adsabs/SciX_UAT_keywords huggingface dataset:
CS Depletion in Prestellar Cores

The CS molecule is known to be adsorbed onto dust in cold and dense conditions, causing it to be significantly depleted in the central region of cores. This study is aimed to investigate the depletion of the CS molecule using the optically thin {C}34{S} molecular line observations. We mapped five prestellar cores, L1544, L1552, L1689B, L694-2, and L1197, using two molecular lines, {C}34S (J = 2 - 1) and {N}2{H}+ (J = 1 - 0) with the NRO 45 m telescope, doubling the number of cores where the CS depletion was probed using {C}34S . In most of our targets, the distribution of {C}34S emission shows features that suggest that the CS molecule is generally depleted in the center of the prestellar cores. The radial profile of the CS abundance with respect to {H}2 directly measured from the CS emission and the Herschel dust emission indicates that the CS molecule is depleted by a factor of ∼3 toward the central regions of the cores with respect to their outer regions. The degree of the depletion is found to be even more enhanced, by an order of magnitude, when the contaminating effect introduced by the presence of CS molecules in the surrounding envelope that lie along the line of sight is removed. Except for L1197—which is classified as relatively the least evolved core in our targets, based on its observed physical parameters—we found that the remaining four prestellar cores are suffering from significant CS depletion at their central region, regardless of the relative difference in their evolutionary status.

Keywords: interstellar molecules; abundance ratios; dense interstellar clouds; meridian circles; star forming regions; interstellar medium
Do LIGO/Virgo Black Hole Mergers Produce AGN Flares? The Case of GW190521 and Prospects for Reaching a Confident Association

The recent report of an association of the gravitational-wave (GW) binary black hole (BBH) merger GW190521 with a flare in the active galactic nuclei (AGNs) J124942.3 344929 has generated tremendous excitement. However, GW190521 has one of the largest localization volumes among all of the GW events detected so far. The 90 localization volume likely contains 7400 unobscured AGNs brighter than g 20.5 AB mag, and it results in a 70 probability of chance coincidence for an AGN flare consistent with the GW event. We present a Bayesian formalism to estimate the confidence of an AGN association by analyzing a population of BBH events with dedicated follow-up observations. Depending on the fraction of BBHs arising from AGNs, counterpart searches of ${ \mathcal O }(1)-{ \mathcal O }(100)$ GW events are needed to establish a confident association, and more than an order of magnitude more for searches without follow-up (i.e., using only the locations of AGN and GW events). Follow-up campaigns of the top 5 (based on volume localization and binary mass) of BBH events with total rest-frame mass 50 M are expected to establish a confident association during the next LIGO/Virgo/KAGRA observing run (O4), as long as the true value of the fraction of BBHs giving rise to AGN flares is >0.1. Our formalism allows us to jointly infer cosmological parameters from a sample of BBH events that include chance coincidence flares. Until the confidence of AGN associations is established, the probability of chance coincidence must be taken into account to avoid biasing astrophysical and cosmological constraints.

Keywords: gravitational wave astronomy; gravitational wave sources; gravitational waves; cosmology; active galactic nuclei; transient sources; high energy astrophysics; time domain astronomy
Finding Multiply Lensed and Binary Quasars in the DESI Legacy Imaging Surveys

The time delay between multiple images of strongly lensed quasars is a powerful tool for measuring the Hubble constant (H 0). To achieve H 0 measurements with higher precision and accuracy using the time delay, it is crucial to expand the sample of lensed quasars. We conduct a search for strongly lensed quasars in the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys. The DESI Legacy Surveys comprise 19,000 deg2 of the extragalactic sky observed in three optical bands (g, r, and z), making it well suited for the discovery of new strongly lensed quasars. We apply an autocorrelation algorithm to ~5 million objects classified as quasars in the DESI Quasar Sample. These systems are visually inspected and ranked. Here, we present 436 new multiply lensed and binary quasar candidates, 65 of which have redshifts from Sloan Digital Sky Survey Data Release 16. We provide redshifts for an additional 18 candidates from the SuperNova Integral Field Spectrograph.

