adsabs/SciX_UAT_keywords huggingface dataset:
Low-mass Galaxy Interactions Trigger Black Hole Activity

The existence of high-z overmassive supermassive black holes represents a major conundrum in our understanding of black hole evolution. In this Letter, we probe from the observational point of view how early Universe environmental conditions could have acted as an evolutionary mechanism for the accelerated growth of the first black holes. Under the assumption that the early Universe is dominated by dwarf galaxies, we investigate the hypothesis that dwarf–dwarf galaxy interactions trigger black hole accretion. We present the discovery of 82 dwarf–dwarf galaxy pairs and 11 dwarf galaxy groups using the Hubble Space Telescope, doubling existing samples. The dwarf systems span a redshift range of 0.13 < z < 1.5, and a stellar mass range of 7.24 < log(M */M ⊙) < 9.73. We performed an X-ray study of a subset of these dwarf systems with Chandra and detected six new active galactic nuclei (AGN), increasing the number of known dwarf–dwarf-merger-related AGN from one to seven. We then compared the frequency of these AGN in grouped/paired dwarfs to that of isolated dwarfs and found a statistically significant enhancement (4σ–6σ) in the interacting sample. This study, the first of its kind at the lowest mass scales, implies that the presence of a nearby dwarf neighbor is efficient in triggering black hole accretion. These results open new avenues for indirect studies of the emergence of the first supermassive black holes.

Keywords: active galactic nuclei; dwarf galaxies; galaxy mergers; supermassive black holes
The Jovian Energetic Ion Environment of Ganymede: Planetary Space Weather Considerations in View of the JUICE Mission

Determining the properties of radiation environments inside planetary magnetospheres is one of the key challenges of planetary space weather science. In this work, we expand our recent simulations of the Jovian energetic ion precipitation to Ganymede's surface to deduce ion circulation patterns at the altitude of ~500 km. We apply a single-particle Monte Carlo model to obtain 3D distribution maps of the H+, O++, and S+++ populations at the altitude of ~500 km. We perform these simulations for three distinct configurations between Ganymede's magnetic field and Jupiter's plasma sheet, characterized by magnetic and electric field conditions similar to those during the NASA Galileo G2, G8, and G28 flybys (i.e., when the moon was above, inside, and below the center of Jupiter's plasma sheet). Our results provide a reference frame for future studies of planetary space weather phenomena in the near-Ganymede region. For ions with energies up to some tens of kiloelectronvolts, we find an increased and spatially extended flow in the anti-Jupiter low-latitude and equatorial regions above Ganymede's leading hemisphere. Our results also show that the ion flux incident at 500 km altitude is not a good approximation of the surface's precipitating flux. To study, therefore, Ganymede's surface erosion processes it may be best to consider also low-altitude orbits as part of future space missions. This study is relevant to the ESA JUpiter ICy moons Explorer mission, which will allow a detailed investigation of the Ganymede environment and its implications on the moon's surface evolution.

Keywords: ganymede
In Situ Observation of Electron Acceleration by a Double Layer in the Bow Shock

The importance of the electric potential along the field direction in the acceleration of electrons in the quasi-perpendicular bow shock has been proposed. Nevertheless, the mechanism by which electrons are accelerated in the bow shock remains unclear from the perspective of in situ observation. In this study, utilizing data obtained by the Magnetospheric Multiscale mission, we identify a double layer (DL) located within the transition layer of the quasi-perpendicular bow shock. It is found that the electric potential generated by this DL corresponds well with an increase in electron parallel temperature, suggesting that the DL can effectively accelerate the electrons in the bow shock. Furthermore, strong whistler emissions have been detected in the vicinity of this DL. It seems that the electrons accelerated by the DL could potentially supply the necessary free energy to excite the observed whistler waves. Thus, the presence of whistler waves provides indirect evidence of an electron beam generated by the DL in bow shock. Our observations demonstrate that the DL can accelerate electrons effectively and impact the electron dynamics within the bow shock.

