adsabs/SciX_UAT_keywords huggingface dataset:
Dense Gas and Star Formation in Nearby Infrared-bright Galaxies: APEX Survey of HCN and HCO+ J = 2 → 1

Both Galactic and extragalactic studies of star formation suggest that stars form directly from dense molecular gas. To trace such high volume density gas, HCN and HCO+ J = 1 → 0 have been widely used for their high dipole moments, relatively high abundances, and often being the strongest lines after CO. However, HCN and HCO+ J = 1 → 0 emission could arguably be dominated by the gas components at low volume densities. The HCN J = 2 → 1 and HCO+ J = 2 → 1 transitions, with more suitable critical densities (1.6 × 106 and 2.8 × 105 cm-3) and excitation requirements, would trace typical dense gas closely related to star formation. Here we report new observations of HCN J = 2 → 1 and HCO+ J = 2 → 1 toward 17 nearby infrared-bright galaxies with the APEX 12 m telescope. The correlation slopes between the luminosities of HCN J = 2 → 1 and HCO+ J = 2 → 1 and total infrared emission are 1.03 ± 0.05 and 1.00 ± 0.05, respectively. The correlations of their surface densities, normalized with the area of radio/submillimeter continuum, show even tighter relations (slopes: 0.99 ± 0.03 and 1.02 ± 0.03). The eight active galactic nucleus (AGN)-dominated galaxies show no significant difference from the 11 star-formation-dominated galaxies in the above relations. The average HCN/HCO+ ratios are 1.15 ± 0.26 and 0.98 ± 0.42 for AGN- and star-formation-dominated galaxies, respectively, without obvious dependencies on infrared luminosity, dust temperature, or infrared pumping. The Magellanic Clouds roughly follow the same correlations, expanding to 8 orders of magnitude. On the other hand, ultraluminous infrared galaxies with AGNs systematically lie above the correlations, indicating potential biases introduced by AGNs.

Keywords: star formation; starburst galaxies; dense interstellar clouds; dust continuum emission; interstellar molecules
The Evolution of AGN Activity in Brightest Cluster Galaxies

We present the results of an analysis of Wide-field Infrared Survey Explorer (WISE) observations of the full 2500 deg2 South Pole Telescope (SPT)-Sunyaev-Zel'dovich cluster sample. We describe a process for identifying active galactic nuclei (AGN) in brightest cluster galaxies (BCGs) based on WISE mid-IR color and redshift. Applying this technique to the BCGs of the SPT-SZ sample, we calculate the AGN-hosting BCG fraction, which is defined as the fraction of BCGs hosting bright central AGNs over all possible BCGs. Assuming an evolving single-burst stellar population model, we find statistically significant evidence (>99.9%) for a mid-IR excess at high redshift compared to low redshift, suggesting that the fraction of AGN-hosting BCGs increases with redshift over the range of 0 < z < 1.3. The best-fit redshift trend of the AGN-hosting BCG fraction has the form (1 + z)4.1±1.0. These results are consistent with previous studies in galaxy clusters as well as as in field galaxies. One way to explain this result is that member galaxies at high redshift tend to have more cold gas. While BCGs in nearby galaxy clusters grow mostly by dry mergers with cluster members, leading to no increase in AGN activity, BCGs at high redshift could primarily merge with gas-rich satellites, providing fuel for feeding AGNs. If this observed increase in AGN activity is linked to gas-rich mergers rather than ICM cooling, we would expect to see an increase in scatter in the P cav versus L cool relation at z > 1. Last, this work confirms that the runaway cooling phase, as predicted by the classical cooling-flow model, in the Phoenix cluster is extremely rare and most BCGs have low (relative to Eddington) black hole accretion rates.

