Table of contents

KASCADE and KASCADE-Grande were multi-detector installations to measure individual air showers of cosmic rays at ultra-high energy. Based on data sets measured by KASCADE and KASCADE-Grande, 90% C.L. upper limits to the flux of gamma-rays in the primary cosmic ray flux are determined in an energy range of ${10}^{14}\mbox{--}{10}^{18}$ eV. The analysis is performed by selecting air showers with a low muon content as expected for gamma-ray-induced showers compared to air showers induced by energetic nuclei. The best upper limit of the fraction of gamma-rays to the total cosmic ray flux is obtained at $3.7\times {10}^{15}$ eV with $1.1\times {10}^{-5}$. Translated to an absolute gamma-ray flux this sets constraints on some fundamental astrophysical models, such as the distance of sources for at least one of the IceCube neutrino excess models.

We examine the linear stability of an isothermal filamentary cloud permeated by a perpendicular magnetic field. Our model cloud is assumed to be supported by gas pressure against self-gravity in the unperturbed state. For simplicity, the density distribution is assumed to be symmetric around the axis. Also for simplicity, the initial magnetic field is assumed to be uniform, and turbulence is not taken into account. The perturbation equation is formulated to be an eigenvalue problem. The growth rate is obtained as a function of the wavenumber for fragmentation along the axis and the magnetic field strength. The growth rate depends critically on the outer boundary. If the displacement vanishes in regions very far from the cloud axis (fixed boundary), cloud fragmentation is suppressed by a moderate magnetic field, which means the plasma beta is below 1.67 on the cloud axis. If the displacement is constant along the magnetic field in regions very far from the cloud, the cloud is unstable even when the magnetic field is infinitely strong. The cloud is deformed by circulation in the plane perpendicular to the magnetic field. The unstable mode is not likely to induce dynamical collapse, since it is excited even when the whole cloud is magnetically subcritical. For both boundary conditions, the magnetic field increases the wavelength of the most unstable mode. We find that the magnetic force suppresses compression perpendicular to the magnetic field especially in regions of low density.

The outburst of V404 Cyg during the summer of 2015 reached unparalleled intensities at X-ray and soft gamma-ray energies with fluxes $\gt 50$ Crab in the 20–50 keV energy band. To date, studies in the hard X-ray/soft gamma-ray energy domain have focused primarily on the energy spectra. In this work, a timing analysis has been performed with INTEGRAL/SPI data in the 20–300 keV energy range for INTEGRAL revolution 1557, which corresponds to the brightest flare of V404 Cyg (on 2015 June 26). The power spectra are fit with broken power-law and multi-Lorentzian models and compared with previously reported results of V404 Cyg flaring activity from 1989 and 2015. Also, we took advantage of the good signal-to-noise ratio obtained above 70 keV to quantify the timing/fast-variability properties of the source as a function of energy. We then point out similarities of V404 Cyg with the black hole transient V4641 Sgr. Like V4641 Sgr, we found that the power spectra of V404 Cyg during high flux periods did not possess the expected flat-top feature typically seen in a hard spectral state. Interpretations are proposed in the framework of the fluctuating-propagation model to explain the observed properties.

We explain the fast-moving, ripple-like features in the edge-on debris disk orbiting the young M dwarf AU Mic. The bright features are clouds of submicron dust repelled by the host star's wind. The clouds are produced by avalanches: radial outflows of dust that gain exponentially more mass as they shatter background disk particles in collisional chain reactions. The avalanches are triggered from a region a few au across—the "avalanche zone"—located on AU Mic's primary "birth" ring at a true distance of ∼35 au from the star but at a projected distance more than a factor of 10 smaller: the avalanche zone sits directly along the line of sight to the star, on the side of the ring nearest Earth, launching clouds that disk rotation sends wholly to the southeast, as observed. The avalanche zone marks where the primary ring intersects a secondary ring of debris left by the catastrophic disruption of a progenitor up to Varuna in size, less than tens of thousands of years ago. Only where the rings intersect are particle collisions sufficiently violent to spawn the submicron dust needed to seed the avalanches. We show that this picture works quantitatively, reproducing the masses, sizes, and velocities of the observed escaping clouds. The Lorentz force exerted by the wind's magnetic field, whose polarity reverses periodically according to the stellar magnetic cycle, promises to explain the observed vertical undulations. The timescale between avalanches, about 10 yr, might be set by time variability of the wind mass loss rate or, more speculatively, by some self-regulating limit cycle.

We present early-time Swift and Chandra X-ray data along with late-time optical and near-infrared observations of SN 2013by, a Type IIL supernova (SN) that occurred in the nearby spiral galaxy ESO 138−G10 (D ∼ 14.8 Mpc). Optical and NIR photometry and spectroscopy follow the late-time evolution of the SN from days +89 to +457 post maximum brightness. The optical spectra and X-ray light curves are consistent with the picture of an SN having prolonged interaction with circumstellar material (CSM) that accelerates the transition from SN to supernova remnant (SNR). Specifically, we find SN 2013by's Hα profile exhibits significant broadening (∼10,000 km s⁻¹) on day +457, the likely consequence of high-velocity, H-rich material being excited by a reverse shock. A relatively flat X-ray light curve is observed that cannot be modeled using Inverse Compton scattering processes alone, but requires an additional energy source most likely originating from the SN-CSM interaction. In addition, we see the first overtone of CO emission near 2.3 μm on day +152, signaling the formation of molecules and dust in the SN ejecta and is the first time CO has been detected in a Type IIL SN. We compare SN 2013by with Type IIP SNe, whose spectra show the rarely observed SN-to-SNR transition in varying degrees and conclude that Type IIL SNe may enter the remnant phase at earlier epochs than their Type IIP counterparts.

