: Exoplanet atmospheres
The First Gamma-Ray Emitting BL Lacertae Object at the Cosmic Dawn. One of the major challenges in studying the cosmic evolution of relativistic jets is the identification of the high-redshift (z &gt; 3) BL Lacertae objects (BL Lacs), a class of jetted active galactic nuclei characterized by their quasi-featureless optical spectra. Here we report the identification of the first γ-ray emitting BL Lac, 4FGL J1219.0+3653 (J1219), beyond z = 3, i.e., within the first two billion years of the age of the universe. The optical and near-infrared spectra of J1219 taken from 10.4 m Gran Telescopio Canarias exhibit no emission lines down to an equivalent width of ∼3.5 Šsupporting its BL Lac nature. The detection of a strong Lyα break at ∼5570 Å, on the other hand, confirms that J2119 is indeed a high-redshift (z ∼ 3.59) quasar. Based on the prediction of a recent BL Lac evolution model, J1219 is one of the only two such objects expected to be present within the comoving volume at z = 3.5. Future identifications of more z &gt; 3 γ-ray emitting BL Lac sources, therefore, will be crucial to verify the theories of their cosmic evolution.

Keywords: BL Lacertae objects, Gamma-ray sources, Relativistic jets, Spectroscopy, High-redshift galaxies
Gamma-Ray and Radio Background Constraints on Cosmic Rays in Milky Way Circumgalactic Medium. We study the interaction of cosmic rays (CRs) with the diffuse circumgalactic gas of the Milky Way (MW) galaxy that results in hadronic γ-ray emission and radio synchrotron emission. We aim to constrain the CR population in our circumgalactic medium (CGM) with the help of the observed isotropic γ-ray background (IGRB), its anisotropy, and radio continuum. We modify different models of CGM gas in hydrostatic equilibrium discussed in the literature by including a cosmic-ray population, parameterized by η ≡ PCR/Pth. For the simplest isothermal model, while the IGRB intensity allows η ≲ 3, the anisotropy resulting from the solar system&amp;'s off-center position in MW rules out all values of η. For the precipitation model, in which the cooling of the CGM gas is regulated with an optimum ratio of cooling time to freefall time, while the observed IGRB intensity allows η ≲ 230, the observed anisotropy allows only very large values of η, of order ≳100. The radio continuum limits η ≲ 400 for the precipitation model and does not constrain the isothermal model; however, these constraints are mitigated by synchrotron loss time being comparable to CR diffusion timescales. These bounds are relevant for current numerical simulations that indicate a significant CR population in CGM of galaxies of MW mass.

Keywords: Diffuse radiation, Galactic cosmic rays, Milky Way Galaxy physics, Circumgalactic medium, Radio continuum emission, Gamma-rays