adsabs/SciX_UAT_keywords huggingface dataset:
Distribution of Water Vapor in Molecular Clouds. II

The depth-dependent abundance of both gas-phase and solid-state water within dense, quiescent, molecular clouds is important to both the cloud chemistry and gas cooling. Where water is in the gas phase, it is free to participate in the network of ion-neutral reactions that lead to a host of oxygen-bearing molecules, and its many ortho- and para-energy levels make it an effective coolant for gas temperatures greater than 20 K. Where water is abundant as ice on grain surfaces, and unavailable to cool the gas, significant amounts of oxygen are removed from the gas phase, suppressing the gas-phase chemical reactions that lead to a number of oxygen-bearing species, including O2. Models of far-UV (FUV)-illuminated clouds predict that the gas-phase water abundance peaks in the range AV ∼ 3 and 8 mag of the cloud surface, depending on the gas density and FUV field strength. Deeper within such clouds, water is predicted to exist mainly as ice on grain surfaces. More broadly, these models are used to analyze a variety of other regions, including outflow cavities associated with young stellar objects and the surface layers of protoplanetary disks. In this paper, we report the results of observational tests of FUV-illuminated cloud models toward the Orion Molecular Ridge and Cepheus B using data obtained from the Herschel Space Observatory and the Five College Radio Astronomy Observatory. Toward Orion, 2220 spatial positions were observed along the face-on Orion Ridge in the H2O 110- 101 557 GHz and NH3 J, K = 1,0-0,0 572 GHz lines. Toward Cepheus B, two strip scans were made in the same lines across the edge-on ionization front. These new observations demonstrate that gas-phase water exists primarily within a few magnitudes of dense cloud surfaces, strengthening the conclusions of an earlier study based on a much smaller data set, and indirectly supports the prediction that water ice is quite abundant in dense clouds.

Keywords: astrochemistry; interstellar abundances; interstellar molecules
Magnetic Reconnection as the Driver of the Solar Wind

We present EUV solar observations showing evidence for omnipresent jetting activity driven by small-scale magnetic reconnection at the base of the solar corona. We argue that the physical mechanism that heats and drives the solar wind at its source is ubiquitous magnetic reconnection in the form of small-scale jetting activity (a.k.a. jetlets). This jetting activity, like the solar wind and the heating of the coronal plasma, is ubiquitous regardless of the solar cycle phase. Each event arises from small-scale reconnection of opposite-polarity magnetic fields producing a short-lived jet of hot plasma and Alfvén waves into the corona. The discrete nature of these jetlet events leads to intermittent outflows from the corona, which homogenize as they propagate away from the Sun and form the solar wind. This discovery establishes the importance of small-scale magnetic reconnection in solar and stellar atmospheres in understanding ubiquitous phenomena such as coronal heating and solar wind acceleration. Based on previous analyses linking the switchbacks to the magnetic network, we also argue that these new observations might provide the link between the magnetic activity at the base of the corona and the switchback solar wind phenomenon. These new observations need to be put in the bigger picture of the role of magnetic reconnection and the diverse form of jetting in the solar atmosphere.

Keywords: solar corona; solar wind; magnetic fields; solar magnetic reconnection
IRIS Si IV Line Profiles at Flare Ribbons as Indications of Chromospheric Condensation

We present temporal variations of the Si IV line profiles at the flare ribbons in three solar flares observed by the Interface Region Imaging Spectrograph. In the M1.1 flare on 2014 September 6 and the X1.6 flare on 2014 September 10, the Si IV line profiles evolve from wholly redshifted to red-wing enhanced with the flare development. However, in the B1.8 flare on 2016 December 2, the Si IV line profiles are wholly redshifted throughout the flare evolution. We fit the wholly redshifted line profiles with a single-Gaussian function, but fit the red-asymmetric ones with a double-Gaussian function to deduce the corresponding Doppler velocities. In addition, we find that hard X-ray emission above 25 keV shows up in the two large flares, implying a nonthermal electron beam heating. In the microflare, there only appears weak hard X-ray emission up to 12 keV, indicative of a mostly thermal heating. We interpret the redshifts or red asymmetries of the Si IV line at the ribbons in the three flares as spectral manifestations of chromospheric condensation. We propose that whether the line appears to be wholly redshifted or red-asymmetric depends on the heating mechanisms, as well as on the propagation of the condensation.