We present observations of two new hydrogen-poor superluminous supernovae (SLSN-I), iPTF15esb and iPTF16bad, showing late-time Hα emission with line luminosities of $(1\mbox{--}3)\times {10}^{41}$ erg s⁻¹ and velocity widths of (4000–6000) km s⁻¹. Including the previously published iPTF13ehe, this makes up a total of three such events to date. iPTF13ehe is one of the most luminous and the slowest evolving SLSNe-I, whereas the other two are less luminous and fast decliners. We interpret this as a result of the ejecta running into a neutral H-shell located at a radius of ∼10¹⁶ cm. This implies that violent mass loss must have occurred several decades before the supernova explosion. Such a short time interval suggests that eruptive mass loss could be common shortly before core collapse, and more importantly helium is unlikely to be completely stripped off the progenitor and could be present in the ejecta. It is a mystery why helium features are not detected, even though nonthermal energy sources, capable of ionizing He, may exist as suggested by the O ii absorption series in the early-time spectra. Our late-time spectra (+240 days) appear to have intrinsically lower [O i] 6300 Å luminosities than that of SN2015bn and SN2007bi, which is possibly an indication of less oxygen (<10 M_⊙). The blueshifted Hα emission relative to the hosts for all three events may be in tension with the binary model proposed for iPTF13ehe. Finally, iPTF15esb has a peculiar light curve (LC) with three peaks separated from one another by ∼22 days. The LC undulation is stronger in bluer bands. One possible explanation is ejecta-circumstellar medium interaction.

In the standard picture of structure formation, the first massive galaxies are expected to form at the highest peaks of the density field, which constitute the cores of massive proto-clusters. Luminous quasars (QSOs) at z ∼ 4 are the most strongly clustered population known, and should thus reside in massive dark matter halos surrounded by large overdensities of galaxies, implying a strong QSO–galaxy cross-correlation function. We observed six z ∼ 4 QSO fields with VLT/FORS, exploiting a novel set of narrow-band filters custom designed to select Lyman Break Galaxies (LBGs) in a thin redshift slice of ${\rm{\Delta }}z\sim 0.3$, mitigating the projection effects that have limited the sensitivity of previous searches for galaxies around $z\gtrsim 4$ QSOs. We find that LBGs are strongly clustered around QSOs, and present the first measurement of the QSO–LBG cross-correlation function at z ∼ 4, on scales of $0.1\lesssim R\lesssim 9\,{h}^{-1}\,\mathrm{Mpc}$ (comoving). Assuming a power-law form for the cross-correlation function $\xi ={(r/{r}_{0}^{\mathrm{QG}})}^{\gamma }$, we measure ${r}_{0}^{\mathrm{QG}}={8.83}_{-1.51}^{+1.39}\,{h}^{-1}\,\mathrm{Mpc}$ for a fixed slope of $\gamma =2.0$. This result is in agreement with the expected cross-correlation length deduced from measurements of the QSO and LBG auto-correlation function, and assuming a deterministic bias model. We also measure a strong auto-correlation of LBGs in our QSO fields, finding ${r}_{0}^{\mathrm{GG}}={21.59}_{-1.69}^{+1.72}\,{h}^{-1}\,\mathrm{Mpc}$ for a fixed slope of $\gamma =1.5$, which is ∼4 times larger than the LBG auto-correlation length in blank fields, providing further evidence that QSOs reside in overdensities of LBGs. Our results qualitatively support a picture where luminous QSOs inhabit exceptionally massive (${M}_{\mathrm{halo}}\gt {10}^{12}\,{M}_{\odot }$) dark matter halos at z ∼ 4.

Modern transient surveys have begun discovering and following supernovae (SNe) shortly after first light—providing systematic measurements of the rise of Type II SNe. We explore how analytic models of early shock-cooling emission from core-collapse SNe can constrain the progenitor's radius, explosion velocity, and local host extinction. We simulate synthetic photometry in several realistic observing scenarios; assuming the models describe the typical explosions well, we find that ultraviolet observations can constrain the progenitor's radius to a statistical uncertainty of ±10%–15%, with a systematic uncertainty of ±20%. With these observations the local host extinction (A_V) can be constrained to a factor of two and the shock velocity to ±5% with a systematic uncertainty of ±10%. We also reanalyze the SN light curves presented by Garnavich et al. (2016) and find that KSN 2011a can be fit by a blue supergiant model with a progenitor radius of ${R}_{s}\lt 7.7+8.8(\mathrm{stat})+1.9(\mathrm{sys})\,{R}_{\odot }$, while KSN 2011d can be fit with a red supergiant model with a progenitor radius of ${R}_{s}={111}_{-21(\mathrm{stat})-1(\mathrm{sys})}^{+89(\mathrm{stat})+49(\mathrm{sys})}\,{R}_{\odot }$. Our results do not agree with those of Garnavich et al. Moreover, we re-evaluate their claims and find that there is no statistically significant evidence for a shock-breakout flare in the light curve of KSN 2011d.

We demonstrate a path to hitherto unachievable differential photometric precisions from the ground, both in the optical and near-infrared (NIR), using custom-fabricated beam-shaping diffusers produced using specialized nanofabrication techniques. Such diffusers mold the focal plane image of a star into a broad and stable top-hat shape, minimizing photometric errors due to non-uniform pixel response, atmospheric seeing effects, imperfect guiding, and telescope-induced variable aberrations seen in defocusing. This PSF reshaping significantly increases the achievable dynamic range of our observations, increasing our observing efficiency and thus better averages over scintillation. Diffusers work in both collimated and converging beams. We present diffuser-assisted optical observations demonstrating ${62}_{-16}^{+26}$ ppm precision in 30 minute bins on a nearby bright star 16 Cygni A (V = 5.95) using the ARC 3.5 m telescope—within a factor of ∼2 of Kepler's photometric precision on the same star. We also show a transit of WASP-85-Ab (V = 11.2) and TRES-3b (V = 12.4), where the residuals bin down to ${180}_{-41}^{+66}$ ppm in 30 minute bins for WASP-85-Ab—a factor of ∼4 of the precision achieved by the K2 mission on this target—and to 101 ppm for TRES-3b. In the NIR, where diffusers may provide even more significant improvements over the current state of the art, our preliminary tests demonstrated ${137}_{-36}^{+64}$ ppm precision for a K_S = 10.8 star on the 200 inch Hale Telescope. These photometric precisions match or surpass the expected photometric precisions of TESS for the same magnitude range. This technology is inexpensive, scalable, easily adaptable, and can have an important and immediate impact on the observations of transits and secondary eclipses of exoplanets.

