adsabs/SciX_UAT_keywords huggingface dataset:
Radio Emission from High-redshift Active Galactic Nuclei in the JADES and CEERS Surveys

Recent calculations indicate that radio emission from quasars at z ∼ 6–7 could be detected at much earlier stages of evolution, at z ∼ 14–15, by the Next-Generation Very Large Array (ngVLA) and the Square Kilometer Array (SKA). However, the James Webb Space Telescope has now discovered less luminous active galactic nuclei (AGNs) at z > 4 and a few massive black holes (BHs) at z > 10, which may be the progenitors of supermassive black holes (SMBHs) but at different stages of growth. Radio detections of these new AGNs would provide complementary measures of their properties and those of their host galaxies. Here we estimate radio flux densities for 19 new AGNs found by the JADES, CEERS, and UNCOVER surveys. We find that ngVLA should be able to detect most of these sources in targeted surveys with integration times of 10–100 hr (and in just 1 hr for a few of them) but most would require at least 100 hr of SKA time in spite of its greater sensitivities at low frequencies. In some cases, radio emission from the BH can be distinguished from that of H II regions and supernovae in their host galaxies, which could be used to estimate their star formation rates. Such detections would be yet another example of the useful synergies between near-infrared and radio telescopes in SMBH science in the coming decade.

Keywords: low-luminosity active galactic nuclei; early universe; high-redshift galaxies
Deciphering the Morphological Origins of X-shaped Radio Galaxies: Numerical Modeling of Backflow versus Jet Reorientation

X-shaped radio galaxies (XRGs) develop when certain extragalactic jets deviate from their propagation path. An asymmetric ambient medium (backflow model) or complex active galactic nucleus activity (jet-reorientation model) enforcing the jet direction to deviate may cause these structures. In this context, the present investigation focuses on the modeling of XRGs by performing 3D relativistic magnetohydrodynamic simulations. We implement different jet-propagation models applying an initially identical jet-ambient medium configuration to understand distinctive features. This study, the first of its kind, demonstrates that all adopted models produce XRGs with notable properties, thereby challenging the notion of a universal model. Jet reorientation naturally explains several contentious properties of XRGs, including wing alignment along the ambient medium's primary axis, development of collimated lobes, and the formation of noticeably longer wings than active lobes. These XRGs disrupt the cluster medium by generating isotropic shocks and channeling more energy than in the backflow scenario. Our synthetic thermal X-ray maps of the cluster medium reveal four clear elongated cavities associated with the wing-lobe alignment, regardless of projection effects, but they affect their age estimation. We show that the depth and geometric alignment of the evolved cavities may qualify as promising characteristics of XRGs, which may be used to disentangle different formation scenarios.

Keywords: shocks; magnetohydrodynamical simulations; x-ray sources; galaxy clusters; relativistic jets
ZTF20aajnksq (AT 2020blt): A Fast Optical Transient at z ≈ 2.9 with No Detected Gamma-Ray Burst Counterpart

We present ZTF20aajnksq (AT 2020blt), a fast-fading (Δr = 2.3 mag in Δt = 1.3 days) red (g - r ≈ 0.6 mag) and luminous (M1626 Å = -25.9 mag) optical transient at z = 2.9 discovered by the Zwicky Transient Facility (ZTF). AT 2020blt shares several features in common with afterglows to long-duration gamma-ray bursts (GRBs): (1) an optical light curve well-described by a broken power law with a break at tj = 1 d (observer frame); (2) a luminous (L0.3-10 KeV = 1046 erg s-1) X-ray counterpart; and (3) luminous (L10 GHz = 4 × 1031 erg s-1 Hz-1) radio emission. However, no GRB was detected in the 0.74 days between the last ZTF nondetection (r > 21.36 mag) and the first ZTF detection (r = 19.60 mag), with an upper limit on the isotropic-equivalent gamma-ray energy release of Eγ,iso < 7 × 1052 erg. AT 2020blt is thus the third afterglow-like transient discovered without a detected GRB counterpart (after PTF11agg and ZTF19abvizsw) and the second (after ZTF19abvizsw) with a redshift measurement. We conclude that the properties of AT 2020blt are consistent with a classical (initial Lorentz factor Γ0 ≳ 100) on-axis GRB that was missed by high-energy satellites. Furthermore, by estimating the rate of transients with light curves similar to that of AT 2020blt in ZTF high-cadence data, we agree with previous results that there is no evidence for an afterglow-like phenomenon that is significantly more common than classical GRBs, such as dirty fireballs. We conclude by discussing the status and future of fast-transient searches in wide-field high-cadence optical surveys.

