adsabs/SciX_UAT_keywords huggingface dataset:
On the Shape of SEP Electron Spectra: The Role of Interplanetary Transport

We address the effect of particle scattering on the energy spectra of solar energetic electron events using (I) an observational and (II) a modeling approach. (I) We statistically study observations of the STEREO spacecraft, using directional electron measurements made with the Solar Electron and Proton Telescope in the range of 45-425 keV. We compare the energy spectra of the anti-Sunward propagating beam with that of the backward-scattered population and find that, on average, the backward-scattered population shows a harder spectrum with the effect being stronger at higher energies. (II) We use a numerical solar energetic particle (SEP) transport model to simulate the effect of particle scattering (both in terms of pitch angle and perpendicular to the mean field) on the spectrum. We find that pitch-angle scattering can lead to spectral changes at higher energies (E > 100 keV) and further away from the Sun (r > 1 au), which are also often observed. At lower energies, and closer to the Sun, the effect of pitch-angle scattering is much more reduced, so that the simulated energy spectra still resemble the injected power-law functions. When examining pitch-angle-dependent spectra, we find, in agreement with the observational results, that the spectra of the backward-propagating electrons are harder than that of the forward (from the Sun) propagating population. We conclude that Solar Orbiter and Parker Solar Probe will be able to observe the unmodulated omnidirectional SEP electron spectrum close to the Sun at higher energies, giving a direct indication of the accelerated spectrum.

Keywords: interplanetary turbulence; the sun; solar energetic particles
Dust and Cold Gas Properties of Starburst HyLIRG Quasars at z ∼ 2.5

Some high-z active galactic nuclei (AGNs) are found to reside in extreme star-forming galaxies, such as hyperluminous infrared galaxies (HyLIRGs), with AGN-removed L IR of >1013 L ⊙. In this paper, we report NOEMA observations of six apparent starburst HyLIRGs associated with optical quasars at z ∼ 2–3 in the Stripe 82 field, to study their dust and molecular CO properties. Five out of the six candidates are detected with CO(4–3) or CO(5–4) emission, and four in the 2 mm dust continuum. Based on the linewidth– ${L}_{\mathrm{CO}(1-0)}^{{\prime} }$ diagnostics, we find that four galaxies are likely unlensed or weakly lensed sources. The molecular gas mass is in the range of $\mu {M}_{{{\rm{H}}}_{2}}\,\sim 0.8\mbox{-}9.7\times {10}^{10}\,{M}_{\odot }$ (with $\alpha =0.8\,{M}_{\odot }{\left({\rm{K}}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{pc}}^{2}\right)}^{-1}$ , where μ is the unknown possible gravitational magnification factor). We fit their spectral energy distributions, after including the observed 2 mm fluxes and upper limits, and estimate their apparent (uncorrected for possible lensing effects) star formation rates (μSFRs) to be ∼400–2500 M ⊙ yr‑1, with a depletion time of ∼20–110 Myr. We notice interesting offsets, of ∼10–40 kpc spatially or ∼1000–2000 km s‑1 spectroscopically, between the optical quasar and the millimeter continuum or CO emissions. The observed velocity shift is likely related to the blueshifted broad-emission-line region of quasars, though mergers or recoiling black holes are also possible causes, which can explain the spatial offsets and the high intrinsic star formation rates in the HyLIRG quasar systems.

Keywords: starburst galaxies; co line emission; millimeter-wave spectroscopy; interferometry; quasars; galaxy evolution
The Relationship of Supermassive Black Holes and Host Galaxies at z < 4 in the Deep Optical Variability-selected Active Galactic Nuclei Sample in the COSMOS Field