We present an approach for simulating the collisional evolution of spherical isotropic stellar systems based on the one-dimensional Fokker–Planck equation. A novel aspect is that we use the phase volume as the argument of the distribution function instead of the traditionally used energy, which facilitates the solution. The publicly available code PhaseFlow implements a high-accuracy finite-element method for the Fokker–Planck equation, and can handle multiple-component systems, optionally with the central black hole and taking into account loss-cone effects and star formation. We discuss the energy balance in the general setting, and in application to the Bahcall–Wolf cusp around a central black hole, for which we derive a perturbative solution. We stress that the cusp is not a steady-state structure, but rather evolves in amplitude while retaining an approximately $\rho \propto {r}^{-7/4}$ density profile. Finally, we apply the method to the nuclear star cluster of the milky Way, and illustrate a possible evolutionary scenario in which a two-component system of lighter main-sequence stars and stellar-mass black holes develops a Bahcall–Wolf cusp in the heavier component and a weaker $\rho \propto {r}^{-3/2}$ cusp in the lighter, visible component, over the period of several Gyr. The present-day density profile is consistent with the recently detected mild cusp inside the central parsec, and is weakly sensitive to initial conditions.

We present a detailed spectroscopic and photometric analysis of 219 DA and DB white dwarfs for which trigonometric parallax measurements are available. Our aim is to compare the physical parameters derived from the spectroscopic and photometric techniques, and then to test the theoretical mass–radius relation for white dwarfs using these results. The agreement between spectroscopic and photometric parameters is found to be excellent, especially for effective temperatures, showing that our model atmospheres and fitting procedures provide an accurate, internally consistent analysis. The values of surface gravity and solid angle obtained, respectively, from spectroscopy and photometry, are combined with parallax measurements in various ways to study the validity of the mass–radius relation from an empirical point of view. After a thorough examination of our results, we find that 73% and 92% of the white dwarfs are consistent within 1σ and 2σ confidence levels, respectively, with the predictions of the mass–radius relation, thus providing strong support to the theory of stellar degeneracy. Our analysis also allows us to identify 15 stars that are better interpreted in terms of unresolved double degenerate binaries. Atmospheric parameters for both components in these binary systems are obtained using a novel approach. We further identify a few white dwarfs that are possibly composed of an iron core rather than a carbon/oxygen core, since they are consistent with Fe-core evolutionary models.

Identifying the mechanism by which high-energy Lyman continuum (LyC) photons escaped from early galaxies is one of the most pressing questions in cosmic evolution. Haro 11 is the best known local LyC-leaking galaxy, providing an important opportunity to test our understanding of LyC escape. The observed LyC emission in this galaxy presumably originates from one of the three bright, photoionizing knots known as A, B, and C. It is known that Knot C has strong Lyα emission, and Knot B hosts an unusually bright ultraluminous X-ray source, which may be a low-luminosity active galactic nucleus. To clarify the LyC source, we carry out ionization-parameter mapping (IPM) by obtaining narrow-band imaging from the Hubble Space Telescope WFC3 and ACS cameras to construct spatially resolved ratio maps of [O iii]/[O ii] emission from the galaxy. IPM traces the ionization structure of the interstellar medium and allows us to identify optically thin regions. To optimize the continuum subtraction, we introduce a new method for determining the best continuum scale factor derived from the mode of the continuum-subtracted, image flux distribution. We find no conclusive evidence of LyC escape from Knots B or C, but instead we identify a high-ionization region extending over at least 1 kpc from Knot A. This knot shows evidence of an extremely young age (≲1 Myr), perhaps containing very massive stars (>100 M_⊙). It is weak in Lyα, so if it is confirmed as the LyC source, our results imply that LyC emission may be independent of Lyα emission.

Aql X–1 is one of the most prolific low-mass X-ray binary transients (LMXBTs) showing outbursts almost annually. We present the results of our spectral analyses of Rossi X-Ray Timing Explorer/proportional counter-array observations of the 2000 and 2011 outbursts. We investigate the spectral changes related to the changing disk-magnetosphere interaction modes of Aql X–1. The X-ray light curves of the outbursts of LMXBTs typically show phases of fast rise and exponential decay. The decay phase shows a "knee" where the flux goes from the slow-decay to the rapid-decay stage. We assume that the rapid decay corresponds to a weak propeller stage at which a fraction of the inflowing matter in the disk accretes onto the star. We introduce a novel method for inferring, from the light curve, the fraction of the inflowing matter in the disk that accretes onto the neutron star depending on the fastness parameter. We determine the fastness parameter range within which the transition from the accretion to the partial propeller stage is realized. This fastness parameter range is a measure of the scale height of the disk in units of the inner disk radius. We applied the method to a sample of outbursts of Aql X–1 with different maximum flux and duration times. We show that different outbursts with different maximum luminosity and duration follow a similar path in the parameter space of accreted/inflowing mass flux fraction versus fastness parameter.