Keywords: solar transition region; solar flares; solar ultraviolet emission; solar flare spectra
Predictions of Cosmic Microwave Background Foreground Dust Polarization Using Velocity Gradients

Observations of fluctuations in the cosmic microwave background provide information about primordial inhomogeneities in the universe. However, the B-mode polarization of the inflationary gravitational wave is contaminated by the Galactic foreground polarized radiation arising from dust aligned by interstellar magnetic fields. To trace magnetic fields, we use the Velocity Gradient Technique (VGT), which employs modern understanding of the nature of magnetohydrodynamic turbulent motions. In this paper, we combine the VGT with Principal Component Analysis (PCA) to improve the accuracy of magnetic field tracing. We apply the VGT-PCA to the high-resolution neutral hydrogen data from the GALFA-H I survey to predict the polarization of dust. We report that the predicted directions of dust polarization provide good correspondence with those reported by Planck 353 GHz, with the alignment measure between the two ≃0.79 ± 0.01. We show that our results statistically agree with the Planck polarization in terms of magnetic field tracing. We find that the variation of dust emission efficiency across the sky is small. Using our maps of predicted polarization, we calculate the ratio of the E- and B-modes, and show that BB/EE ≃ 0.53 ± 0.10, which is similar to the result from Planck polarization.

Keywords: interstellar magnetic fields; interstellar medium; cosmic microwave background radiation
Molecules with ALMA at Planet-forming Scales (MAPS): Complex Kinematics in the AS 209 Disk Induced by a Forming Planet and Disk Winds

We study the kinematics of the AS 209 disk using the J = 2-1 transitions of 12CO, 13CO, and C18O. We derive the radial, azimuthal, and vertical velocity of the gas, taking into account the lowered emission surface near the annular gap at ≃1.″7 (200 au) within which a candidate circumplanetary-disk-hosting planet has been reported previously. In 12CO and 13CO, we find a coherent upward flow arising from the gap. The upward gas flow is as fast as 150 m s-1 in the regions traced by 12CO emission, which corresponds to about 50% of the local sound speed or 6% of the local Keplerian speed. Such an upward gas flow is difficult to reconcile with an embedded planet alone. Instead, we propose that magnetically driven winds via ambipolar diffusion are triggered by the low gas density within the planet-carved gap, dominating the kinematics of the gap region. We estimate the ambipolar Elsässer number, Am, using the HCO+ column density as a proxy for ion density and find that Am is ~0.1 at the radial location of the upward flow. This value is broadly consistent with the value at which numerical simulations find that ambipolar diffusion drives strong winds. We hypothesize that the activation of magnetically driven winds in a planet-carved gap can control the growth of the embedded planet. We provide a scaling relationship that describes the wind-regulated terminal mass: adopting parameters relevant to 100 au from a solar-mass star, we find that the wind-regulated terminal mass is about one Jupiter mass, which may help explain the dearth of directly imaged super-Jovian-mass planets.

Keywords: planet formation; protoplanetary disks; radio interferometry
Detection of an Atmosphere on a Rocky Exoplanet

We report the detection of an atmosphere on a rocky exoplanet, GJ 1132 b, which is similar to Earth in terms of size and density. The atmospheric transmission spectrum was detected using Hubble WFC3 measurements and shows spectral signatures of aerosol scattering, HCN, and CH4 in a low mean molecular weight atmosphere. We model the atmospheric loss process and conclude that GJ 1132 b likely lost the original H/He envelope, suggesting that the atmosphere that we detect has been reestablished. We explore the possibility of H2 mantle degassing, previously identified as a possibility for this planet by theoretical studies, and find that outgassing from ultra-reduced magma could produce the observed atmosphere. In this way we use the observed exoplanet transmission spectrum to gain insights into magma composition for a terrestrial planet. The detection of an atmosphere on this rocky planet raises the possibility that the numerous powerfully irradiated super-Earth planets, believed to be the evaporated cores of sub-Neptunes, may, under favorable circumstances, host detectable atmospheres.