We present the study on the relationship between supermassive black holes (SMBHs) and their host galaxies using our variability-selected active galactic nuclei (AGNs) sample (i AB ≤ 25.9 and z ≤ 4.5) constructed from the Hyper Suprime-Cam Subaru Strategic Program Ultradeep survey in the COSMOS field. We estimated the black hole (BH) mass (M BH = 105.5‑10 M ⊙) based on the single-epoch virial method and the total stellar mass (M star = 1010‑12 M ⊙) by separating the AGN component with spectral energy distribution fitting. We found that the redshift evolution of the BH–stellar mass ratio (M BH/M star) depends on the M BH, which is caused by no significant correlation between M BH and M star. Variable AGNs with massive SMBHs (M BH > 109 M ⊙) at 1.5 < z < 3 show considerably higher BH–stellar mass ratios (> ∼1%) than the BH–bulge ratios (M BH/M bulge) observed in the local Universe for the same BH range. This implies that there is a typical growth path of massive SMBHs, which is faster than the formation of the bulge component as final products seen in the present day. For the low-mass SMBHs (M BH < 108 M ⊙) at 0.5 < z < 3, on the other hand, variable AGNs show similar BH–stellar mass ratios with the local objects (∼0.1%), but smaller than those observed at z > 4. We interpret that host galaxies harboring less massive SMBHs at intermediate redshift have already acquired sufficient stellar mass, although high-z galaxies are still in the early stage of galaxy formation relative to those at the intermediate/local Universe.

Keywords: active galactic nuclei; supermassive black holes; black hole physics; seyfert galaxies
Magnetar XTE J1810-197: Spectro-temporal Evolution of Average Radio Emission

We present the long-term spectro-temporal evolution of the average radio emission properties of the magnetar XTE J1810-197 (PSR J1809-1943), following its most recent outburst in late 2018. We report the results from a 2.5 yr monitoring campaign with the upgraded Giant Metrewave Radio Telescope, carried out over the frequency range of 300-1450 MHz. Our observations show intriguing time variability in the average profile width, flux density, spectral index, and broadband spectral shape. While the average profile width appears to gradually decrease at later epochs, the flux density shows multiple episodes of radio rebrightening over the course of our monitoring. Our systematic monitoring observations reveal that the radio spectrum has steepened over time, resulting in evolution from a magnetar-like spectrum to a more pulsar-like spectrum. A more detailed analysis reveals that the radio spectrum has a turnover, and that this turnover shifts toward lower frequencies with time. We present the details of our analysis leading to these results, and discuss our findings in the context of magnetar radio emission mechanisms, as well as potential manifestations of the intervening medium. We also briefly discuss whether an evolving spectral turnover could be a ubiquitous property of radio magnetars.

Keywords: magnetars; radio pulsars; rotation powered pulsars; neutron stars; non-thermal radiation sources; interstellar absorption; interstellar medium; radio transient sources; radio bursts; pulsars; soft gamma-ray repeaters
Evidence for the Accretion of Gas in Star-forming Galaxies: High N/O Abundances in Regions of Anomalously Low Metallicity

While all models for the evolution of galaxies require the accretion of gas to sustain their growth via on-going star formation, it has proven difficult to directly detect this inflowing material. In this paper we use data of nearby star-forming galaxies in the SDSS IV Mapping Nearby Galaxies at Apache Point Observatory survey to search for evidence of accretion imprinted in the chemical composition of the interstellar medium. We measure both the O/H and N/O abundance ratios in regions previously identified as having anomalously low values of O/H. We show that the unusual locations of these regions in the N/O versus O/H plane indicate that they have been created through the mixing of disk gas having higher metallicity with accreted gas having lower metallicity. Taken together with previous analysis on these anomalously low-metallicity regions, these results imply that accretion of metal-poor gas can probably sustain star formation in present-day late-type galaxies.

Keywords: galaxy abundances; galaxy physics; surveys; spectroscopy
Comet-like Activity Discovered on Quasi-Hilda Asteroid 2009 DQ118

We report evidence of comet-like activity on asteroid 2009 DQ118, a quasi-Hilda object near the 3:2 interior mean-motion resonance with Jupiter. This discovery was made by volunteers as part of the Active Asteroids Citizen Science project, a NASA Partner hosted on the Zooniverse platform. Follow-up archival searches yielded over 20 images of 2009 DQ118 exhibiting a comet-like tail on UT 2016 March 8 and 9 acquired with the Dark Energy Camera on the Blanco 4 m telescope at the Cerro Tololo Inter-American Observatory, Chile. These images were taken when 2009 DQ118 was near its 2016 perihelion passage. 2009 DQ118 will next reach perihelion on UT 2023 April 22; hence, the next several months are an excellent time to observe 2009 DQ118 to search for a second epoch of activity for this object.