Abundance anomalies in globular clusters provide strong evidence for multiple stellar populations within each cluster. These populations are usually interpreted as distinct generations, with the currently observed second-generation stars having formed in part from the ejecta of massive, first-generation "polluter" stars, giving rise to the anomalous abundance patterns. The precise nature of the polluters and their enrichment mechanism are still unclear. Even so, the chemical abundances measured in second-generation stars within the globular cluster NGC 2419 provide insight into this puzzling process. Previous work used Monte Carlo nuclear reaction network calculations to constrain the temperature–density conditions that could reproduce the observed abundances, thereby placing robust limits on the origins of the polluter material. The effect of individual reaction rates on these conditions has not been studied, however. Thus, we perform an exhaustive sensitivity study on the nuclear physics input to determine which reactions have the greatest impact on these predictions. We find that the ${}^{30}$Si(p,γ)${}^{31}$P, ${}^{37}$Ar(p,γ)${}^{38}$K, ${}^{38}$Ar(p,γ)${}^{39}$K, and ${}^{39}$K(p,γ)${}^{40}$Ca reactions are all critical in determining the temperature–density conditions, and ultimately, the origins of the polluter material. We conclude with recommendations for future experiments.

GRB 160625B, one of the brightest bursts in recent years, was simultaneously observed by Fermi and Swift satellites, and ground-based optical telescopes in three different events separated by long periods of time. In this paper, the non-thermal multiwavelength observations of GRB 160625B are described and a transition phase from wind-type-like medium to interstellar medium (ISM) between the early (event II) and the late (event III) afterglow is found. The multiwavelength observations of the early afterglow are consistent with the afterglow evolution starting at ∼150 s in a stellar wind medium, whereas the observations of the late afterglow are consistent with the afterglow evolution in ISM. The wind-to-ISM transition is calculated to be at $\sim 8\times {10}^{3}$ s when the jet has decelerated, at a distance of ∼1 pc from the progenitor. Using the standard external shock model, the synchrotron and synchrotron self-Compton emission from reverse shock is required to model the GeV γ-ray and optical observations in the early afterglow, and synchrotron radiation from the adiabatic forward shock to describe the X-ray and optical observations in the late afterglow. The derived values of the magnetization parameter, the slope of the fast decay of the optical flash, and the inferred magnetic fields suggest that Poynting flux-dominated jet models with arbitrary magnetization could account for the spectral properties exhibited by GRB 160625B.

The bright, nearby DA-type white dwarf (WD) 40 Eridani B is orbited by the M dwarf 40 Eri C, allowing determination of the WD's mass. Until recently, however, the mass depended on orbital elements determined four decades ago, and that mass was so low that it created several astrophysical puzzles. Using new astrometric measurements, the binary-star group at the U.S. Naval Observatory has revised the dynamical mass upward, to 0.573 ± 0.018 M_☉. In this paper, we use model-atmosphere analysis to update other parameters of the WD, including effective temperature, surface gravity, radius, and luminosity. We then compare these results with WD interior models. Within the observational uncertainties, theoretical cooling tracks for CO-core WDs of its measured mass are consistent with the position of 40 Eri B in the H-R diagram; equivalently, the theoretical mass–radius relation (MRR) is consistent with the star's location in the mass–radius plane. This consistency is, however, achieved only if we assume a "thin" outer hydrogen layer, with q_H = M_H/M_WD ≃ 10⁻¹⁰. We discuss other evidence that a significant fraction of DA WDs have such thin H layers, in spite of the expectation from canonical stellar-evolution theory of "thick" H layers with q_H ≃ 10⁻⁴. The cooling age of 40 Eri B is ∼122 Myr, and its total age is ∼1.8 Gyr. We present the MRRs for 40 Eri B and three other nearby WDs in visual binaries with precise mass determinations, and show that the agreement of current theory with observations is excellent in all cases.

To study a molecular-cloud-scale chemical composition, we conducted a mapping spectral line survey toward the Galactic molecular cloud W3(OH), which is one of the most active star-forming regions in the Perseus arm. We conducted our survey through the use of the Nobeyama Radio Observatory 45 m telescope, and observed the area of 16' × 16', which corresponds to 9.0 pc × 9.0 pc. The observed frequency ranges are 87–91, 96–103, and 108–112 GHz. We prepared the spectrum averaged over the observed area, in which eight molecular species (CCH, HCN, HCO⁺, HNC, CS, SO, C¹⁸O, and ¹³CO) are identified. On the other hand, the spectrum of the W3(OH) hot core observed at a 0.17 pc resolution shows the lines of various molecules such as OCS, H₂CS CH₃CCH, and CH₃CN in addition to the above species. In the spatially averaged spectrum, emission of the species concentrated just around the star-forming core, such as CH₃OH and HC₃N, is fainter than in the hot core spectrum, whereas emission of the species widely extended over the cloud such as CCH is relatively brighter. We classified the observed area into five subregions according to the integrated intensity of ¹³CO, and evaluated the contribution to the averaged spectrum from each subregion. The CCH, HCN, HCO⁺, and CS lines can be seen even in the spectrum of the subregion with the lowest ¹³CO integrated intensity range (<10 K km s⁻¹). Thus, the contributions of the spatially extended emission is confirmed to be dominant in the spatially averaged spectrum.