Keywords: shocks; interplanetary particle acceleration; planetary bow shocks; interplanetary shocks
Implications of Grain Size Distribution and Composition for the Correlation between Dust Extinction and Emissivity

We study the effect of variations in dust size distribution and composition on the correlation between the spectral shape of extinction (parameterized by RV) and far-infrared dust emissivity (parameterized by the power-law index β). Starting from the size distribution models proposed by Weingartner & Draine, using the dust absorption and emission properties derived by Laor & Draine for carbonaceous and silicate grains, and by Li & Draine for polycyclic aromatic hydrocarbon grains, we calculate the extinction and compare it with the reddening vector derived by Schlafly et al. An optimizer and an Markov chain Monte Carlo method are used to explore the space of available parameters for the size distributions. We find that larger grains are correlated with high RV. However, this trend is not enough to explain the emission-extinction correlation observed by Schlafly et al. For the RV - β correlation to arise, we need to impose explicit priors for the carbonaceous and silicate volume priors as functions of RV. The results show that a composition with higher ratio of carbonaceous to silicate grains leads to higher RV and lower β. A relation between E(B - V)/τ353 and RV is apparent, with possible consequences for the recalibration of emission-based dust maps as a function of RV.

Keywords: interstellar dust extinction; interstellar medium; interstellar dust processes; carbonaceous grains; silicate grains; polycyclic aromatic hydrocarbons; interstellar scattering; interstellar absorption
Associated Molecular and Atomic Clouds with X-Ray Shell of Superbubble 30 Doradus C in the LMC

30 Doradus C is a superbubble that emits the brightest non-thermal X- and TeV gamma-rays in the Local Group. To explore the detailed connection between the high-energy radiation and the interstellar medium, we have carried out new CO and HI observations using the Atacama Large Millimeter/Submillimeter Array (ALMA), Atacama Submillimeter Telescope Experiment, and the Australia Telescope Compact Array with resolutions of up to 3 pc. The ALMA data of 12CO(J = 1-0) emission revealed 23 molecular clouds, with typical diameters of ~6-12 pc and masses of ~600-10,000 M⊙. A comparison with the X-rays of XMM-Newton at ~3 pc resolution shows that X-rays are enhanced toward these clouds. The CO data were combined with the HI to estimate the total interstellar protons. A comparison of the interstellar proton column density and the X-rays revealed that the X-rays are enhanced with the total proton column density. These are most likely to be caused by the shock-cloud interaction, which is modeled by magnetohydrodynamical simulations (Inoue et al. 2012). We also note a trend for the X-ray photon index to vary with distance from the center of the high-mass star cluster. This suggests that the cosmic-ray electrons are accelerated by one or multiple supernovae in the cluster. Based on these results, we discuss the role of the interstellar medium in cosmic-ray particle acceleration.

Keywords: cosmic rays; interstellar clouds; superbubbles; supernova remnants; radio astronomy
Scalar Quadratic Maximum-likelihood Estimators for the CMB Cross-power Spectrum

Estimating the cross-correlation power spectra of the cosmic microwave background, in particular, the TB and EB spectra, is important for testing parity symmetry in cosmology and diagnosing insidious instrumental systematics. The quadratic maximum-likelihood (QML) estimator provides optimal estimates of the power spectra, but it is computationally very expensive. The hybrid pseudo-C ℓ estimator is computationally fast but performs poorly on large scales. As a natural extension of previous work, in this article, we present a new unbiased estimator based on the Smith-Zaldarriaga (SZ) approach of E-B separation and the scalar QML approach to reconstruct the cross-correlation power spectrum, called the QML-SZ estimator. Our new estimator relies on the ability to construct scalar maps, which allows us to use a scalar QML estimator to obtain the cross-correlation power spectrum. By reducing the pixel number and algorithm complexity, the computational cost is nearly one order of magnitude smaller and the running time is nearly two orders of magnitude faster in the test situations.

Keywords: cosmic microwave background radiation
Can the Kappa-distributed Electron Energies Account for the Intensity Ratios of O II Lines in Photoionized Gaseous Nebulae?