Keywords: asteroids; comae; comet tails; hilda group
AMBER: A Semi-numerical Abundance Matching Box for the Epoch of Reionization

The Abundance Matching Box for the Epoch of Reionization (AMBER) is a semi-numerical code for modeling the cosmic dawn. The new algorithm is not based on the excursion set formalism for reionization, but takes the novel approach of calculating the reionization-redshift field ${z}_{\mathrm{re}}({\boldsymbol{x}})$ assuming that hydrogen gas encountering higher radiation intensity are photoionized earlier. Redshift values are assigned while matching the abundance of ionized mass according to a given mass-weighted ionization fraction ${\bar{x}}_{{\rm{i}}}(z)$ . The code has the unique advantage of allowing users to directly specify the reionization history through the redshift midpoint z mid, duration Δz, and asymmetry A z input parameters. The reionization process is further controlled through the minimum halo mass M min for galaxy formation and the radiation mean free path l mfp for radiative transfer. We implement improved methods for constructing density, velocity, halo, and radiation fields, which are essential components for modeling reionization observables. We compare AMBER with two other semi-numerical methods and find that our code more accurately reproduces the results from radiation-hydrodynamic simulations. The parallelized code is over four orders of magnitude faster than radiative transfer simulations and will efficiently enable large-volume models, full-sky mock observations, and parameter-space studies. AMBER will be made publicly available to facilitate and transform studies of the Epoch of Reionization.

Keywords: cosmology; reionization; intergalactic medium; large-scale structure of the universe; computational methods
Period–Luminosity–Metallicity–Color Relations of Late-type Contact Binaries in the Big Data Era

Binary stars ubiquitous throughout the Universe are important. Contact binaries (CBs) possessing period–luminosity (PL) relations could be adopted as distance tracers. The PL relations of CBs are influenced by metallicity abundance and color index, which are connected to both the radius and luminosity of stars. Here we propose fine relations of the period–luminosity–metallicity–color (PLZC) from the ultraviolet to infrared bands based on current surveys. The accuracy of the distance estimation is 6% and 8%, respectively, depending on the PLZC relations of the CBs in the infrared and optical bands of the collected data. PLZC models are still more accurate than PLC models in determining intrinsic luminosity, notwithstanding their limited improvement. Meanwhile, these relations based on synthetic photometry are also calibrated. On the basis of the synthetic photometry, a 6% accuracy of distance is estimated. The measured or synthetic data of PLZC or PLC relations in infrared bands comes first in the list of suggestions for distance estimations and is followed by the measured data of optical bands.

Keywords: binary stars; catalogs; surveys; distance indicators
COSMOS2020: Identification of High-z Protocluster Candidates in COSMOS

We conduct a systematic search for protocluster candidates at z ≥ 6 in the Cosmic Evolution Survey (COSMOS) field using the recently released COSMOS2020 source catalog. We select galaxies using a number of selection criteria to obtain a sample of galaxies that have a high probability of being inside a given redshift bin. We then apply overdensity analysis to the bins using two density estimators, a Weighted Adaptive Kernel estimator and a Weighted Voronoi Tessellation estimator. We have found 15 significant (>4σ) candidate galaxy overdensities across the redshift range 6 ≤ z ≤ 7.7. The majority of the galaxies appear to be on the galaxy main sequence at their respective epochs. We use multiple stellar-mass-to-halo-mass conversion methods to obtain a range of dark matter halo mass estimates for the overdensities in the range of ~1011-1013 M ⊙, at the respective redshifts of the overdensities. The number and the masses of the halos associated with our protocluster candidates are consistent with what is expected from the area of a COSMOS-like survey in a standard Λ cold dark matter cosmology. Through comparison with simulation, we expect that all of the overdensities at z ≃ 6 will evolve into Virgo-/Coma-like clusters at present (i.e., with masses ~1014-1015 M ⊙). Compared to other overdensities identified at z ≥ 6 via narrowband selection techniques, the overdensities presented appear to have ~10× higher stellar masses and star formation rates (SFRs). We compare the evolution in the total SFR and stellar mass content of the protocluster candidates across the redshift range 6 ≤ z ≤ 7.7 and find agreement with the total average SFR from simulations.