Recent observational work has indicated that mechanisms for accretion and outflow in Herbig Ae/Be star–disk systems may differ from magnetospheric accretion (MA) as it is thought to occur in T Tauri star–disk systems. In this work, we assess the temporal evolution of spectral lines probing accretion and mass loss in Herbig Ae/Be systems and test for consistency with the MA paradigm. For two Herbig Ae/Be stars, HD 98922 (B9e) and V1295 Aql (A2e), we have gathered multi-epoch (∼years) and high-cadence (∼minutes) high-resolution optical spectra to probe a wide range of kinematic processes. Employing a line equivalent width evolution correlation metric introduced here, we identify species co-evolving (indicative of common line origin) via novel visualization. We interferometrically constrain often problematically degenerate parameters, inclination and inner-disk radius, allowing us to focus on the structure of the wind, magnetosphere, and inner gaseous disk in radiative transfer models. Over all timescales sampled, the strongest variability occurs within the blueshifted absorption components of the Balmer series lines; the strength of variability increases with the cadence of the observations. Finally, high-resolution spectra allow us to probe substructure within the Balmer series' blueshifted absorption components: we observe static, low-velocity features and time-evolving features at higher velocities. Overall, we find the observed line morphologies and variability are inconsistent with a scaled-up T Tauri MA scenario. We suggest that as magnetic field structure and strength change dramatically with increasing stellar mass from T Tauri to Herbig Ae/Be stars, so too may accretion and outflow processes.

We present BVI surface photometry of 31 dwarf galaxy candidates discovered in a deep image stack from the KMTNet Supernova Program of ∼30 square degrees centered on the nearby NGC 2784 galaxy group. Our final images have a 3σ surface brightness detection limit of ${\mu }_{V}\approx 28.5$ mag arcsec⁻². The faintest central surface brightness that we measure is ${\mu }_{0,V}=26.1$ mag arcsec⁻². If these candidates are at the distance of NGC 2784, then they have absolute magnitudes greater than ${M}_{V}=-9.5$ mag and effective radii larger than 170 pc. Their radial number density decreases exponentially with distance from the center of NGC 2784 until it flattens beyond a radius of 0.5 Mpc. We interpret the baseline density level to represent the background contamination and estimate that 22 of the 31 new candidates are dwarf members of the group. The candidate's average color, $\langle {(B-V)}_{0}\rangle \approx 0.7$, and Sérsic structural parameters are consistent with those parameters for the dwarf populations of other groups. We find that the central population of dwarfs is redder and brighter than the rest of the population. The measured faint-end slope of the luminosity function, $\alpha \approx -1.33$, is steeper than that of the Local Group, but consistent with published results for other groups. Such comparisons are complicated by systematic differences among different studies, but will be simpler when the KMTNet survey, which will provide homogenous data for 15–20 groups, is completed.

Exoplanets discovered over the past decades have provided a new sample of giant exoplanets: hot Jupiters. For lack of enough materials in the current locations of hot Jupiters, they are perceived to form outside the snowline. Then, they migrate to the locations observed through interactions with gas disks or high-eccentricity mechanisms. We examined the efficiencies of different high-eccentricity mechanisms for forming hot Jupiters in near-coplanar multi-planet systems. These mechanisms include planet–planet scattering, the Kozai–Lidov mechanism, coplanar high-eccentricity migration, and secular chaos, as well as other two new mechanisms that we present in this work, which can produce hot Jupiters with high inclinations even in retrograde. We find that the Kozai–Lidov mechanism plays the most important role in producing hot Jupiters among these mechanisms. Secular chaos is not the usual channel for the formation of hot Jupiters due to the lack of an angular momentum deficit within ${10}^{7}{T}_{\mathrm{in}}$ (periods of the inner orbit). According to comparisons between the observations and simulations, we speculate that there are at least two populations of hot Jupiters. One population migrates into the boundary of tidal effects due to interactions with the gas disk, such as ups And b, WASP-47 b, and HIP 14810 b. These systems usually have at least two planets with lower eccentricities, and remain dynamically stable in compact orbital configurations. Another population forms through high-eccentricity mechanisms after the excitation of eccentricity due to dynamical instability. These kinds of hot Jupiters usually have Jupiter-like companions in distant orbits with moderate or high eccentricities.

Coronal mass ejections (CMEs) often exhibit the typical three-part structure in the corona when observed with white-light coronagraphs, i.e., the bright leading front, dark cavity, and bright core, corresponding to a high-low-high density sequence. As CMEs result from eruptions of magnetic flux ropes (MFRs), which can possess either lower (e.g., coronal-cavity MFRs) or higher (e.g., hot-channel MFRs) density compared to their surroundings in the corona, the traditional opinion regards the three-part structure as the manifestations of coronal plasma pileup (high density), coronal-cavity MFR (low density), and filament (high density) contained in the trailing part of MFR, respectively. In this paper, we demonstrate that filament-unrelated CMEs can also exhibit the classical three-part structure. The observations were made from different perspectives through an event that occurred on 2011 October 4. The CME cavity corresponds to the low-density zone between the leading front and the high-density core, and it is obvious in the low corona and gradually becomes fuzzy when propagating outward. The bright core corresponds to a high-density structure that is suggested to be an erupting MFR. The MFR is recorded from both edge-on and face-on perspectives, exhibiting different morphologies that are due to projection effects. We stress that the zone (MFR) with lower (higher) density in comparison to the surroundings can appear as the dark cavity (bright core) when observed through white-light coronagraphs, which is not necessarily the coronal-cavity MFR (erupted filament).

In this paper we use high-resolution cosmological simulations to study halo intrinsic alignment and its dependence on mass, formation time, and large-scale environment. In agreement with previous studies using N-body simulations, it is found that massive halos have stronger alignment. For the first time, we find that for a given halo mass older halos have stronger alignment and halos in cluster regions also have stronger alignment than those in filaments. To model these dependencies, we extend the linear alignment model with inclusion of halo bias and find that the halo alignment with its mass and formation time dependence can be explained by halo bias. However, the model cannot account for the environment dependence, as it is found that halo bias is lower in clusters and higher in filaments. Our results suggest that halo bias and environment are independent factors in determining halo alignment. We also study the halo alignment correlation function and find that halos are strongly clustered along their major axes and less clustered along the minor axes. The correlated halo alignment can extend to scales as large as 100 h⁻¹ Mpc, where its feature is mainly driven by the baryon acoustic oscillation effect.