A vexing puzzle in the study of planetary nebulae and H II regions is that the plasma diagnostic results based on collisionally excited lines systematically differ from those based on recombination lines. A fairly speculative interpretation is the presence of nonthermal electrons with the so-called κ energy distributions, yet there is little observational evidence to verify or disprove this hypothesis. In this paper, we examine the influence of κ-distributed electrons on the emissivities of O II recombination lines using an approximate method, where the rate coefficients for a κ distribution are computed by summing Maxwellian-Boltzmann rate coefficients with appropriate weights. The results show that if invoking κ-distributed electrons, the temperatures derived from the [O III] (λ4959 + λ5007)/λ4363 ratios could coincide with those estimated from the O II λ4649/λ4089 ratios. However, the estimated temperatures and κ values are not in agreement with those obtained through comparing the [O III] (λ4959 + λ5007)/λ4363 ratios and the hydrogen recombination spectra, suggesting that the electron energy is unlikely to follow the κ-distributions over a global scale of the nebular regions. Nevertheless, based on this observation alone, we cannot definitely rule out the presence of κ-distributed electrons in some microstructures within nebulae.

Keywords: h ii regions; planetary nebulae; atomic spectroscopy; plasma astrophysics
The Distribution and Evolution of Quasar Proximity Zone Sizes

In this paper, we study the sizes of quasar proximity zones with synthetic quasar absorption spectra obtained by postprocessing a Cosmic Reionization On Computers (CROC) simulation. CROC simulations have both relatively large box sizes and high spatial resolution, allowing us to resolve Lyman limit systems (LLSs), which are crucial for modeling the quasar absorption spectra. We find that before reionization, most quasar proximity zone sizes grow steadily for ∼10 Myr, while after reionization, they grow rapidly but only for ∼0.1 Myr. We also find a slow growth of Robs with decreasing turn-on redshift. In addition, we find that ∼1%-2% of old quasars (30 Myr old) display extremely small proximity zone sizes (<1 proper Mpc), the vast majority of which are due to the occurrence of a damped Lyα absorber (DLA) or an LLS along the line of sight. These DLAs and LLSs are contaminated with metal, which offers a way to distinguish them from the normal proximity zones of young quasars.

Keywords: quasars; quasar absorption line spectroscopy; reionization; astronomical simulations; radiative transfer simulations; galaxy environments; extragalactic astronomy; lyman limit systems; intergalactic clouds; large-scale structure of the universe
Subsecond Time Evolution of Type III Solar Radio Burst Sources at Fundamental and Harmonic Frequencies

Recent developments in astronomical radio telescopes opened new opportunities in imaging and spectroscopy of solar radio bursts at subsecond timescales. Imaging in narrow frequency bands has revealed temporal variations in the positions and source sizes that do not fit into the standard picture of type III solar radio bursts, and require a better understanding of radio-wave transport. In this paper, we utilize 3D Monte Carlo ray-tracing simulations that account for the anisotropic density turbulence in the inhomogeneous solar corona to quantitatively explain the image dynamics at the fundamental (near plasma frequency) and harmonic (double) plasma emissions observed at ∼32 MHz. Comparing the simulations with observations, we find that anisotropic scattering from an instantaneous emission point source can account for the observed time profiles, centroid locations, and source sizes of the fundamental component of type III radio bursts (generated where fpe ≈ 32 MHz). The best agreement with observations is achieved when the ratio of the perpendicular to the parallel component of the wavevector of anisotropic density turbulence is around 0.25. Harmonic emission sources observed at the same frequency (∼32 MHz, but generated where fpe ≈ 16 MHz) have apparent sizes comparable to those produced by the fundamental emission, but demonstrate a much slower temporal evolution. The simulations of radio-wave propagation make it possible to quantitatively explain the variations of apparent source sizes and positions at subsecond timescales both for the fundamental and harmonic emissions, and can be used as a diagnostic tool for the plasma turbulence in the upper corona.