Keywords: gamma-ray bursts; radio transient sources; transient sources; x-ray transient sources; sky surveys; surveys
Investigating Global Convective Dynamos with Mean-field Models: Full Spectrum of Turbulent Effects Required

The role of turbulent effects for dynamos in the Sun and stars continues to be debated. Mean-field (MF) theory provides a broadly used framework to connect these effects to fundamental magnetohydrodynamics. While inaccessible observationally, turbulent effects can be directly studied using global convective dynamo (GCD) simulations. We measure the turbulent effects in terms of turbulent transport coefficients, based on the MF framework, from an exemplary GCD simulation using the test-field method. These coefficients are then used as an input into an MF model. We find a good agreement between the MF and GCD solutions, which validates our theoretical approach. This agreement requires all turbulent effects to be included, even those which have been regarded as unimportant so far. Our results suggest that simple dynamo models, as are commonly used in the solar and stellar community, relying on very few, precisely fine-tuned turbulent effects, may not be representative of the full dynamics of dynamos in global convective simulations and astronomical objects.

Keywords: magnetohydrodynamics; solar dynamo; solar cycle; stellar activity; stellar magnetic fields
Particle Acceleration in Magnetic Reconnection with Ad Hoc Pitch-angle Scattering

Particle acceleration during magnetic reconnection is a long-standing topic in space, solar, and astrophysical plasmas. Recent 3D particle-in-cell simulations of magnetic reconnection show that particles can leave flux ropes due to 3D field-line chaos, allowing particles to access additional acceleration sites, gain more energy through Fermi acceleration, and develop a power-law energy distribution. This 3D effect does not exist in traditional 2D simulations, where particles are artificially confined to magnetic islands due to their restricted motions across field lines. Full 3D simulations, however, are prohibitively expensive for most studies. Here, we attempt to reproduce 3D results in 2D simulations by introducing ad hoc pitch-angle scattering to a small fraction of the particles. We show that scattered particles are able to transport out of 2D islands and achieve more efficient Fermi acceleration, leading to a significant increase of energetic particle flux. We also study how the scattering frequency influences the nonthermal particle spectra. This study helps achieve a complete picture of particle acceleration in magnetic reconnection.

Keywords: plasma astrophysics; solar flares; solar corona; solar magnetic reconnection; space plasmas; relativistic jets; pulsar wind nebulae
The Abundance of Chlorine in the Atmosphere of HD 87240

High resolution high signal-to-noise UVES spectra of the late B-type chemically peculiar star, HD 87240, a member of the NGC 3114 open cluster, have been synthesized to measure the abundance of chlorine, an element which is rarely found in late B-type stars. Sixteen lines of Cl II are found and the mean chlorine overabundance is about 2.1 dex higher than the solar abundance, which is slightly lower than the chlorine excess in HR 1094, another chlorine-rich late B-type star.

Keywords: chemically peculiar stars
Measuring HERA's Primary Beam in Situ: Methodology and First Results

The central challenge in 21 cm cosmology is isolating the cosmological signal from bright foregrounds. Many separation techniques rely on the accurate knowledge of the sky and the instrumental response, including the antenna primary beam. For drift-scan telescopes, such as the Hydrogen Epoch of Reionization Array (HERA), that do not move, primary beam characterization is particularly challenging because standard beam-calibration routines do not apply (Cornwell et al.) and current techniques require accurate source catalogs at the telescope resolution. We present an extension of the method from Pober et al. where they use beam symmetries to create a network of overlapping source tracks that break the degeneracy between source flux density and beam response and allow their simultaneous estimation. We fit the beam response of our instrument using early HERA observations and find that our results agree well with electromagnetic simulations down to a -20 dB level in power relative to peak gain for sources with high signal-to-noise ratio. In addition, we construct a source catalog with 90 sources down to a flux density of 1.4 Jy at 151 MHz.

