adsabs/SciX_UAT_keywords huggingface dataset:
GaiaHub: A Method for Combining Data from the Gaia and Hubble Space Telescopes to Derive Improved Proper Motions for Faint Stars

We present GAIAHUB, a publicly available tool that combines Gaia measurements with Hubble Space Telescope (HST) archival images to derive proper motions (PMs). It increases the scientific impact of both observatories beyond their individual capabilities. Gaia provides PMs across the whole sky, but the limited mirror size and time baseline restrict the best PM performance to relatively bright stars. HST can measure accurate PMs for much fainter stars over a small field, but this requires two epochs of observation, which are not always available. GAIAHUB yields considerably improved PM accuracy compared to Gaia-only measurements, especially for faint sources (G ≳ 18), requiring only a single epoch of HST data observed more than ~7 yr ago (before 2012). This provides considerable scientific value, especially for dynamical studies of stellar systems or structures in and beyond the Milky Way (MW) halo, for which the member stars are generally faint. To illustrate the capabilities and demonstrate the accuracy of GAIAHUB, we apply it to samples of MW globular clusters (GCs) and classical dwarf spheroidal (dSph) satellite galaxies. This allows us, e.g., to measure the velocity dispersions in the plane of the sky for objects out to and beyond ~100 kpc. We find, on average, mild radial velocity anisotropy in GCs, consistent with existing results for more nearby samples. We observe a correlation between the internal kinematics of the clusters and their ellipticity, with more isotropic clusters being, on average, more round. Our results also support previous findings that Draco and Sculptor dSph galaxies appear to be radially anisotropic systems.

Keywords: proper motions; stellar kinematics; globular star clusters; dwarf galaxies
Theoretical versus Observational Uncertainties: Composition of Giant Exoplanets

In order to characterize giant exoplanets and better understand their origin, knowledge of how the planet's composition depends on its mass and stellar environment is required. In this work, we simulate the thermal evolution of gaseous planets and explore how various common model assumptions such as different equations of state, opacities, and heavy-element distributions affect the inferred radius and metallicity. We examine how the theoretical uncertainties translate into uncertainties in the inferred planetary radius and bulk metallicity. While we confirm the mass-metallicity trend previously reported in the literature, this correlation disappears when removing a 20 M⊕ heavy-element core from all the planets. We also show that using an updated hydrogen-helium equation of state leads to more compact planets. As a result, we present six planets that should be classified as inflated warm Jupiters. We next demonstrate that including the opacity enhancement due to metal-rich envelopes of irradiated planets changes the planetary radius significantly, which can have large effects on the inferred metallicity. Even though there are other model assumptions that have not been considered in this work, we could show that the calculated theoretical uncertainties can already be comparable or even larger than the observational ones. Therefore, theoretical uncertainties are likely to be even larger. We therefore conclude that progress in theoretical models of giant planets is essential in order to take full advantage of current and future exoplanetary data.

Keywords: planetary interior; exoplanet evolution; extrasolar gaseous giant planets; exoplanets
Observing Atmospheric Escape in Sub-Jovian Worlds with JWST

Hydrodynamic atmospheric escape is considered an important process that shapes the evolution of sub-Jovian exoplanets, particularly those with short orbital periods. The metastable He line in the near-infrared at 1.083 μm is a reliable tracer of atmospheric escape in hot exoplanets, with the advantage of being observable from the ground. However, observing escaping He in sub-Jovian planets has remained challenging due to the systematic effects and telluric contamination present in ground-based data. With the successful launch and operations of JWST, we now have access to extremely stable high-precision near-infrared spectrographs in space. Here we predict the observability of metastable He with JWST in two representative and previously well-studied warm Neptunes, GJ 436 b (T eq = 687 K, R p = 0.37 R J) and GJ 1214 b (T eq = 588 K, R p = 0.25 R J). Our simulated JWST observations for GJ 436 b demonstrate that a single transit with NIRSpec/G140H is sensitive to mass-loss rates that are two orders of magnitude lower than what is detectable from the ground. Our exercise for GJ 1214 b show that the best configuration to observe the relatively weak outflows of warm Neptunes with JWST is with NIRSpec/G140H, and that NIRSpec/G140M and NIRISS/SOSS are less optimal. Since none of these instrument configurations can spectrally resolve the planetary absorption, we conclude that the 1D isothermal Parker-wind approximation may not be sufficient for interpreting such observations. More sophisticated models are critical for breaking the degeneracy between outflow temperature and mass-loss rate for JWST measurements of metastable He.