Keywords: quasars; double quasars; gravitational lensing; strong gravitational lensing; hubble constant; galaxy evolution
Radio Study of the Pulsar Wind Nebula Powered by PSR B1706-44

PSR B1706-44 is an energetic gamma-ray pulsar located inside supernova remnant (SNR) G343.1-2.3 and it powers a compact pulsar wind nebula (PWN) that shows torus and jet structure in X-rays. We present a radio study of the PWN using Australia Telescope Compact Array observations at 3, 6, 13, and 21 cm. We found an overall arc-like morphology at 3 and 6 cm, and the "arc" shows two distinct peaks at 6 cm. The radio emission is faint inside the X-ray PWN and only brightens beyond that. We develop a thick torus model with Doppler boosting effect to explain the radio PWN structure. The model suggests a bulk flow speed of ~0.2c, which could indicate significant deceleration of the flow from the X-ray emitting region. Our polarization result reveals a highly ordered toroidal B field in the PWN. Its origin is unclear given that the supernova reverse shock should have interacted with the PWN. At a larger scale, the 13 and 21 cm radio images detected a semicircular rim and an east-west ridge of G343.1-2.3. We argue that the latter could possibly be a pulsar tail rather than a filament of the SNR, as supported by the flat radio spectrum and the alignment between the magnetic field and its elongation.

Keywords: pulsar wind nebulae; supernova remnants; polarimetry
Radio Continuum and Water Maser Observations of the High-mass Protostar IRAS 19035+0641 A

We present Very Large Array 1.3 cm continuum and 22.2 GHz H2O maser observations of the high-mass protostellar object IRAS 19035+0641 A. Our observations unveil an elongated bipolar 1.3 cm continuum structure at scales ≲500 au, which, together with a rising in-band spectral index, strongly suggests that the radio emission toward IRAS 19035+0641 A arises from an ionized jet. In addition, eight individual water maser spots well aligned with the jet axis were identified. The Stokes V spectrum of the brightest H2O maser line (∼100 Jy) shows a possible Zeeman splitting and is well represented by the derivatives of two Gaussian components fitted to the Stokes I profile. The measured B los are 123 (±27) and 156 (±8) mG, translating to a preshock magnetic field of ≈7 mG. Subsequent observations to confirm the Zeeman splitting showed intense variability in all the water maser spots, with the brightest maser completely disappearing. The observed variability in a 1 yr timescale could be the result of an accretion event. These findings strengthen our interpretation of IRAS 19035+0641 A as a high-mass protostar in an early accretion/outflow evolutionary phase.

Keywords: young stellar objects; water masers; radio jets
An Improved Prediction of Solar Cycles 25 and 26 Using the Informer Model: Gnevyshev Peaks and North–South Asymmetry

Forecasting the amplitude and timing of the sunspot cycle is highly important for solar physics and space weather applications, but high-precision prediction of solar magnetic activity has remained an outstanding challenge. The Informer model, as the most advanced deep learning technique, is an ideal approach for predicting solar activity cycle. Using the whole-disk sunspot numbers (SSNs) between 1749 and 2023 and the hemispheric SSNs between 1992 and 2023, the amplitudes and timings of Solar Cycles 25 and 26 are predicted by the Informer model. The main results are the following: (1) the activity levels of Solar Cycles 25 and 26 continue being weak-moderate cycles with their strengths stronger than Solar Cycle 24, implying that the long-term solar variability is significantly modulated in length and magnitude by the Gleissberg century cycle; (2) the Gnevyshev peaks of Solar Cycles 25 and 26 are clearly observed with a higher value in the second peak, suggesting that the numbers of the large sunspot groups are greater compared to the small sunspot groups in these two cycles; and (3) during Solar Cycle 25, the activity level in the southern hemisphere is predicted to be stronger than that in the northern one, revealing significant asymmetry and asynchronization between the two hemispheres. Our analysis results show that solar cycle predictions can be made more accurate if performed separately for each hemisphere. Furthermore, Solar Cycles 25 and 26 are likely to be weak-moderate cycles, in agreement with the precursor-based and model-based prediction methods.