Keywords: radio astronomy; h i line emission; cosmology
Characterization of the Atmosphere of Super-Earth 55 Cancri e Using High-resolution Ground-based Spectroscopy

The nearby super-Earth 55 Cnc e orbits a bright (V = 5.95 mag) star with a period of ∼18 hr and a mass of ∼8M⊕. Its atmosphere may be water-rich and have a large-scale height; though, attempts to characterize it have yielded ambiguous results. Here we present a sensitive search for water and TiO in its atmosphere at high spectral resolution using the Gemini North telescope and the GRACES spectrograph. We combine observations with previous observations from Subaru and CFHT, improving the constraints on the presence of water vapor. We adopt parametric models with an updated planet radius based on recent measurements, and use a cross-correlation technique to maximize sensitivity. Our results are consistent with atmospheres that are cloudy or contain minimal amounts of water and TiO. Using these parametric models, we rule out a water-rich atmosphere (VMR $\geqslant $ 0.1%) with a mean molecular weight of $\leqslant $ 15 g mol-1 at a 3σ confidence level, improving on the previous limit by a significant margin. For TiO, we rule out a mean molecular weight of $\leqslant $ 5 g mol-1 with a 3σ confidence level for a VMR greater than 10-8; for a VMR of greater than 10-7, the limit rises to a mean molecular weight of $\leqslant $ 10 g mol-1. We can rule out low mean-molecular-weight chemical equilibrium models both including and excluding TiO/VO at very high confidence levels (>10σ). Overall, our results are consistent with an atmosphere with a high mean molecular weight and/or clouds, or no atmosphere.

Keywords: high resolution spectroscopy; exoplanet atmospheric composition; transits; super earths; ground-based astronomy; optical astronomy
Solar Origin of Compressive Alfvénic Spikes/Kinks as Observed by Parker Solar Probe

The solar wind is found by the Parker Solar Probe to be abundant with Alfvénic velocity spikes and magnetic field kinks. Temperature enhancement is another remarkable feature associated with the Alfvénic spikes. How the prototype of these coincident phenomena is generated intermittently in the source region is an important and wide-ranging subject. Here we propose a new model introducing guide-field discontinuity into the interchange magnetic reconnection between open funnels and closed loops with different magnetic helicities. The modified interchange reconnection model not only can accelerate jet flows from the newly opening closed loop but also can excite and launch Alfvénic wave pulses along the newly reconnected and post-reconnected open flux tubes. We find that the modeling results can reproduce the following observational features: (1) Alfvén disturbance is pulsive in time and asymmetric in space; (2) Alfvénic pulse is compressive with temperature enhancement and density variation inside the pulse. We point out that three physical processes co-happening with Alfvén wave propagation can be responsible for the temperature enhancement: (a) convection of heated jet flow plasmas (decrease in density), (b) propagation of compressive slow-mode waves (increase in density), and (c) conduction of heat flux (weak change in density). We also suggest that the radial nonlinear evolution of the Alfvénic pulses should be taken into account to explain the formation of magnetic switchback geometry.

Keywords: solar wind; alfven waves; solar atmosphere; solar magnetic reconnection
An Updated Shape Model of Dimorphos from DART Data

Dimorphos was the target of the Double Asteroid Redirection Test (DART) mission. This paper summarizes the properties of an updated shape model of Dimorphos, describes the differences between the updated shape model and an earlier version published by Daly, Ernst, Barnouin et al. (doi:10.1038/s41586-023-05810-5), summarizes the data products associated with this model, and explains where the products can be accessed. The updated shape model benefited from improved methods of incorporating limb information, which will accelerate future shape modeling efforts for other objects with limited imaging data. The updated shape model is similar to the earlier model but slightly smaller (‑2.8% change in volume) than the previous Dimorphos global shape model, and the updated shape is slightly more elongated. The additional analysis reported here supports an oblate preimpact shape for Dimorphos. This result indicates that the postimpact elongation of Dimorphos derived from ground-based observations is evidence for a large crater or global reshaping of the asteroid due to the DART impact. The updated global shape model of Dimorphos, as well as the earlier version, will be available in the Planetary Data System Small Bodies Node and through the public Small Body Mapping Tool.