Keywords: extrasolar rocky planets; exoplanet atmospheres; exoplanets
Undermassive Host Galaxies of Five z ∼ 6 Luminous Quasars Detected with JWST

We measure host galaxy stellar masses for a sample of five luminous quasars at z ∼ 5–7. Using JWST/NIRCam medium-band images of nearby point-spread function reference stars, we carefully subtract the contribution from the quasar light to place upper and lower limits on the flux of each host galaxy. We find that the members of our sample of quasar host galaxies have mass upper limits of 109.7–1010.8 M ⊙, significantly less than expected from their supermassive black hole (SMBH) masses and the local M BH–M * relation. We additionally obtain JWST/NIRSpec integral field unit spectra of three of our quasars to calculate black hole masses, which we find are consistent with those in the literature, and to search for the presence of bright but compact galaxies via a Balmer break, for which we do not find evidence. We discuss the potential effects of dust extinction on our measured fluxes and the impact of selection effects on high-redshift quasar samples. We conclude that the masses of the SMBHs relative to the host galaxy stellar masses have a much larger scatter than locally, large enough that these selection effects cannot be responsible. This result is reinforced by other studies. Finally, we explore the potential implications of these results on the picture of SMBH–galaxy coeval growth in the early Universe.

Keywords: quasars; agn host galaxies; james webb space telescope
Gravitational Microlensing Event Statistics for the Zwicky Transient Facility

Microlensing surveys have discovered thousands of events, with almost all events discovered within the Galactic bulge or toward the Magellanic Clouds. The Zwicky Transient Facility (ZTF), while not designed to be a microlensing campaign, is an optical time-domain survey that observes the entire northern sky, including the Galactic plane, every few nights. The ZTF observes ∼109 stars in the g and r bands and can significantly contribute to the observed microlensing population. We predict that the ZTF will observe ∼1100 microlensing events in 3 yr of observing within 10° latitude of the Galactic plane, with ∼500 events in the outer Galaxy (ℓ ≥ 10°). This yield increases to ∼1400 (∼800) events by combining every three ZTF exposures, ∼1800 (∼900) events if the ZTF observes for a total of 5 yr, and ∼2400 (∼1300) events for a 5 yr survey with postprocessing image stacking. Using the microlensing modeling software PopSyCLE, we compare the microlensing populations in the Galactic bulge and the outer Galaxy. We also present an analysis of the microlensing event ZTF18abhxjmj to demonstrate how to leverage these population statistics in event modeling. The ZTF will constrain Galactic structure, stellar populations, and primordial black holes through photometric microlensing.

Keywords: stellar populations; time domain astronomy; microlensing event rate; milky way disk; bayesian statistics; stellar astronomy; milky way dark matter halo; transient sources; galactic bulge; gravitational microlensing; astronomy data modeling; black holes
JWST's PEARLS: Transients in the MACS J0416.1-2403 Field

With its unprecedented sensitivity and spatial resolution, the James Webb Space Telescope (JWST) has opened a new window for time-domain discoveries in the infrared. Here we report observations in the only field that has received four epochs (spanning 126 days) of JWST NIRCam observations in Cycle 1. This field is toward MACS J0416.1-2403, which is a rich galaxy cluster at redshift z = 0.4 and is one of the Hubble Frontier Fields. We have discovered 14 transients from these data. Twelve of these transients happened in three galaxies (with z = 0.94, 1.01, and 2.091) crossing a lensing caustic of the cluster, and these transients are highly magnified by gravitational lensing. These 12 transients are likely of a similar nature to those previously reported based on the Hubble Space Telescope (HST) data in this field, i.e., individual stars in the highly magnified arcs. However, these 12 could not have been found by HST because they were too red and too faint. The other two transients are associated with background galaxies (z = 2.205 and 0.7093) that are only moderately magnified, and they are likely supernovae. They indicate a demagnified supernova surface density, when monitored at a time cadence of a few months to a ~3-4 μm survey limit of AB ~28.5 mag, of ~0.5 arcmin-2 integrated to z ≈ 2. This survey depth is beyond the capability of HST but can be easily reached by JWST.