Keywords: solar cycle; solar magnetic fields; solar activity
Growth of Supermassive Black Hole Seeds in ETG Star-forming Progenitors: Multiple Merging of Stellar Compact Remnants via Gaseous Dynamical Friction and Gravitational-wave Emission

We propose a new mechanism for the growth of supermassive black hole (BH) seeds in the star-forming progenitors of local early-type galaxies (ETGs) at z ≳ 1. This envisages the migration and merging of stellar compact remnants (neutron stars and stellar-mass BHs) via gaseous dynamical friction toward the central high-density regions of such galaxies. We show that, under reasonable assumptions and initial conditions, the process can build up central BH masses of the order of 104-106 M⊙ within some 107 yr, so effectively providing heavy seeds before standard disk (Eddington-like) accretion takes over to become the dominant process for further BH growth. Remarkably, such a mechanism may provide an explanation, alternative to super-Eddington accretion rates, for the buildup of billion-solar-massed BHs in quasar hosts at z ≳ 7, when the age of the universe ≲0.8 Gyr constitutes a demanding constraint; moreover, in more common ETG progenitors at redshift z ∼ 2-6, it can concur with disk accretion to build such large BH masses even at moderate Eddington ratios ≲0.3 within the short star formation duration ≲Gyr of these systems. Finally, we investigate the perspectives to detect the merger events between the migrating stellar remnants and the accumulating central supermassive BH via gravitational-wave emission with future ground- and space-based detectors such as the Einstein Telescope and the Laser Interferometer Space Antenna.

Keywords: quasars; dynamical friction; gravitational waves; galaxy evolution; astrophysical black holes
Maps of the Number of H I Clouds along the Line of Sight at High Galactic Latitude

Characterizing the structure of the Galactic interstellar medium (ISM) in three dimensions is of high importance for accurate modeling of dust emission as a foreground to the cosmic microwave background (CMB). At high Galactic latitude, where the total dust content is low, accurate maps of the 3D structure of the ISM are lacking. We develop a method to quantify the complexity of the distribution of dust along the line of sight with the use of H I line emission. The method relies on a Gaussian decomposition of the H I spectra to disentangle the emission from overlapping components in velocity. We use this information to create maps of the number of clouds along the line of sight. We apply the method to (a) the high Galactic latitude sky and (b) the region targeted by the BICEP/Keck experiment. In the north Galactic cap we find on average three clouds per 0.2 square degree pixel, while in the south the number falls to 2.5. The statistics of the number of clouds are affected by intermediate-velocity clouds (IVCs), primarily in the north. IVCs produce detectable features in the dust emission measured by Planck. We investigate the complexity of H I spectra in the BICEP/Keck region and find evidence for the existence of multiple components along the line of sight. The data (doi: 10.7910/DVN/8DA5LH) and software are made publicly available and can be used to inform CMB foreground modeling and 3D dust mapping.

Keywords: interstellar medium; neutral hydrogen clouds; interstellar atomic gas
A New "Non-energetic" Route to Complex Organic Molecules in Astrophysical Environments: The C + H2O → H2CO Solid-state Reaction

The solid-state reaction C + H2O → H2CO was studied experimentally following the co-deposition of C atoms and H2O molecules at low temperatures. In spite of the reaction barrier and absence of energetic triggering, the reaction proceeds fast on the experimental timescale pointing to its quantum tunneling mechanism. This route to formaldehyde shows a new "non-energetic" pathway to complex organic and prebiotic molecules in astrophysical environments. Energetic processing by UV irradiation of the ice produced by co-deposition of C and H2O reactants leads mainly to the destruction of H2CO and the formation of CO2, challenging the role of energetic processing in the synthesis of complex organic molecules under astrophysically relevant conditions.

Keywords: astrochemistry; surface processes
Reflected Spectroscopy of Small Exoplanets II: Characterization of Terrestrial Exoplanets

A space telescope capable of high-contrast imaging has been recognized as the avenue toward finding terrestrial planets around nearby Sun-like stars and characterizing their potential habitability. It is thus essential to quantify the capability of reflected light spectroscopy obtained through direct imaging for terrestrial exoplanets, and existing work focused on planetary analogs of modern Earth. Here we go beyond Earth analogs and use a Bayesian retrieval algorithm, EXOREL ${}^{{\mathfrak{R}}}$ , to determine what we could learn about terrestrial exoplanets from their reflected light spectra. Recognizing the potential diversity of terrestrial exoplanets, our focus is to distinguish atmospheric scenarios without any a priori knowledge of the dominant gas. We find that, while a moderate-resolution spectrum in the optical band (0.4-1.0 μm) may sufficiently characterize a modern Earth analog, it would likely result in incorrect interpretation for planets similar to Archean Earth or having CO2-dominated atmospheres. Including observations in the near-infrared bands (1.0-1.8 μm) can prevent this error, determine the main component (N2, O2, or CO2), and quantify trace gases (H2O, O3, and CH4) of the atmosphere. These results are useful to define the science requirements and design the wavelength bandwidth and observation plans of exoplanet direct imaging missions in the future.