Keywords: exoplanet atmospheres; extrasolar gaseous planets; planet hosting stars; infrared astronomy
Oblique Tearing Mode Instability: Guide Field and Hall Effect

The tearing mode instability is one important mechanism that may explain the triggering of fast magnetic reconnection in astrophysical plasmas, such as the solar corona and the Earth's magnetosphere. In this paper, the linear stability analysis of the tearing mode is carried out for a current sheet in the presence of a guide field, including the Hall effect. We show that the presence of a strong guide field does not modify the most unstable mode in the 2D wavevector space orthogonal to the current gradient direction, which remains the fastest-growing parallel mode. With the Hall effect, the inclusion of a guide field turns the nondispersive propagation along the guide field direction to a dispersive one. The oblique modes have a wavelike structure along the normal direction of the current sheet and a strong guide field suppresses this structure while making the eigenfunctions asymmetric.

Keywords: solar magnetic reconnection; plasma physics; magnetohydrodynamics
Role of the Fan Beam Model in Population Synthesis of Isolated Radio Pulsars

On the basis of the PSRPOPPY software package, we developed an evolution model of population synthesis for isolated radio pulsars by incorporating the fan beam model, an alternative radio emission beam model to the widely used conal beam model. With proper choice of related models and parameters, we successfully reproduced the observational distributions of Galactic longitude (l) and latitude (b), spin period, period derivative, dispersion measure and 1.4 GHz flux density for the 1214 isolated pulsars discovered by the Parkes multibeam and Swinburne pulsar surveys. The size of the underlying population of radio-loud pulsars is found to be 2.27 × 106, which is larger than the underlying population of radio-loud pulsars simulated with the conal beam model. The model is used to estimate the number of isolated radio pulsars detected by the Galactic-plane pulsar survey with Five hundred-meter Aperture Spherical Telescope (FAST). Approximately 2700 and 240 new isolated pulsars are expected to be discovered in the inner galactic plane (20° < l < 90°, ∣b∣ < 10°) and the outer galactic plane (150° < l < 210°, ∣b∣ < 10°), respectively. These numbers are smaller than those estimated by the evolution models with conal beams and the snapshot models.

Keywords: radio pulsars
Distinguishing Binary Neutron Star from Neutron Star-Black Hole Mergers with Gravitational Waves

The gravitational-wave signal from the merger of two neutron stars cannot be easily differentiated from the signal produced by a comparable-mass mixed binary of a neutron star and a black hole. Indeed, both binary types can account for the gravitational-wave signal GW170817 even if its electromagnetic counterpart emission is taken into account. We propose a method that requires neither information from the post-inspiral phase of the binary nor an electromagnetic counterpart to identify mixed binaries of neutron stars merging with low-mass black holes using gravitational waves alone. This method is based on the fact that certain neutron star properties that can be measured with gravitational waves are common or similar for all neutron stars. For example all neutron stars share the same equation of state, and if the latter is hadronic, neutron stars have similar radii. If a mixed binary is misidentified as a neutron star binary, the inferred neutron star properties will be misestimated and appear as outliers in a population of low-mass binaries. We show that as few as ∼5 low-mass events will allow for the identification of the type of one event at the 80% confidence level. We model the population of low-mass binaries with a hierarchical mixture model and show that we can constrain the existence of mixed binaries or measure their abundance relative to neutron star binaries to ∼0.1 at the 68% credible level with 100 events.