Keywords: galaxy clusters; galaxy evolution
Evidence for Ammonia-bearing Species on the Uranian Satellite Ariel Supports Recent Geologic Activity

We investigated whether ammonia-rich constituents are present on the surface of the Uranian moon Ariel by analyzing 32 near-infrared reflectance spectra collected over a wide range of sub-observer longitudes and latitudes. We measured the band areas and depths of a 2.2 μm feature in these spectra, which has been attributed to ammonia-bearing species on other icy bodies. Ten spectra display prominent 2.2 μm features with band areas and depths >2σ. We determined the longitudinal distribution of the 2.2 μm band, finding no statistically meaningful differences between Ariel's leading and trailing hemispheres, indicating that this band is distributed across Ariel's surface. We compared the band centers and shapes of the five Ariel spectra displaying the strongest 2.2 μm bands to laboratory spectra of various ammonia-bearing and ammonium-bearing species, finding that the spectral signatures of the Ariel spectra are best matched by ammonia-hydrates and flash frozen ammonia-water solutions. Our analysis also revealed that four Ariel spectra display 2.24 μm bands (>2σ band areas and depths), with band centers and shapes that are best matched by ammonia ice. Because ammonia should be efficiently removed over short timescales by ultraviolet photons, cosmic rays, and charged particles trapped in Uranus' magnetosphere, the possible presence of this constituent supports geologic activity in the recent past, such as emplacement of ammonia-rich cryolavas and exposure of ammonia-rich deposits by tectonism, impact events, and mass wasting.

Keywords: uranian satellites; surface ices; surface composition; planetary surfaces; surface processes
Discovery of 18 Stars with -3.10 < [Fe/H] < -1.45 in the Sagittarius Dwarf Galaxy

Studies of the early chemical evolution of some larger dwarf galaxies (>107 M⊙) are limited by the small number of stars known at low metallicities in these systems. Here we present metallicities and carbon abundances for eighteen stars with metallicities between -3.08 ≤ [Fe/H] ≤ -1.47 in the Sagittarius dwarf spheroidal galaxy, using medium-resolution spectra from the MagE spectrograph on the Magellan-Baade Telescope. This sample more than doubles the number of known very metal-poor stars ([Fe/H] ≤ -2.0) in the Sagittarius dwarf galaxy, and identifies one of the first known extremely metal-poor stars ([Fe/H] ≤ -3.0) in the system. These stars were identified as likely metal-poor members of Sagittarius using public, metallicity-sensitive photometry from SkyMapper DR1.1 and proper motion data from Gaia DR2, demonstrating that this dearth of metal-poor stars in some dwarf galaxies can be addressed with targeted searches using public data. We find that none of the stars in our sample are enhanced in carbon, in contrast to the relative prevalence of such stars in the Milky Way halo. Subsequent high-resolution spectroscopy of these stars would be key in detailing the early chemical evolution of the system. * This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Keywords: dwarf galaxies; sagittarius dwarf spheroidal galaxy; population ii stars
A Partial-sky Gibbs ILC Approach for the Estimation of CMB Posterior over Large Angular Scales of the Sky

In this article we present a formalism for incorporating the partial-sky maps into the Gibbs ILC algorithm to estimate the joint posterior density of the cosmic microwave background (CMB) signal and the theoretical CMB angular power spectrum given the observed CMB maps. In order to generate the partial-sky maps, we mask all the observed CMB maps provided by the WMAP and Planck satellite full-sky mission using a mask that removes 22% of the entire sky. The mask we use is based on the strength of the thermal dust emissions in the Planck 353 GHz map. While implementing the Gibbs ILC method on the partial-sky maps, we convert the partial-sky-cleaned angular power spectrum into the full-sky angular power spectrum using the mode-mode coupling matrix estimated from the smoothed mask. The main products of our analysis are a partial-sky cleaned best-fit CMB map and an estimate of the underlying full-sky theoretical CMB angular power spectrum in the multipole range 2 ≤ ℓ ≤ 32 along with their error estimates. We validate the method by performing detailed Monte Carlo simulations after using realistic models of foregrounds and detector noise consistent with the WMAP and Planck frequency channels used in our analysis. We can estimate the posterior density and full-sky theoretical CMB angular power spectrum without any need to explicitly model the foreground components from partial-sky maps using our method. Another important feature of this method is that the power spectrum results along with the error estimates can be directly used for cosmological parameter estimations.