Current and upcoming radio interferometric experiments are aiming to make a statistical characterization of the high-redshift 21 cm fluctuation signal spanning the hydrogen reionization and X-ray heating epochs of the universe. However, connecting 21 cm statistics to the underlying physical parameters is complicated by the theoretical challenge of modeling the relevant physics at computational speeds quick enough to enable exploration of the high-dimensional and weakly constrained parameter space. In this work, we use machine learning algorithms to build a fast emulator that can accurately mimic an expensive simulation of the 21 cm signal across a wide parameter space. We embed our emulator within a Markov Chain Monte Carlo framework in order to perform Bayesian parameter constraints over a large number of model parameters, including those that govern the Epoch of Reionization, the Epoch of X-ray Heating, and cosmology. As a worked example, we use our emulator to present an updated parameter constraint forecast for the Hydrogen Epoch of Reionization Array experiment, showing that its characterization of a fiducial 21 cm power spectrum will considerably narrow the allowed parameter space of reionization and heating parameters, and could help strengthen Planck's constraints on ${\sigma }_{8}$. We provide both our generalized emulator code and its implementation specifically for 21 cm parameter constraints as publicly available software.

Regarding the strong magnetic field of neutron stars and the high-energy regime scenario that is based on the high-curvature region near the compact objects, one is motivated to study magnetic neutron stars in an energy-dependent spacetime. In this paper, we show that such a strong magnetic field and energy dependency of spacetime have considerable effects on the properties of neutron stars. We examine the variations of maximum mass and related radius, Schwarzschild radius, average density, gravitational redshift, Kretschmann scalar, and Buchdahl theorem due to the magnetic field and energy dependency of the metric. First, it will be shown that the maximum mass and radius of neutron stars are increasing functions of the magnetic field, while average density, redshift, strength of gravity, and Kretschmann scalar are decreasing functions of it. These results are due to a repulsive-like force behavior for the magnetic field. Next, the effects of gravity's rainbow will be studied, and it will be shown that by increasing the rainbow function, the neutron stars could enjoy an expansion in their structures. Then, we obtain a new relation for the upper mass limit of a static spherical neutron star with uniform density in gravity's rainbow (Buchdahl limit) in which such an upper limit is modified as ${M}_{\mathrm{eff}}\lt \tfrac{4{c}^{2}R}{9G}$. In addition, stability and energy conditions for the equation of state of neutron star matter are investigated, and a comparison with empirical results is done. It is notable that the numerical study in this paper is conducted by using the lowest-order constrained variational approach in the presence of a magnetic field employing AV₁₈ potential.

Recent versions of the observed cosmic star formation history (SFH) have resolved an inconsistency with the stellar mass density history. We show that the revised SFH also scales up the delay-time distribution (DTD) of Type Ia supernovae (SNe Ia), as determined from the observed volumetric SN Ia rate history, aligning it with other field-galaxy SN Ia DTD measurements. The revised-SFH-based DTD has a ${t}^{-1.1\pm 0.1}$ form and a Hubble-time-integrated production efficiency of $N/{M}_{\star }=1.3\pm 0.1$ SNe Ia per $1000\,{M}_{\odot }$ of formed stellar mass. Using these revised histories and updated empirical iron yields of the various SN types, we re-derive the cosmic iron accumulation history. Core-collapse SNe and SNe Ia have contributed about equally to the total mass of iron in the universe today. We find the track of the average cosmic gas element in the [α/Fe] versus [Fe/H] abundance-ratio plane. The track is broadly similar to the observed main locus of Galactic stars in this plane, indicating a Milky Way (MW) SFH similar in form to the cosmic one. We easily find a simple MW SFH that makes the track closely match this stellar locus. Galaxy clusters appear to have a higher-normalization DTD. This cluster DTD, combined with a short-burst MW SFH peaked at z = 3, produces a track that matches remarkably well the observed "high-α" locus of MW stars, suggesting the halo/thick-disk population has had a galaxy-cluster-like formation mode. Thus, a simple two-component SFH, combined with empirical DTDs and SN iron yields, suffices to closely reproduce the MW's stellar abundance patterns.

We present results from deep (380 ks) Chandra observations of the active galactic nucleus (AGN) outburst in the massive early-type galaxy NGC 4472. We detect cavities in the gas coincident with the radio lobes and estimate the eastern and western lobe enthalpy to be $(1.1\pm 0.5)\times {10}^{56}$ erg and $(3\pm 1)\times {10}^{56}$ erg and the average power required to inflate the lobes to be $(1.8\pm 0.9)\times {10}^{41}$ erg s⁻¹ and $(6\pm 3)\times {10}^{41}$ erg s⁻¹, respectively. We also detect enhanced X-ray rims around the radio lobes with sharp surface brightness discontinuities between the shells and the ambient gas. The temperature of the gas in the shells is less than that of the ambient medium, suggesting that they are not AGN-driven shocks but rather gas uplifted from the core by the buoyant rise of the radio bubbles. We estimate the energy required to lift the gas to be up to $(1.1\pm 0.3)\times {10}^{56}$ erg and $(3\pm 1)\times {10}^{56}$ erg for the eastern and western rims, respectively, constituting a significant fraction of the total outburst energy. A more conservative estimate suggests that the gas in the rim was uplifted at a smaller distance, requiring only 20%–25% of this energy. In either case, if a significant fraction of this uplift energy is thermalized via hydrodynamic instabilities or thermal conduction, our results suggest that it could be an important source of heating in cool core clusters and groups. We also find evidence for a central abundance drop in NGC 4472. The iron abundance profile shows that the region along the cavity system has a lower metallicity than the surrounding undisturbed gas, similar to the central region. This also shows that bubbles have lifted low-metallicity gas from the center.