Keywords: gravitational waves; neutron stars; nuclear astrophysics
Dusty Starbursts Masquerading as Ultra-high Redshift Galaxies in JWST CEERS Observations

Lyman-break galaxy (LBG) candidates at z ≳ 10 are rapidly being identified in James Webb Space Telescope (JWST)/NIRCam observations. Due to the (redshifted) break produced by neutral hydrogen absorption of rest-frame UV photons, these sources are expected to drop out in the bluer filters while being well detected in redder filters. However, here we show that dust-enshrouded star-forming galaxies at lower redshifts (z ≲ 7) may also mimic the near-infrared (near-IR) colors of z > 10 LBGs, representing potential contaminants in LBG candidate samples. First, we analyze CEERS-DSFG-1, a NIRCam dropout undetected in the F115W and F150W filters but detected at longer wavelengths. Combining the JWST data with (sub)millimeter constraints, including deep NOEMA interferometric observations, we show that this source is a dusty star-forming galaxy (DSFG) at z ≈ 5.1. We also present a tentative 2.6σ SCUBA-2 detection at 850 μm around a recently identified z ≈ 16 LBG candidate in the same field and show that, if the emission is real and associated with this candidate, the available photometry is consistent with a z ~ 5 dusty galaxy with strong nebular emission lines despite its blue near-IR colors. Further observations on this candidate are imperative to mitigate the low confidence of this tentative submillimeter emission and its positional uncertainty. Our analysis shows that robust (sub)millimeter detections of NIRCam dropout galaxies likely imply z ~ 4-6 redshift solutions, where the observed near-IR break would be the result of a strong rest-frame optical Balmer break combined with high dust attenuation and strong nebular line emission, rather than the rest-frame UV Lyman break. This provides evidence that DSFGs may contaminate searches for ultra-high redshift LBG candidates from JWST observations.

Keywords: high-redshift galaxies; galaxies; lyman-break galaxies; galaxy photometry; submillimeter astronomy; millimeter astronomy; luminous infrared galaxies; starburst galaxies; james webb space telescope; near infrared astronomy; dust continuum emission; emission line galaxies
NOEMA Detection of Circumnuclear Molecular Gas in X-Ray Weak Dual Active Galactic Nuclei: No Evidence for Heavy Obscuration

Dual active galactic nuclei (AGNs), which are the manifestation of two actively accreting supermassive black holes (SMBHs) hosted by a pair of merging galaxies, are a unique laboratory for studying the physics of SMBH feeding and feedback during an indispensable stage of galaxy evolution. In this work, we present NOEMA CO(2-1) observations of seven kiloparsec-scale dual-AGN candidates drawn from a recent Chandra survey of low redshift, optically classified AGN pairs. These systems are selected because they show unexpectedly low 2-10 keV X-ray luminosities for their small physical separations signifying an intermediate-to-late stage of merger. Circumnuclear molecular gas traced by the CO(2-1) emission is significantly detected in six of the seven pairs and 10 of the 14 nuclei, with an estimated mass ranging between (0.2-21) × 109 M ⊙. The primary nuclei, i.e., the ones with the higher stellar velocity dispersion, tend to have a higher molecular gas mass than the secondary. Most CO-detected nuclei show a compact morphology, with a velocity field consistent with a kiloparsec-scale rotating structure. The inferred hydrogen column densities range between 5 × 1021-2 × 1023 cm-2, but mostly at a few times 1022 cm-2, in broad agreement with those derived from X-ray spectral analysis. Together with the relatively weak mid-infrared emission, the moderate column density argues against the prevalence of heavily obscured, intrinsically luminous AGNs in these seven systems, but favors a feedback scenario in which AGN activity triggered by a recent pericentric passage of the galaxy pair can expel circumnuclear gas and suppress further SMBH accretion.

Keywords: active galaxies; interacting galaxies; active galactic nuclei; submillimeter astronomy; interferometry; co line emission; galaxy mergers
All the PAHs: An AKARI-Spitzer Cross-archival Spectroscopic Survey of Aromatic Emission in Galaxies