Keywords: cosmic microwave background radiation
Radiative-dynamical Simulation of Jupiter's Stratosphere and Upper Troposphere

We present a two-dimensional radiative-dynamical model of the combined stratosphere and upper troposphere of Jupiter to understand its temperature distribution and meridional circulation pattern. Our study highlights the importance of radiative and mechanical forcing for driving the middle atmospheric circulation on Jupiter. Our model adopts a state-of-the-art radiative transfer scheme with recent observations of Jovian gas abundances and haze distribution. Assuming local radiative equilibrium, latitudinal variation of hydrocarbon abundances is not able to explain the observed latitudinal temperature variations in the mid-latitudes. With mechanical forcing parameterized as a frictional drag on zonal wind, our model produces ~2 K latitudinal temperature variations observed in low to mid-latitudes in the troposphere and lower stratosphere, but cannot reproduce the observed 5 K temperature variations in the middle stratosphere. In the high latitudes, temperature and meridional circulation depend strongly on polar haze radiation. The simulated residual mean circulation shows either two broad equator-to-pole cells or multi-cell patterns, depending on the frictional drag timescale and polar haze properties. A more realistic wave parameterization and a better observational characterization of haze distribution and optical properties are needed to better understand latitudinal temperature distributions and circulation patterns in the middle atmosphere of Jupiter.

Keywords: jupiter; atmospheric circulation; planetary atmospheres; planetary science; radiative transfer; solar system gas giant planets
Survey Operations for the Dark Energy Spectroscopic Instrument

The Dark Energy Spectroscopic Instrument (DESI) survey is a spectroscopic survey of tens of millions of galaxies at 0 < z < 3.5 covering 14,000 sq. deg. of the sky. In its first 1.1 yr of survey operations, it has observed more than 14 million galaxies and 4 million stars. We describe the processes that govern DESI's observations of the 15,000 fields composing the survey. This includes the planning of each night's observations in the afternoon; automatic selection of fields to observe during the night; real-time assessment of field completeness on the basis of observing conditions during each exposure; reduction, redshifting, and quality assurance of each field of targets in the morning following observation; and updates to the list of future targets to observe on the basis of these results. We also compare the performance of the survey with historical expectations and find good agreement. Simulations of the weather and of DESI observations using the real field-selection algorithm show good agreement with the actual observations. After accounting for major unplanned shutdowns, the dark time survey is progressing about 7% faster than forecast, which is good agreement given approximations made in the simulations.

Keywords: redshift surveys; spectroscopy; observatories
Pitch-angle Distributions of 0.5-1 GeV Solar Protons Crossing Earth's Orbit: Influence of the Large-scale Turbulent Interplanetary Magnetic Field

Using numerical simulations, we analyze the time evolution of the pitch-angle distribution of 500 MeV and 1 GeV solar protons, released impulsively near the Sun, at 1 au. The numerical model solves the equations of motion of an ensemble of particles that move in both the average Parker spiral field and a large-scale turbulent interplanetary magnetic field (IMF). Our model also includes the heliospheric current sheet (HCS). The focus of this study is to determine the effect of the large-scale turbulent IMF on the pitch-angle distribution of GV-rigidity protons and its time variations in terms of understanding variations in ground-level enhancement (GLE) events. Our particular interest is to explain the two distinct opposite-directed fluxes of the unusual event on 1989 October 22 (GLE#44). The results show that by adding the large-scale turbulence to the average Parker IMF, the pitch-angle distribution at 1 au depends strongly on the observer's location relative to the release location of the particles at the Sun. Even a 0.2° displacement in latitude or longitude leads to a significant change in the observed distribution and/or its variation in time. We find that there are some observer locations for which the distinct sunward and antisunward fluxes coexist at certain times of the events. We also find that the HCS has an important effect. For instance, even in locations of poor magnetic connection with the release location at the Sun, but near the HCS, there can be two fluxes moving in different directions at the same time.