Keywords: asteroid surfaces; near-earth objects; asteroid satellites; space research
Intracluster Magnetic Filaments and an Encounter with a Radio Jet

Thin synchrotron-emitting filaments are increasingly seen in the intracluster medium (ICM). We present the first example of a direct interaction between a magnetic filament, a radio jet, and a dense ICM clump in the poor cluster A194. This enables the first exploration of the dynamics and possible histories of magnetic fields and cosmic rays in such filaments. Our observations are from the MeerKAT Galaxy Cluster Legacy Survey and the LOFAR Two-Meter Sky Survey. Prominent 220 kpc long filaments extend east of radio galaxy 3C40B, with very faint extensions to 300 kpc, and show signs of interaction with its northern jet. They curve around a bend in the jet and intersect the jet in Faraday depth space. The X-ray surface brightness drops across the filaments; this suggests that the relativistic particles and fields contribute significantly to the pressure balance and evacuate the thermal plasma in a ~35 kpc cylinder. We explore whether the relativistic electrons could have streamed along the filaments from 3C40B, and present a plausible alternative whereby magnetized filaments are (a) generated by shear motions in the large-scale, post-merger ICM flow, (b) stretched by interactions with the jet and flows in the ICM, amplifying the embedded magnetic fields, and (c) perfused by re-energized relativistic electrons through betatron-type acceleration or diffusion of turbulently accelerated ICM cosmic-ray electrons. We use the Faraday depth measurements to reconstruct some of the 3D structures of the filameGnts and of 3C40A and B.

Keywords: radio jets; intracluster medium; extragalactic magnetic fields; extragalactic radio sources; plasma physics; poor galaxy clusters; galaxy clusters
MeV-GeV Gamma-Ray Emission from SNR G327.1-1.1 Discovered by the Fermi-LAT

We report the discovery of MeV-GeV γ-ray emission by the Fermi-LAT positionally coincident with the TeV pulsar wind nebula (PWN) HESS J1554-550 within the host supernova remnant (SNR) G327.1-1.1. The γ-ray emission is point-like and faint but significant (>4σ) in the 300 MeV-2 TeV energy range. We report here the Fermi-LAT analysis of the observed γ-ray emission followed by a detailed multiwavelength investigation to understand the nature of the emission. The central pulsar powering the PWN within G327.1-1.1 has not been detected in any wave band; however, it is likely embedded within the X-ray nebula, which is displaced from the center of the radio nebula. The γ-ray emission is faint and therefore a pulsation search to determine if the pulsar may be contributing is not feasible. Prior detailed multiwavelength reports revealed an SNR system that is old, τ ~ 18,000 yr, where the interaction of the reverse shock with the PWN is underway or has recently occurred. We find that the γ-ray emission agrees remarkably well with a detailed broadband model constructed in a prior report based on independent hydrodynamical and semianalytic simulations of an evolved PWN. We further investigate the physical implications of the model for the PWN evolutionary stage incorporating the new Fermi-LAT data and attempt to model the distinct particle components based on a spatial separation analysis of the displaced PWN counterparts.

Keywords: gamma-ray astronomy; pulsar wind nebulae; supernova remnants; x-ray astronomy; spectral energy distribution; radiative processes
Nonlinear Convergence of Solar-like Stars Chromospheres Using Millimeter, Submillimeter, and Infrared Observations

In this work, we present a new methodology to fit the observed and synthetic spectrum of solar-like stars at millimeter, submillimeter, and infrared wavelengths through semiempirical models of the solar chromosphere. We use the Levenberg-Marquardt algorithm as a Nonlinear method, PakalMPI as the semiempirical model of the solar chromosphere, and recent observations from the Atacama Large Millimeter/submillimeter Array of Alpha Centauri A as a test case. Our results show that we can use solar chromospheric semiempirical models as an input model to reproduce the observed spectrum of solar-like stars. The new profiles show similarities to the solar chromosphere as a minimum of temperature (without the restriction from CO emission) and a plateau in the high chromosphere. Our method provides a new fast numerical tool to estimate the physical conditions of solar-like stars.