We present a large sample of 2.5-38 μm galaxy spectra drawn from a cross-archival comparison in the AKARI-Spitzer Extragalactic Spectral Survey, and investigate a subset of 113 star-forming galaxies with prominent polycyclic aromatic hydrocarbon (PAH) emission spanning a wide range of star formation properties. With AKARI's extended 2.5-5 μm wavelength coverage, we self-consistently model for the first time all PAH emission bands using a modified version of PAHFIT. We find LPAH 3.3/LIR ∼ 0.1%, and the 3.3 μm PAH feature contributes ∼1.5%-3% to the total PAH power—somewhat less than earlier dust models have assumed. We establish a calibration between 3.3 μm PAH emission and star formation rate, but also find regimes where it loses reliability, including at high luminosity and low metallicity. The 3.4 μm aliphatic emission and a broad plateau feature centered at 3.47 μm are also modeled. As the PAH feature with the shortest wavelength, the one at 3.3 μm is susceptible to attenuation, leading to differences of a factor of ∼3 in the inferred star formation rate at high obscuration with different assumed attenuation geometries. Surprisingly, LPAH 3.3/LΣ PAH shows no sign of decline at high luminosities, and the low-metallicity dwarf galaxy II Zw 40 exhibits an unusually strong 3.3 μm band; both results suggest either that the smallest PAHs are better able to survive under intense radiation fields than presumed, or that PAH emission is shifted to shorter wavelengths in intense and high-energy radiation environments. A photometric surrogate for 3.3 μm PAH luminosity using JWST/NIRCam is provided and found to be highly reliable at low redshift.

Keywords: polycyclic aromatic hydrocarbons; interstellar dust extinction; starburst galaxies; luminous infrared galaxies; ultraluminous infrared galaxies
Distribution and Properties of Molecular Gas toward the Monoceros OB1 Region

We perform a comprehensive CO study toward the Monoceros OB1 (Mon OB1) region based on the Milky Way Imaging Scroll Painting survey at an angular resolution of about 50″. The high-sensitivity data, together with the high dynamic range, show that molecular gas in the 8° × 4° region displays complicated hierarchical structures and various morphology (e.g., filamentary, cavity-like, shell-like, and other irregular structures). Based on Gaussian decomposition and clustering for 13CO data, a total of 263 13CO structures are identified in the whole region, and 88% of raw data flux is recovered. The dense gas with relatively high column density from the integrated CO emission is mainly concentrated in the region where multiple 13CO structures are overlapped. Combining the results of 32 large 13CO structures with distances from Gaia DR3, we estimate an average distance of ${729}_{-45}^{+45}\,\mathrm{pc}$ for the giant molecular cloud (GMC) complex. The total mass of the GMC complex traced by 12CO, 13CO, and C18O is 1.1 × 105 M ⊙, 4.3 × 104 M ⊙, and 8.4 × 103 M ⊙, respectively. The dense gas fraction shows a clear difference between Mon OB1 GMC East (12.4%) and Mon OB1 GMC West (3.3%). Our results show that the dense gas environment is closely linked to the nearby star-forming regions. On the other hand, star-forming activities have a great influence on the physical properties of the surrounding molecular gas (larger velocity dispersion, higher temperatures, more complex velocity structures, etc.). We also discuss the distribution/kinematics of molecular gas associated with nearby star-forming activities.

Keywords: distance measure; interstellar medium; molecular clouds; stellar feedback
Approximating Density Probability Distribution Functions Across Cosmologies

Using a suite of self-similar cosmological simulations, we measure the probability distribution functions (PDFs) of real-space density, redshift-space density, and their geometric mean. We find that the real-space density PDF is well-described by a function of two parameters: n s , the spectral slope, and σ L , the linear rms density fluctuation. For redshift-space density and the geometric mean of real- and redshift-space densities, we introduce a third parameter, ${s}_{L}=\sqrt{\langle {\left({{dv}}_{\mathrm{pec}}^{L}/{dr}\right)}^{2}\rangle }/H$ . We find that density PDFs for the LCDM cosmology is also well-parameterized by these three parameters. As a result, we are able to use a suite of self-similar cosmological simulations to approximate density PDFs for a range of cosmologies. We make the density PDFs publicly available and provide an analytical fitting formula for them.