Keywords: solar energetic particles
Theoretically Modeling Photoionized Regions with Fractal Geometry in Three Dimensions

We create a photoionization model embedded in the turbulent interstellar medium (ISM) by using the state-of-the-art Messenger Monte Carlo MAPPINGS V code (M3) in conjunction with the CMFGEN stellar atmosphere model. We show that the turbulent ISM causes the inhomogeneity of electron temperature and density within the nebula. The fluctuation in the turbulent ISM creates complex ionization structures seen in nearby nebulae. The inhomogeneous density distribution within the nebula creates a significant scatter on the spatially resolved standard optical diagnostic diagrams, which cannot be represented by the spherical constant-density photoionization model. We analyze the dependence of different optical emission lines on the complexity of nebular geometry, finding that the emission lines residing on the nebular boundary are highly sensitive to the complexity of nebular geometry, while the emission lines produced throughout the nebula are sensitive to the density distribution of the ISM within the nebula. Our fractal photoionization model demonstrates that a complex nebular geometry is required for the accurate modeling of H II regions and emission-line galaxies, especially for the high-redshift galaxies, where the ISM is highly turbulent based on increasing observational evidence.

Keywords: high-redshift galaxies; emission nebulae
Various Activities above Sunspot Light Bridges in IRIS Observations: Classification and Comparison

Light bridges (LBs) are among the most striking substructures in sunspots, where various activities have been revealed by recent high-resolution observations from the Interface Region Imaging Spectrograph (IRIS). Based on the variety of their physical properties, we classified these activities into four distinct categories: transient brightening (TB), intermittent jet (IJ), type-I light wall (LW-I), and type-II light wall (LW-II). In IRIS 1400/1330 Å observations, TBs are characterized by abrupt emission enhancements, and IJs appear as collimated plasma ejections with a width of 1-2 Mm at some LB sites. Most observed TBs are associated with IJs and show superpositions of some chromosphere absorption lines on enhanced and broadened wings of C II and Si IV lines, which could be driven by intermittent magnetic reconnection in the lower atmosphere. LW-I and LW-II are wall-shaped structures with bright fronts above the whole LB. An LW-I has a continuous oscillating front with a typical height of several Mm and an almost stationary period of 4-5 minutes. On the contrary, an LW-II has an indented front with a height of over 10 Mm, which has no stable period and is accompanied by recurrent TBs in the entire LB. These results support that LW-IIs are driven by frequent reconnection occurring along the entire LB due to large-scale magnetic flux emergence or intrusion, rather than the leakage of waves producing LW-Is. Our observations reveal a highly dynamical scenario of activities above LBs driven by different basic physical processes, including magnetoconvection, magnetic reconnection, and wave leakage.

Keywords: solar activity; solar atmosphere; solar magnetic reconnection; solar oscillations; sunspots; solar ultraviolet emission
[N II] Fine-structure Emission at 122 and 205 μm in a Galaxy at z = 2.6: A Globally Dense Star-forming Interstellar Medium

We present new observations with the Atacama Large Millimeter/submillimeter Array of the 122 and 205 μm fine-structure line emission of singly ionized nitrogen in a strongly lensed starburst galaxy at z = 2.6. The 122/205 μm [N II] line ratio is sensitive to electron density, ${n}_{{\rm{e}}}$, in the ionized interstellar medium, and we use this to measure ne ≈ 300 cm-3, averaged across the galaxy. This is over an order of magnitude higher than the Milky Way average, comparable to localized Galactic star-forming regions. Combined with observations of the atomic carbon (C I) and carbon monoxide (CO J = 4-3) in the same system, we reveal the conditions in this intensely star-forming system. The majority of the molecular interstellar medium has been driven to high density, and the resultant conflagration of star formation produces a correspondingly dense ionized phase, presumably colocated with myriad H II regions that litter the gas-rich disk.