Keywords: high-redshift galaxy clusters; galaxy evolution; large-scale structure of the universe
Planetesimal Formation by the Gravitational Instability of Dust Ring Structures

We investigate the gravitational instability (GI) of dust ring structures and the formation of planetesimals by their gravitational collapse. The normalized dispersion relation of a self-gravitating ring structure includes two parameters that are related to its width and line mass (the mass per unit length). We survey these parameters and calculate the growth rate and wavenumber. Additionally, we investigate the formation of planetesimals by growth of the GI of the ring that is formed by the growth of the secular GI of the protoplanetary disk. We adopt a massive, dust-rich disk as a disk model. We find the range of radii for fragmentation by the ring GI as a function of the width of the ring. The innermost radius for the ring GI is smaller for a smaller ring width. We also determine the range of the initial planetesimal mass resulting from the fragmentation of the ring GI. Our results indicate that the planetesimal mass can be as large as 1028 g at its birth after the fragmentation. It can be as low as about 1025 g if the ring width is 0.1% of the ring radius, and the lower limit increases with the ring width. Furthermore, we obtain approximate formulae for the upper and lower limits of the planetesimal mass. We predict that the planetesimals formed by the ring GI have prograde rotations because of the Coriolis force acting on the contracting dust. This is consistent with the fact that many trans-Neptunian binaries exhibit prograde rotation.

Keywords: gravitational instability; protoplanetary disks; planet formation; planetesimals
A Unified Model for Bipolar Outflows from Young Stars: Kinematic and Mixing Structures in HH 30

The young stellar source HH 30 is a textbook example of an ionic optical jet originating from a disk in an edge-on system shown by the Hubble Space Telescope. It has a remnant envelope in 12CO observed by the Atacama Large Millimeter/submillimeter Array. The optical jet is characterized by its narrow appearance, large line width at the base, and high temperature inferred from line diagnostics. Three featured structures can be identified, most evident in the transverse position–velocity diagrams: an extremely-high-velocity wide-angle wind component with large spectral widths in the optical, a very-low-velocity ambient surrounding medium seen in 12CO, and a low-velocity region traced by 12CO nested both in velocity and location between the primary wind and ambient environment. A layered cavity with multiple shells forms nested morphological and kinematic structures around the optical jet. The atomic gas originating from the innermost region of the disk attains a sufficient temperature and ionization to emit brightly in forbidden lines as an optical jet. The wide-angle portion expands, forming a low-density cavity. The filamentary 12CO encompassing the wind cavity is mixed and advected inward through the action of the magnetic interplay of the wide-angle wind with the molecular ambient medium. The magnetic interplay results in the layered shells penetrating deeply into the vast cavity of tenuous atomic wind material. The HH 30 system is an ideal manifestation of the unified wind model of Shang et al. (2020, 2023), with clearly distinguishable atomic and molecular species mixed through the atomic lightly ionized magnetized wind and the surrounding cold molecular ambient material.

Keywords: stellar jets; stellar winds; stellar wind bubbles; collapsing clouds; young stellar objects; protostars; star formation; interstellar line emission; co line emission; herbig-haro objects; emission nebulae; hubble space telescope
Earth as an Exoplanet. II. Earth's Time-variable Thermal Emission and Its Atmospheric Seasonality of Bioindicators

We assess the dependence of Earth's disk-integrated mid-infrared thermal emission spectrum on observation geometries and investigate which and how spectral features are impacted by seasonality on Earth. We compiled an exclusive data set containing 2690 disk-integrated thermal emission spectra for four different full-disk observing geometries (North and South Pole-centered and Africa and Pacific-centered equatorial views) over four consecutive years. The spectra were derived from 2378 spectral channels in the wavelength range from 3.75-15.4 μm (nominal resolution ≈1200) and were recorded by the Atmospheric Infrared Sounder on board the Aqua satellite. We learned that there is significant seasonal variability in Earth's thermal emission spectrum, and the strength of spectral features of bioindicators, such as N2O, CH4, O3, and CO2 depends strongly on both season and viewing geometry. In addition, we found a strong spectral degeneracy with respect to the latter two indicating that multi-epoch measurements and time-dependent signals may be required in order to fully characterize planetary environments. Even for Earth and especially for equatorial views, the variations in flux and strength of absorption features in the disk-integrated data are small and typically ≤ 10%. Disentangling these variations from the noise in future exoplanet observations will be a challenge. However, irrespectively of when the planet will be measured (i.e., day or night or season) the results from mid-infrared observations will remain the same to the zeroth order, which is an advantage over reflected light observations.