Keywords: cosmology; cosmological evolution; hierarchical cosmology; large-scale structure of the universe; redshifted; cosmological parameters; cosmological models; dark matter; bianchi cosmology; n-body simulations
Asymmetric Nuclear Matter in Relativistic Mean-field Models with Isoscalar- and Isovector-meson Mixing

Using the relativistic mean-field model with nonlinear couplings between the isoscalar and isovector mesons, we study the properties of isospin-asymmetric nuclear matter. Not only the vector mixing, ω μ ω μ ρ ν ρ ν , but also the quartic interaction due to the scalar mesons, σ 2 δ 2, is taken into account to investigate the density dependence of nuclear symmetry energy, E sym, and the neutron star properties. It is found that the δ meson increases E sym at high densities, whereas the σ-δ mixing makes E sym soft above the saturation density. Furthermore, the δ meson and its mixing have a large influence on the radius and tidal deformability of a neutron star. In particular, the σ-δ mixing reduces the neutron star radius; thus, the present calculation can simultaneously reproduce the dimensionless tidal deformabilities of a canonical 1.4 M ⊙ neutron star observed from the binary neutron star merger GW170817 and the compact binary coalescence GW190814.

Keywords: neutron stars; relativistic mechanics; nuclear physics; gravitational waves
JWST/NIRCam Detection of the Fomalhaut C Debris Disk in Scattered Light

Observations of debris disks offer important insights into the formation and evolution of planetary systems. Though M dwarfs make up approximately 80% of nearby stars, very few M dwarf debris disks have been studied in detail—making it unclear how or if the information gleaned from studying debris disks around more massive stars extends to the more abundant M dwarf systems. We report the first scattered-light detection of the debris disk around the M4 star Fomalhaut C using JWST's Near Infrared Camera (NIRCam; 3.6 and 4.4 μm). This result adds to the prior sample of only four M dwarf debris disks with detections in scattered light and marks the latest spectral type and oldest star among them. The size and orientation of the disk in these data are generally consistent with the prior Atacama Large Millimeter/submillimeter Array submillimeter detection. Though no companions are identified, these data provide strong constraints on their presence—with sensitivity sufficient to recover sub-Saturn mass objects in the vicinity of the disk. This result illustrates the unique capability of JWST to uncover elusive M dwarf debris disks in scattered light and lays the groundwork for deeper studies of such objects in the 2–5 μm regime.

Keywords: debris disks; m dwarf stars; coronagraphic imaging; direct imaging; high contrast techniques
Following Up the Kepler Field: Masses of Targets for Transit Timing and Atmospheric Characterization

We identify a set of planetary systems observed by Kepler that merit transit-timing variation (TTV) analysis given the orbital periods of transiting planets, the uncertainties for their transit times, and the number of transits observed during the Kepler mission. We confirm the planetary nature of four Kepler Objects of Interest within multicandidate systems. We forward-model each of the planetary systems identified to determine which systems are likely to yield mass constraints that may be significantly improved upon with follow-up transit observations. We find projected TTVs diverge by more than 90 minutes after 6000 days in 27 systems, including 22 planets with orbital periods exceeding 25 days. Such targets would benefit the most from additional transit-timing data. TTV follow-up could push exoplanet characterization to lower masses, at greater orbital periods and at cooler equilibrium temperatures than is currently possible from the Kepler data set alone. Combining TTVs and recently revised stellar parameters, we characterize an ensemble of homogeneously selected planets and identify planets in the Kepler field with large-enough estimated transmission annuli for atmospheric characterization with James Webb Space Telescope.

Keywords: transit timing variation method; exoplanet systems
Polarization Properties of the Weakly Magnetized Neutron Star X-Ray Binary GS 1826-238 in the High Soft State

The launch of the Imaging X-ray Polarimetry Explorer (IXPE) on 2021 December 9 has opened a new window in X-ray astronomy. We report here the results of the first IXPE observation of a weakly magnetized neutron star, GS 1826-238, performed on 2022 March 29-31 when the source was in a high soft state. An upper limit (99.73% confidence level) of 1.3% for the linear polarization degree is obtained over the IXPE 2-8 keV energy range. Coordinated INTEGRAL and NICER observations were carried out simultaneously with IXPE. The spectral parameters obtained from the fits to the broadband spectrum were used as inputs for Monte Carlo simulations considering different possible geometries of the X-ray emitting region. Comparing the IXPE upper limit with these simulations, we can put constraints on the geometry and inclination angle of GS 1826-238.

Keywords: low-mass x-ray binary stars; x-ray astronomy; x-ray binary stars