Keywords: solar radio emission; interplanetary turbulence; radio bursts; solar radio flares
Mildly Relativistic Perpendicular Multiple-ion GRB Shocks

Mildly relativistic perpendicular, collisionless multiple-ion gamma-ray burst shocks are analyzed using 2D3V particle-in-cell simulations. A characteristic feature of multiple-ion shocks is alternating maxima of the α particle and the proton densities, at least in the early downstream. Turbulence, shock-drift acceleration, and evidence of stochastic acceleration are observed. We performed simulations with both in-plane (B y ) and out-of-plane (B z ) magnetic fields, as well as in a perpendicular shock setup with φ = 45°, and saw multiple differences: while with B z , the highest-energetic particles mostly gain energy at the beginning of the shock, with B y , particles continue gaining energy and it does not appear that they have reached their final energy level. A larger magnetization σ leads to more high-energetic particles in our simulations. One important quantity for astronomers is the electron acceleration efficiency ϵ e , which is measurable due to synchrotron radiation. This quantity hardly changes when changing the amount of α particles while keeping σ constant. It is, however, noteworthy that ϵ e strongly differs for in-plane and out-of-plane magnetic fields. When looking at the proton and α acceleration efficiency, ϵ p and ϵ α , the energy of α particles always decreases when passing the shock into the downstream, whereas the energy of protons can increase if α particles account for the majority of the ions.

Keywords: gamma-ray bursts; plasma astrophysics; plasma jets; shocks
How Small-scale Jetlike Solar Events from Miniature Flux Rope Eruptions Might Produce the Solar Wind

We consider small-scale jetlike events that might make the solar wind, as has been suggested in recent studies. We show that the events referred to as "coronal jets" and as "jetlets" both fall on a power-law distribution that also includes large-scale eruptions and spicule-sized features; all of the jetlike events could contribute to the solar wind. Based on imaging and magnetic field data, it is plausible that many or most of these events might form by the same mechanism: Magnetic flux cancelation produces small-scale flux ropes, often containing a cool-material minifilament. This minifilament/flux rope erupts and reconnects with adjacent open coronal field, along which "plasma jets" flow and contribute to the solar wind. The erupting flux ropes can contain twist that is transferred to the open field, and these become Alfvénic pulses that form magnetic switchbacks, providing an intrinsic connection between switchbacks and the production of the solar wind.

Keywords: solar filament eruptions; solar extreme ultraviolet emission; solar magnetic fields; solar wind
Photometry and Kinematics of Self-gravitating Eccentric Nuclear Disks

The Andromeda galaxy hosts an elongated nucleus with (at least) two distinct brightness peaks. The double nucleus can be explained by the projection of a thick, apsidally aligned eccentric nuclear disk of stars in orbit about the central black hole. Several nearby early-type galaxies have similar asymmetric nuclear features, indicating the possible presence of eccentric nuclear disks. We create simulated photometric (surface density) and kinematic (line-of-sight velocity) maps of eccentric nuclear disks using N-body simulations. We image our simulations from various lines of sight in order to classify them as double nuclei, offset nuclei, and centered nuclei. We explore the effects of mass segregation on the photometric maps, finding that heavier stars are concentrated in the brighter peak. The average line-of-sight velocity values are lower in an eccentric nuclear disk than for a circular ring about the supermassive black hole. The velocity dispersion values are higher and peak at the position of the supermassive black hole, which does not typically match the peak in photometry.

Keywords: galaxies; galaxy nuclei
Mass, Spin, and Ultralight Boson Constraints from the Intermediate-mass Black Hole in the Tidal Disruption Event 3XMM J215022.4-055108

We simultaneously and successfully fit the multiepoch X-ray spectra of the tidal disruption event (TDE) 3XMM J215022.4-055108 using a modified version of our relativistic slim disk model that now accounts for angular momentum losses from radiation. We explore the effects of different disk properties and of uncertainties in the spectral hardening factor fc and redshift z on the estimation of the black hole mass M• and spin a•. Across all choices of theoretical priors, we constrain M• to less than 2.2 × 104 M⊙ at 1σ confidence. Assuming that the TDE host is a star cluster associated with the adjacent, brighter, barred lenticular galaxy at z = 0.055, we constrain M• and a• to be ${1.75}_{-0.05}^{+0.45}\times {10}^{4}$ M⊙ and ${0.8}_{-0.02}^{+0.12}$ , respectively, at 1σ confidence. The high, but sub-extremal, spin suggests that, if this intermediate-mass black hole (IMBH) has grown significantly since formation, it has acquired its last e-fold in mass in a way incompatible with both the "standard" and "chaotic" limits of gas accretion. Ours is the first clear IMBH with a spin measurement. As such, this object represents a novel laboratory for astroparticle physics; its M• and a• place tight limits on the existence of ultralight bosons, ruling out those with masses from ~10-15 to 10-16 eV.