We present results from a deep (200 ks) Chandra observation of the early-type galaxy NGC 4552 (M89), which is falling into the Virgo cluster. Previous shallower X-ray observations of this galaxy showed a remnant gas core, a tail to the South of the galaxy, and twin "horns" attached to the northern edge of the gas core. In our deeper data, we detect a diffuse, low surface brightness extension to the previously known tail, and measure the temperature structure within the tail. We combine the deep Chandra data with archival XMM-Newton observations to put a strong upper limit on the diffuse emission of the tail out to a large distance (10× the radius of the remnant core) from the galaxy center. In our two previous papers, we presented the results of hydrodynamical simulations of ram pressure stripping specifically for M89 falling into the Virgo cluster and investigated the effect of intracluster medium (ICM) viscosity. In this paper, we compare our deep data with our specifically tailored simulations and conclude that the observed morphology of the stripped tail in NGC 4552 is most similar to the inviscid models. We conclude that, to the extent the transport processes can be simply modeled as a hydrodynamic viscosity, the ICM viscosity is negligible. More generally, any micro-scale description of the transport processes in the high-β plasma of the cluster ICM must be consistent with the efficient mixing observed in the stripped tail on macroscopic scales.

Galaxy dynamics probe weak gravity at accelerations below the de Sitter scale of acceleration ${a}_{{dS}}={cH}$, where c is the velocity of light and H is the Hubble parameter. Low- and high-redshift galaxies hereby offer a novel probe of weak gravity in an evolving cosmology, satisfying $H(z)={H}_{0}\sqrt{1+{\omega }_{m}(6z+12{z}^{2}+12{z}^{3}+6{z}^{4}+(6/5){z}^{5})}$/$(1+z)$ with matter content ${\omega }_{m}=0.2808\pm 0.028$ sans tension to H₀ in surveys of the local universe. Galaxy rotation curves show anomalous galaxy dynamics in weak gravity ${a}_{N}\lt {a}_{{dS}}$ across a transition radius ${r}_{t}=4.7\,{\rm{kpc}}\,{M}_{11}^{1/2}{({H}_{0}/H)}^{\tfrac{1}{2}}$ in galaxies of mass $M={10}^{11}\,{M}_{\odot }{M}_{11}$, where a_N is the Newtonian acceleration based on baryonic matter content. We identify this behavior with a holographic origin of inertia from entanglement entropy, which introduces a C⁰ onset across ${a}_{N}={a}_{{dS}}$ with asymptotic behavior described by a Milgrom parameter satisfying ${a}_{0}={\omega }_{0}/2\pi$, where ${\omega }_{0}=\sqrt{1-q}H$ is a fundamental eigenfrequency of the cosmological horizon. Extending an earlier confrontation with data covering $0.003\lesssim {a}_{N}/{a}_{{dS}}\lesssim 1$ at redshift $z\sim 0$ in Lellie et al., the modest anomalous behavior in the Genzel et al. sample at redshifts $0.854\leqslant z\leqslant 2.282$ is found to be mostly due to clustering $0.36\lesssim {a}_{N}/{a}_{{dS}}\lesssim 1$ close to the C⁰ onset to weak gravity and an increase of up to 65% in a₀.

One of the most active fields of research of modern-day astrophysics is that of massive black hole formation and coevolution with the host galaxy. In these investigations, ranging from cosmological simulations, to semi-analytical modeling, to observational studies, the Bondi solution for accretion on a central point-mass is widely adopted. In this work we generalize the classical Bondi accretion theory to take into account the effects of the gravitational potential of the host galaxy, and of radiation pressure in the optically thin limit. Then, we present the fully analytical solution, in terms of the Lambert–Euler W-function, for isothermal accretion in Jaffe and Hernquist galaxies with a central black hole. The flow structure is found to be sensitive to the shape of the mass profile of the host galaxy. These results and the formulae that are provided, most importantly, the one for the critical accretion parameter, allow for a direct evaluation of all flow properties, and are then useful for the abovementioned studies. As an application, we examine the departure from the true mass accretion rate of estimates obtained using the gas properties at various distances from the black hole, under the hypothesis of classical Bondi accretion. An overestimate is obtained from regions close to the black hole, and an underestimate outside a few Bondi radii; the exact position of the transition between the two kinds of departure depends on the galaxy model.

We present stacked average far-infrared spectra of a sample of 197 dusty star-forming galaxies (DSFGs) at $0.005\lt z\lt 4$ using about 90% of the Herschel Space Observatory SPIRE Fourier Transform Spectrometer (FTS) extragalactic data archive based on 3.5 years of science operations. These spectra explore an observed-frame 447–1568 GHz frequency range, allowing us to observe the main atomic and molecular lines emitted by gas in the interstellar medium. The sample is subdivided into redshift bins, and a subset of the bins are stacked by infrared luminosity as well. These stacked spectra are used to determine the average gas density and radiation field strength in the photodissociation regions (PDRs) of DSFGs. For the low-redshift sample, we present the average spectral line energy distributions of CO and H₂O rotational transitions and consider PDR conditions based on observed [C i] 370 and 609 μm, and CO (7-6) lines. For the high-z ($0.8\lt z\lt 4$) sample, PDR models suggest a molecular gas distribution in the presence of a radiation field that is at least a factor of 10³ larger than the Milky Way and with a neutral gas density of roughly ${10}^{4.5}$–${10}^{5.5}$ cm⁻³. The corresponding PDR models for the low-z sample suggest a UV radiation field and gas density comparable to those at high-z. Given the challenges in obtaining adequate far-infrared observations, the stacked average spectra we present here will remain the measurements with the highest signal-to-noise ratio for at least a decade and a half until the launch of the next far-infrared facility.