Keywords: astrobiology; earth (planet); infrared spectroscopy; biosignatures; exoplanet atmospheric variability; space vehicle instruments
Measuring the Dust Masses of Protoplanetary Disks in Lupus with ALMA: Evidence That Disks Can Be Optically Thick at 3 mm

Accurate disk mass measurements are necessary to constrain disk evolution and the timescale of planet formation, but such measurements are difficult to make and are very dependent on assumptions. Here, we look at the assumption that the disk is optically thin at radio wavelengths and the effect of this assumption on measurements of disk dust mass. We model the optical to radio spectral energy distributions of 41 protoplanetary disks located in the young (~1-3 Myr old) Lupus star-forming region, including 0.89 1.33 and 3 mm flux densities when available. We measure disk dust masses that are ~1.5-6 times higher than when using the commonly adopted disk dust mass equation under the assumption of optically thin emission in the (sub)millimeter range. The cause of this discrepancy is that most disks are optically thick at millimeter wavelengths, even up to 3 mm, demonstrating that observations at longer wavelengths are needed to trace the fully optically thin emission of disks.

Keywords: protoplanetary disks; t tauri stars; neural networks
Modeling Stellar Ca II H and K Emission Variations: Spot Contribution to the S-index

The S-index is a measure of emission in the Ca II H and K lines and is a widely used proxy of stellar magnetic activity. It has been assumed until now that the S-index is mainly affected by bright plage regions in the chromosphere. In particular, the effect of starspots on the S-index has been neglected. In this study, we revisit this assumption. For this, we analyze high-resolution observations of sunspots recorded in the Ca II H spectral line at the Swedish 1 m Solar Telescope and determine the contrast of spots with respect to the quiet surroundings. We find that the Ca II H line core averaged over whole sunspots (including superpenumbrae) is brighter than in the quiet surroundings and that the spot contrast in the line core is comparable to the facular contrast. This allows us to get a first estimate of the influence of spots on the S-index. We show that spots increase the S-index. While this increase is quite small for the Sun, it becomes significantly larger for more active stars. Further, we show that the inclusion of the contribution of spots to the S-index strongly affects the relationship between the S-index and stellar disk area coverages by spots and faculae, and present the new relations.

Keywords: stellar activity; stellar chromospheres; starspots; sunspots; plages
Photometric Objects Around Cosmic Webs (PAC). VI. High Satellite Fraction of Quasars

The Photometric objects Around Cosmic webs (PAC) approach developed in Xu et al. has the advantage of making full use of spectroscopic and deeper photometric surveys. With the merits of PAC, the excess surface density ${\bar{n}}_{2}{w}_{{\rm{p}}}$ of neighboring galaxies can be measured down to stellar mass 1010.80 M ⊙ around quasars at redshift 0.8 < z s < 1.0, with the data from the Sloan Digital Sky Survey IV extended Baryon Oscillation Spectroscopic Survey and the Dark Energy Spectroscopic Instrument Legacy Imaging Surveys. We find that ${\bar{n}}_{2}{w}_{{\rm{p}}}$ generally increases quite steeply with the decrease of the separation. Using the subhalo abundance-matching method, we can accurately model the ${\bar{n}}_{2}{w}_{{\rm{p}}}$ both on small and large scales. We show that the steep increase of ${\bar{n}}_{2}{w}_{{\rm{p}}}$ toward the quasars requires that a large fraction ${f}_{\mathrm{sate}}={0.29}_{-0.06}^{+0.05}$ of quasars should be satellites in massive halos, and we find that this fraction measurement is insensitive to the assumptions of our modeling. This high satellite fraction indicates that the subhalos have nearly the same probability of hosting quasars as the halos for the same (infall) halo mass and that the large-scale environment has negligible effect on the quasar activity. We show that even with this high satellite fraction, each massive halo on average does not host more than one satellite quasar, due to the sparsity of quasars.

Keywords: agn host galaxies; stellar mass functions; quasars; active galaxies