Keywords: tidal disruption; x-ray transient sources; accretion; black hole physics; intermediate-mass black holes
Evolutionary Models for 43 Galactic Supernova Remnants with Distances and X-Ray Spectra

The X-ray emission from a supernova remnant (SNR) is a powerful diagnostic of the state of the shocked plasma. The temperature (kT) and the emission measure (EM) of the shocked gas are related to the energy of the explosion, the age of the SNR, and the density of the surrounding medium. Progress in X-ray observations of SNRs has resulted in a significant sample of Galactic SNRs with measured kT and EM values. We apply spherically symmetric SNR evolution models to a new set of 43 SNRs to estimate ages, explosion energies, and circumstellar medium densities. The distribution of ages yields an SNR birth rate. The energies and densities are well fit with lognormal distributions, with wide dispersions. SNRs with two emission components are used to distinguish between SNR models with uniform interstellar medium and with stellar wind environment. We find Type Ia SNRs to be consistent with a stellar wind environment. Inclusion of stellar wind SNR models has a significant effect on estimated lifetimes and explosion energies of SNRs. This reduces the discrepancy between the estimated SNR birth rate and the SN rate of the Galaxy.

Keywords: supernova remnants
Spacetime Hall-MHD Turbulence at Sub-ion Scales: Structures or Waves?

Spatiotemporal properties of two-dimensional (2D) Hall-magnetohydrodynamic (MHD) turbulence at intermediate plasma β = 2 are studied by means of Fast Iterative Filtering (FIF), a new technique for the decomposition of nonstationary nonlinear signals. Results show that the magnetic energy at sub-ion scales is concentrated in perturbations with frequencies smaller than the ion-cyclotron (IC) frequency and with polarization properties that are incompatible with both kinetic Alfvén waves (KAWs) and IC waves. At higher frequencies, we clearly identify signatures of both whistler waves and KAWs; however, their energetic contribution to the magnetic power spectrum is negligible. We conclude that the dynamics of 2D Hall-MHD turbulence at sub-ion scales is mainly driven by localized intermittent structures, with no significant contribution of wavelike fluctuations.

Keywords: space plasmas; solar wind; interplanetary turbulence; plasma astrophysics
The Regulation of Galaxy Growth along the Size-Mass Relation by Star Formation, as Traced by Hα in KMOS3D Galaxies at 0.7 ≲ z ≲ 2.7

We present half-light sizes measured from Hα emission tracing star formation in 281 star-forming galaxies from the KMOS3D survey at 0.7≲ z ≲ 2.7. Sizes are derived by fitting 2D exponential disk models, with bootstrap errors averaging 20%. Hα sizes are a median (mean) of 1.19 (1.26) times larger than those of the stellar continuum—which, due to radial dust gradients, places an upper limit on the growth in stellar size via star formation—with just ∼ 43% intrinsic scatter. At fixed continuum size the Hα size shows no residual trend with stellar mass, star formation rate, redshift, or morphology. The only significant residual trend is with the excess obscuration of Hα by dust, at fixed continuum obscuration. The scatter in continuum size at fixed stellar mass is likely driven by the scatter in halo spin parameters. The stability of the ratio of Hα size to continuum size demonstrates a high degree of stability in halo spin and in the transfer of angular momentum to the disk over a wide range of physical conditions and cosmic time. This may require local regulation by feedback processes. The implication of our results, as we demonstrate using a toy model, is that our upper limit on star-formation-driven growth is sufficient only to evolve star-forming galaxies approximately along the observed size-mass relation, consistent with the size growth of galaxies at constant cumulative comoving number density. To explain the observed evolution of the size-mass relation of star-forming disk galaxies, other processes, such as the preferential quenching of compact galaxies or galaxy mergers, may be required.

Keywords: galaxy evolution; galaxy structure; galaxy disks; star formation; spectroscopy