Keywords: exoplanet atmospheric composition; exoplanet atmospheres; bayesian statistics; bayes' theorem; posterior distribution; prior distribution; extrasolar rocky planets
Evidence for an Outer Component in the Continuum Reverberation Mapping of Active Galactic Nuclei

Continuum reverberation mapping is widely used in studying the accretion disks of active galactic nuclei (AGNs). Some indirect evidence and simulations have indicated that the diffuse continuum, especially the strong Balmer continuum from the broad-line region, may contribute to the continuum in the u/U band. Here, we present direct evidence for this contribution. In this work, we apply the ICCF-Cut method to continuum reverberation mapping to extract the possible diffuse continuum light curves of six AGNs, using high-cadence, high-quality, and multiband observations. We find the existence of an outer component out of the accretion disk for each of the six AGNs in the Swift U band. Meanwhile, similar results can be derived with the JAVELIN Photometric Reverberation Mapping Model for four of them. The lags of the outer components are consistent with the predicted Balmer continuum lags, which are about half of the Hβ lag values. Our result directly reinforces the understanding that an outer component, especially the Balmer continuum in the rest-frame u/U band, can contribute significantly to the continuum reverberation lags of AGNs.

Keywords: reverberation mapping; active galactic nuclei; supermassive black holes
A Case against a Significant Detection of Precession in the Galactic Warp

Recent studies of warp kinematics using Gaia DR2 data have produced detections of warp precession for the first time, which greatly exceeds theoretical predictions of models. However, this detection assumes a warp model derived for a young population (few tens of megayears) to fit velocities of an average older stellar population of the thin disk (several gigayears) in Gaia-DR2 observations, which may lead to unaccounted systematic errors. Here, we recalculate the warp precession with the same approach and Gaia DR2 kinematic data, but using different warp parameters based on the fit of star counts of the Gaia DR2 sample, which has a much lower warp amplitude than the young population. When we take into account this variation of the warp amplitude with the age of the population, we find that there is no need for precession. We find the value of warp precession $\beta ={4}_{-4}^{+6}$ km s-1 kpc-1, which does not exclude nonprecessing warp.

Keywords: milky way disk; milky way galaxy
Supermassive Black Holes as Possible Sources of Ultrahigh-energy Cosmic Rays

The production and acceleration mechanisms of ultrahigh-energy cosmic rays (UHECRs) of energy >1020 eV, clearly beyond the GZK cutoff limit, remain unclear, which points to the exotic nature of the phenomena. Recent observations of extragalactic neutrinos may indicate that the source of UHECRs is an extragalactic supermassive black hole (SMBH). We demonstrate that ultraefficient energy extraction from a rotating SMBH driven by the magnetic Penrose process (MPP) could indeed fit the bill. We envision ionization of neutral particles, such as neutron beta decay, skirting close to the black hole horizon that energizes protons to over 1020 eV for an SMBH of mass 109M⊙ and magnetic field 104 G. Applied to the Galactic center SMBH, we have a proton energy of order ≈1015.6 eV that coincides with the knee of the cosmic-ray spectra. We show that large γz factors of high-energy particles along the escaping directions occur only in the presence of an induced charge of the black hole, which is known as the Wald charge in the case of a uniform magnetic field. It is remarkable that the process requires neither an extended acceleration zone nor fine-tuning of accreting-matter parameters. Further, this leads to certain verifiable constraints on the SMBH's mass and magnetic field strength as the source of UHECRs. This clearly makes the ultraefficient regime of the MPP one of the most promising mechanisms for fueling the UHECR powerhouse.