Keywords: transient sources; infrared sources; gravitational lensing; supernovae; surveys
Non-LTE Calculations of the Mg I 12.32 μm Line in a Flaring Atmosphere

The infrared Mg I lines near 12 μm are a pair of emission lines that are magnetically sensitive and have been used to measure solar magnetic fields. Here we calculate the response of the Mg I 12.32 μm line during a flare and find that in our modeling this line has a complicated behavior. At the beginning of the flare heating, this line shows an intensity dimming at the line center. The intensity then increases when heating continues, with increasing contributions from the heated layers in the chromosphere. The line formation height and the line width also increase as a result. As for the polarized line profiles, we find that flare heating tends to decrease the Zeeman splitting width and attenuates the Stokes V lobe intensity. The wider features in the Stokes V profiles are more pronounced during flare heating, which should be considered when performing magnetic field inversions.

Keywords: solar chromosphere; solar photosphere; radiative transfer simulations; solar flare spectra; infrared astronomy
Disintegration of Long-period Comet C/2019 Y4 (ATLAS). I. Hubble Space Telescope Observations

The near-Sun comet C/2019 Y4 (ATLAS) is the first member of a long-period comet group observed to disintegrate well before perihelion. Here we present our investigation into this disintegration event using images obtained in a three-day Hubble Space Telescope campaign. We identify two fragment clusters produced by the initial disintegration event, corresponding to fragments C/2019 Y4-A and C/2019 Y4-B identified in ground-based data. These two clusters started with similar integrated brightness but exhibit different evolutionary behavior. C/2019 Y4-A was much shorter-lived compared to C/2019 Y4-B and showed signs of significant mass loss and changes in size distribution throughout the three-day campaign. The cause of the initial fragmentation is undetermined by the limited evidence but crudely compatible with either the spin-up disruption of the nucleus or runaway sublimation of subsurface supervolatile ices, either of which would lead to the release of a large amount of gas as inferred from the significant bluing of the comet observed shortly before its disintegration. Gas can only be produced by the sublimation of volatile ices, which must have survived at least one perihelion passage at a perihelion distance of q = 0.25 au. We speculate that Comet ATLAS is derived from the ice-rich interior of a nonuniform, kilometer-wide progenitor that split during its previous perihelion. This suggests that comets down to a few kilometers in diameter can still possess complex, nonuniform interiors that can protect ices against intense solar heating.

Keywords: comet nuclei; comet interiors; comets; long period comets
Shocked Molecular Hydrogen and Broad CO Lines from the Interacting Supernova Remnant HB 3

We present the detections of shocked molecular hydrogen (H2) gas in near- and mid-infrared and broad CO in millimeter from the mixed-morphology supernova remnant (SNR) HB 3 (G132.7+1.3) using the Palomar Wide-field InfraRed Camera, the Spitzer GLIMPSE360 and Wide-field Infrared Survey Explorer (WISE) surveys, and the Heinrich Hertz Submillimeter Telescope. Our near-infrared narrow-band filter H2 2.12 μm images of HB 3 show that both Spitzer Infrared Array Camera and WISE 4.6 μm emission originates from shocked H2 gas. The morphology of H2 exhibits thin filamentary structures and a large scale of interaction sites between the HB 3 and nearby molecular clouds. Half of HB 3, the southern and eastern shell of the SNR, emits H2 in a shape of a butterfly or W, indicating the interaction sites between the SNR and dense molecular clouds. Interestingly, the H2 emitting region in the southeast is also co-spatial to the interacting area between HB 3 and the H II regions of the W3 complex, where we identified star-forming activity. We further explore the interaction between HB 3 and dense molecular clouds with detections of broad CO(3-2) and CO(2-1) molecular lines from the southern and southeastern shell along the H2 emitting region. The widths of the broad lines are 8-20 km s-1; the detection of such broad lines is unambiguous, dynamic evidence of the interactions between the SNR and clouds. The CO broad lines are from two branches of the bright, southern H2 shell. We apply the Paris-Durham shock model to the CO line profiles, which infer the shock velocities of 20-40 km s-1, relatively low densities of 103-4 cm-3, and strong (>200 μG) magnetic fields.