Keywords: ultraluminous infrared galaxies; warm ionized medium; gravitational lensing
Efficient Detection and Characterization of Exoplanets within the Diffraction Limit: Nulling with a Mode-selective Photonic Lantern

Coronagraphs allow for faint off-axis exoplanets to be observed, but are limited to angular separations greater than a few beam widths. Accessing closer-in separations would greatly increase the expected number of detectable planets, which scales inversely with the inner working angle. The vortex fiber nuller (VFN) is an instrument concept designed to characterize exoplanets within a single beam width. It requires few optical elements and is compatible with many coronagraph designs as a complementary characterization tool. However, the peak throughput for planet light is limited to about 20%, and the measurement places poor constraints on the planet location and flux ratio. We propose to augment the VFN design by replacing its single-mode fiber with a six-port mode-selective photonic lantern, retaining the original functionality while providing several additional ports that reject starlight but couple planet light. We show that the photonic lantern can also be used as a nuller without a vortex. We present monochromatic simulations characterizing the response of the photonic lantern nuller (PLN) to astrophysical signals and wavefront errors, and show that combining exoplanet flux from the nulled ports significantly increases the overall throughput of the instrument. We show using synthetically generated data that the PLN detects exoplanets more effectively than the VFN. Furthermore, with the PLN, the exoplanet can be partially localized, and its flux ratio constrained. The PLN has the potential to be a powerful characterization tool complementary to traditional coronagraphs in future high-contrast instruments.

Keywords: coronagraphic imaging; exoplanet astronomy; direct imaging
YSE-PZ: A Transient Survey Management Platform that Empowers the Human-in-the-loop

The modern study of astrophysical transients has been transformed by an exponentially growing volume of data. Within the last decade, the transient discovery rate has increased by a factor of ~20, with associated survey data, archival data, and metadata also increasing with the number of discoveries. To manage the data at this increased rate, we require new tools. Here we present YSE-PZ, a transient survey management platform that ingests multiple live streams of transient discovery alerts, identifies the host galaxies of those transients, downloads coincident archival data, and retrieves photometry and spectra from ongoing surveys. YSE-PZ also presents a user with a range of tools to make and support timely and informed transient follow-up decisions. Those subsequent observations enhance transient science and can reveal physics only accessible with rapid follow-up observations. Rather than automating out human interaction, YSE-PZ focuses on accelerating and enhancing human decision making, a role we describe as empowering the human-in-the-loop. Finally, YSE-PZ is built to be flexibly used and deployed; YSE-PZ can support multiple, simultaneous, and independent transient collaborations through group-level data permissions, allowing a user to view the data associated with the union of all groups in which they are a member. YSE-PZ can be used as a local instance installed via Docker or deployed as a service hosted in the cloud. We provide YSE-PZ as an open-source tool for the community.

Keywords: supernovae; astronomy databases; astronomy web services; astronomy software; open source software; publicly available software; time domain astronomy; transient sources
The Spatial and Emission Properties of the Large [O III] Emission Nebula Near M31

Drechsler et al. reported the unexpected discovery of a 1.°5 long [O III] emission nebula 1.°2 southeast of the M31 nucleus. Here we present additional images of this large emission arc, called the Strottner-Drechsler-Sainty Object (SDSO), along with radial velocity and flux measurements from low-dispersion spectra. Independent sets of [O III] images show SDSO to be composed of broad streaks of diffuse emission aligned northeast-southwest. Deep Hα images reveal no strong coincident emission suggesting a high [O III]/Hα ratio. We also find no other [O III] emission nebulosity as bright as SDSO within several degrees of M31 and no filamentary Hα emission connected to SDSO. Optical spectra taken along the nebula's northern limb reveal [O III] λ λ4959, 5007 emissions matching the location and extent seen in our [O III] images. The heliocentric velocity of this [O III] nebulosity is -9.8 ± 6.8 km s-1 with a peak surface brightness of (4 ± 2) × 10-18 erg s-1 cm-2 arcsec-2 (~0.55 Rayleigh). We discuss SDSO as a possible unrecognized supernova remnant, a large and unusually nearby planetary nebula, a stellar bow shock nebula, or an interaction of M31's outer halo with Local Group circumgalactic gas. We conclude that galactic origins for SDSO are unlikely and favor instead an extragalactic M31 halo-circumgalactic cloud interaction scenario, despite the nebula's low radial velocity. We then describe new observations that may help resolve the nature and origin of this large nebulosity so close to M31 in the sky.

Keywords: circumgalactic medium