Keywords: black hole physics; high energy astrophysics
The Stellar Mass Function in CANDELS and Frontier Fields: The Buildup of Low-mass Passive Galaxies since z 3

Despite significant efforts in recent years, the physical processes responsible for the formation of passive galaxies through cosmic time remain unclear. The shape and evolution of the stellar mass function (SMF) give an insight into these mechanisms. Taking advantage of the CANDELS and the deep Hubble Frontier Fields (HFF) programs, we estimated the SMF of total, star-forming, and passive galaxies from z = 0.25 to z = 2.75 to unprecedented depth and we focus on the latter population. The density of passive galaxies underwent a significant evolution over the last 11 Gyr. They account for 60% of the total mass in the nearby universe against ~20% observed at z ~ 2.5. The inclusion of the HFF program allows us to detect, for the first time at z > 1.5, the characteristic upturn in the SMF of passive galaxies at low masses, usually associated with environmental quenching. We observe two separate populations of passive galaxies evolving on different timescales: roughly half of the high-mass systems were already quenched at high redshift, while low-mass passive galaxies are gradually building up over the redshift range probed. In the framework of environmental quenching at low masses, we interpret this finding as evidence of an increasing role of the environment in the buildup of passive galaxies as a function of time. Finally, we compared our findings with a set of theoretical predictions. Despite good agreement in some redshift and mass intervals, none of the models are able to fully reproduce the observations. This calls for further investigation into the involved physical mechanisms, both theoretically and observationally, especially with the brand-new JWST data.

Keywords: galaxy evolution; stellar mass functions; astronomy data analysis; high-redshift galaxies; quenched galaxies
Jump-starting Relativistic Flows and the M87 Jet

We point out the dominant importance of plasma injection effects of relativistic winds from pulsars and black holes. We demonstrate that outside the light cylinder, the magnetically dominated outflows sliding along the helical magnetic field move nearly radially with very large Lorentz factors, γ 0 ≫ 1, imprinted into the flow during pair production within the gaps. Only at larger distances, r ≥ γ 0(c/Ω), does MHD acceleration Γ ∝ r take over. As a result, Blandford–Znajek (BZ)-driven outflows produce spine-brightened images. The best-resolved case of the jet in M87 shows both edge-brightened features, as well as weaker spine-brightened features. Only the spine-brightened component can be BZ driven/originate from the black hole's magnetosphere.

Keywords: relativistic jets
New Covariant Density Functionals of Nuclear Matter for Compact Star Simulations

We generate three families of extended covariant density functionals of nuclear matter that have varying slope of symmetry energy and skewness at nuclear saturation density, but otherwise share the same basic parameters (symmetry energy, compressibility, saturation parameters, etc.) with the standard DDME2, DD2, and MPE functionals. Tables of the parameters of these new density functionals are given, which can be straightforwardly used in DDME2, DD2, and MPE parameterization-based codes. Furthermore, we provide tables of a large number of equations of state (81 for each family) that can be used in astrophysical simulations to assess the impact of variations of the not-well-known slope of symmetry energy and skewness of nuclear systems on the astrophysics of compact objects. We also provide tables of computed integral parameters (mass, radius, and tidal deformability) that can be used, e.g., for modeling gravitational waveforms. Finally, for the extended DDME2-based parameterization, we implement a first-order phase transition to quark matter to obtain a family of equations of state that accommodates a phase transition to quark matter. Analogous tables of the equations of state and integral parameters are provided for this case as well.

Keywords: high energy astrophysics; neutron star cores; nuclear astrophysics
A Spatially-resolved Large Cavity of the J0337 Protoplanetary Disk in Perseus

We present Keck/NIRC2 K p L p high-contrast imaging observations of a J0337 protoplanetary disk. The data discover the spatially-resolved large cavity, which is the second report among protoplanetary disks in the Perseus star-forming region after the LkHα 330 system. Our data and forward modeling using RADMC-3D suggests ~80 au for the cavity radius. There is discrepancy between J0337's spectral energy distribution (SED) and the modeled SED at ~10 μm and this suggests an unseen inner disk. We also searched for companions around J0337 but did not detect any companion candidates at separations between 0.″1 and 2.″5. The L p-band detection limit corresponds to ~20M Jup at 60 au, ~9-10M Jup at 90 au, and ~3M Jup at >120 au. Compared with other young systems with large cavities such as PDS 70 and RX J1604, multiple Jovian planets, a single eccentric Jovian planet, or a massive brown dwarf at an inner separation could exist within the cavity.

Keywords: protoplanetary disks; planet formation