Keywords: co line emission; interstellar line emission; supernova remnants; nebulae; interstellar medium; line intensities; infrared telescopes; collisional broadening; infrared dark clouds; infrared observatories; molecular physics; core-collapse supernovae
Enhancing Triangulation of Interplanetary Type III Bursts through Wavevector Correction

Interplanetary Type III bursts, generated by relativistic electron beams at solar flare reconnection sites, are explored through an investigation of 152 instances observed by the Solar Terrestrial Relations Observatory mission. This study reveals that the absolute values of the wavevector deviations from the Sun-spacecraft line are statistically 3.72 and 2.10 larger than predicted by the density model, assuming fundamental and harmonic emission, respectively. Through Monte Carlo simulations, we examine the impact of scattering by density inhomogeneities on the apparent locations of radio emissions in the interplanetary medium. The findings indicate that relative density fluctuations of 0.40 can account for the observed angular shift, a conclusion supported by the multiple flux-tube solar wind model, which confirms the presence of such magnitude of relative perpendicular density fluctuations in the solar wind. We propose a wavevector correction that incorporates this effect to enhance the triangulation of interplanetary Type III bursts, demonstrating that radio triangulation, with this correction, can reliably track electron beams in the interplanetary medium.

Keywords: radio astronomy; radio bursts
The Vanishing and Appearing Sources during a Century of Observations Project. I. USNO Objects Missing in Modern Sky Surveys and Follow-up Observations of a “Missing Star”

In this paper we report the current status of a new research program. The primary goal of the “Vanishing and Appearing Sources during a Century of Observations” project is to search for vanishing and appearing sources using existing survey data to find examples of exceptional astrophysical transients. The implications of finding such objects extend from traditional astrophysics fields to the more exotic searches for evidence of technologically advanced civilizations. In this first paper we present new, deeper observations of the tentative candidate discovered by Villarroel et al. in 2016. We then perform the first searches for vanishing objects throughout the sky by comparing 600 million objects from the US Naval Observatory Catalogue (USNO) B1.0 down to a limiting magnitude of ∼20-21 with the recent Pan-STARRS Data Release-1 (DR1) with a limiting magnitude of ∼23.4. We find about 150,000 preliminary candidates that do not have any Pan-STARRS counterpart within a 30″ radius. We show that these objects are redder and have larger proper motions than typical USNO objects. We visually examine the images for a subset of about 24,000 candidates, superseding the 2016 study with a sample 10 times larger. We find about 100 point sources visible in only one epoch in the red band of the USNO, which may be of interest in searches for strong M-dwarf flares, high-redshift supernovae, or other categories of unidentified red transients.

Keywords: astrobiology; photographic photometry; surveys; transient sources; gamma-ray transient sources
Environmental Dependence of the Mass-Metallicity Relation in Cosmological Hydrodynamical Simulations

We investigate the environmental dependence of the gas-phase metallicity for galaxies at z = 0 to z ≳ 2 and the underlying physical mechanisms driving this dependence using state-of-the-art cosmological hydrodynamical simulations. We find that, at fixed stellar mass, central galaxies in massive halos have lower gas-phase metallicity than those in low-mass halos, while satellite galaxies residing in more massive halos are more metal-rich. The combined effect is that massive galaxies are more metal-poor in massive halos and low-mass galaxies are more metal-rich in massive halos. By inspecting the environmental dependence of other galaxy properties, we identify that the accretion of low-metallicity gas is responsible for the environmental dependence of central galaxies at high z, whereas the AGN feedback processes play a crucial role at low z. For satellite galaxies, we find that both the suppression of gas accretion and the stripping of existing gas are responsible for their environmental dependence, with negligible effect from the AGN feedback. Finally, we show that the difference of gas-phase metallicity as a function of stellar mass between protocluster and field galaxies agrees with recent observational results, for example from the MAMMOTH-Grism survey.

Keywords: protoclusters; galaxy evolution; galaxy formation; galaxy dark matter halos; galaxy groups