Keywords: quiet solar chromosphere; stellar chromospheres; millimeter astronomy; submillimeter astronomy; astronomical models; solar electromagnetic emission; algorithms
High-resolution Spectra of Earth-like Planets Orbiting Red Giant Host Stars

In the near future we will have ground- and space-based telescopes that are designed to observe and characterize Earth-like planets. While attention is focused on exoplanets orbiting main-sequence stars, more than 150 exoplanets have already been detected orbiting red giants, opening the intriguing question of what rocky worlds orbiting in the habitable zone (HZ) of red giants would be like and how to characterize them. We present a high-resolution spectral database of reflection and emission spectra for nominal Earth-like planets orbiting in the red giant HZ from the visible to infrared (0.4-20 μm) for planets orbiting at the Earth-equivalent distance. We also show the change of such planetary spectra through the evolution of their red giant hosts. While the luminosity of the host increases the contrast ratio between star and planet, the increased orbital distance of the HZ for red giant hosts relaxes the light suppression requirements close to the star, which could make such planets interesting targets to characterize and search for signs of life, if new coronagraph designs with higher suppression at larger orbital separations could be developed. We assess the feasibility of characterizing atmospheric features including biosignatures for such planets with the proposed mission concept Large UV/Optical/IR Surveyor (LUVOIR).

Keywords: astrobiology; exoplanet atmospheres; exoplanet evolution; habitable zone; habitable planets; stellar evolution; evolved stars; red giant stars; horizontal branch; biosignatures
An APEX Study of Molecular Outflows in FUor-type Stars

The FU Orionis-type objects (FUors) are low-mass pre-main-sequence objects that go through a short-lived phase (~100 yr) of increased mass accretion rate (from 10-8 to 10-4 M ⊙ yr-1). These eruptive young stars are in the early stages of stellar evolution and thus still deeply embedded in a massive envelope that feeds material to the circumstellar disk that is then accreted onto the star. Some FUors drive molecular outflows, i.e., low-velocity wide-angle magnetohydrodynamical winds, that inject energy and momentum back to the surrounding envelopes and help clear the material surrounding the young star. Here we present a 12CO (3-2), 13CO (3-2), and 12CO (4-3) survey of 20 FUor-type eruptive young stars observed with APEX. We use our 13CO (3-2) observations to measure the masses of the envelopes surrounding each FUor and find an agreement with the FUor evolutionary trend found from the 10 μm silicate feature. We find outflows in 11 FUors, calculate their masses and other kinematic properties, and compare these with those of outflows found around quiescent young stellar objects gathered from the literature. This comparison indicates that outflows in FUors are more massive than outflows in quiescent sources, and that FUor outflows have a higher-ratio outflow mass with respect to the envelope than the quiescent sample, indicating that the eruptive young stars have lower star-forming efficiencies. Finally, we find that the outflow forces in FUors are similar to those of quiescent young stellar objects, indicating that their accretion histories are similar or that the FUor outflows have lower velocities.

Keywords: low mass stars; stellar winds; eruptive variable stars; fu orionis stars; circumstellar envelopes
Periodic Activities of Repeating Fast Radio Bursts from Be/X-Ray Binary Systems

The frequency-dependent periodic active window of the fast radio burst FRB 180916.J0158+65 (FRB 180916B) was observed recently. In this letter, we propose that a Be/X-ray binary (BeXRB) system, which is composed of a neutron star (NS) and a Be star with a circumstellar disk, might be the source of a repeating FRB with periodic activities, and we apply this model to explain the activity window of FRB 180916B. The interaction between the NS magnetosphere and the accreted material results in evolution of the spin period and the centrifugal force of the NS, leading to the change of the stress in the NS crust. When the stress of the crust reaches the critical value, a starquake occurs and further produces FRBs. The interval between starquakes is estimated to be a few days, which is smaller than the active window of FRB 180916B. When the NS moves out of the disk of the Be star, the interval between starquakes becomes much longer than the orbital period, which corresponds to the nonactive phase. In this model, due to the absorption of the disk of the Be star, a frequency-dependent active window would appear for the FRBs, which is consistent with the observed properties of FRB 180916B. And the contribution of the dispersion measure from the disk of the Be star is small. In addition, the location of FRB 180916B in the host galaxy is consistent with a BeXRB system.

Keywords: radio transient sources; pulsars; be stars; high mass x-ray binary stars