A relativistic spacecraft of the type envisioned by the Breakthrough Starshot initiative will inevitably become charged through collisions with interstellar particles and UV photons. Interstellar magnetic fields would therefore deflect the trajectory of the spacecraft. We calculate the expected deflection for typical interstellar conditions. We also find that the charge distribution of the spacecraft is asymmetric, producing an electric dipole moment. The interaction between the moving electric dipole and the interstellar magnetic field is found to produce a large torque, which can result in fast oscillation of the spacecraft around the axis perpendicular to the direction of motion, with a period of ∼0.5 hr. We then study the spacecraft rotation arising from impulsive torques by dust bombardment. Finally, we discuss the effect of the spacecraft rotation and suggest several methods to mitigate it.

We report flare ribbons approach (FRA) during a multiple-ribbon M-class flare on 2015 November 4 in NOAA AR 12443, obtained by the Interface Region Imaging Spectrograph and the Solar Dynamics Observatory. The flare consisted of a pair of main ribbons and two pairs of secondary ribbons. The two pairs of secondary ribbons were formed later than the appearance of the main ribbons, with respective time delays of 15 and 19 minutes. The negative-polarity main ribbon spread outward faster than the first secondary ribbon with the same polarity in front of it, and thus the FRA was generated. Just before their encounter, the main ribbon was darkening drastically and its intensity decreased by about 70% in 2 minutes, implying the suppression of main-phase reconnection that produced two main ribbons. The FRA caused the deflection of the main ribbon to the direction of secondary ribbon with a deflection angle of about 60°. A post-approach arcade was formed about 2 minutes later and the downflows were detected along the new arcade with velocities of 35–40 km s⁻¹, indicative of the magnetic restructuring during the process of FRA. We suggest that there are three topological domains with footpoints outlined by the three pairs of ribbons. Close proximity of these domains leads to deflection of the ribbons, which is in agreement with the magnetic field topology.

It has recently been proposed that Earth-like planets in the outer regions of the habitable zone experience unstable climates, repeatedly cycling between glaciated and deglaciated climatic states. While this result has been confirmed and also extended to explain early Mars climate records, all existing work relies on highly idealized low-dimensional climate models. Here, we confirm that the phenomenology of climate cycles remains in 3D Earth climate models with considerably more degrees of freedom. To circumvent the computational barrier of integrating climate on Gyr timescales, we implement a hybrid 0D-3D integrator that uses a general circulation model (GCM) as a short relaxation step along a long evolutionary climate sequence. We find that GCM climate cycles are qualitatively consistent with reported low-dimensional results. This establishes on a firmer ground the notion that outer habitable zone planets may be preferentially found in transiently glaciated states.

Almost every star in our Galaxy is likely to harbor a terrestrial planet, but accurate measurements of an exoplanet's mass and radius demand accurate knowledge of the properties of its host star. The imminent TESS and CHEOPS missions are slated to discover thousands of new exoplanets. Along with WFIRST, which will directly image nearby planets, these surveys make urgent the need to better characterize stars in the nearby solar neighborhood (<30 pc). We have compiled the CATalog of Stellar Unified Properties (CATSUP) for 951 stars, including such data as: Gaia astrometry; multiplicity within stellar systems; stellar elemental abundance measurements; standardized spectral types; Ca ii H and K stellar activity indices; GALEX NUV and FUV photometry; and X-ray fluxes and luminosities from ROSAT, XMM, and Chandra. We use this data-rich catalog to find correlations, especially between stellar emission indices, colors, and galactic velocity. Additionally, we demonstrate that thick-disk stars in the sample are generally older, have lower activity, and have higher velocities normal to the galactic plane. We anticipate that CATSUP will be useful for discerning other trends among stars within the nearby solar neighborhood, for comparing thin-disk versus thick-disk stars, for comparing stars with and without planets, and for finding correlations between chemical and kinematic properties.

We present optical integral field spectroscopy for five $z\lt 0.062$ narrow-line Seyfert 1 (NLS1) galaxies, probing their host galaxies at $\gtrsim 2\mbox{--}3\,\mathrm{kpc}$ scales. Emission lines from the active galactic nucleus (AGN) and the large-scale host galaxy are analyzed separately, based on an AGN–host decomposition technique. The host galaxy gas kinematics indicates large-scale gas rotation in all five sources. At the probed scales of $\gtrsim 2\mbox{--}3\,\mathrm{kpc}$, the host galaxy gas is found to be predominantly ionized by star formation without any evidence of a strong AGN contribution. None of the five objects shows specific star formation rates (SFRs) exceeding the main sequence of low-redshift star-forming galaxies. The specific SFRs for MCG-05-01-013 and WPVS 007 are roughly consistent with the main sequence, while ESO 399-IG20, MS 22549-3712, and TON S180 show lower specific SFRs, intermediate to the main sequence and the red quiescent galaxies. The host galaxy metallicities, derived for the two sources with sufficient data quality (ESO 399-IG20 and MCG-05-01-013), indicate central oxygen abundances just below the low-redshift mass–metallicity relation. Based on this initial case study, we outline a comparison of AGN and host galaxy parameters as a starting point for future extended NLS1 studies with similar methods.

Collision-induced absorption (CIA) from molecular hydrogen is a dominant opacity source in the atmosphere of cool white dwarfs. It results in a significant flux depletion in the near-IR and IR parts of their spectra. Because of the extreme conditions of helium-rich atmospheres (where the density can be as high as a few g cm⁻³), this opacity source is expected to undergo strong pressure distortion and the currently used opacities have not been validated at such extreme conditions. To check the distortion of the CIA opacity, we applied state-of-the-art ab initio methods of computational quantum chemistry to simulate the CIA opacity at high densities. The results show that the CIA profiles are significantly distorted above densities of $0.1\,{\rm{g}}\,{\mathrm{cm}}^{-3}$ in a way that is not captured by the existing models. The roto-translational band is enhanced and shifted to higher frequencies as an effect of the decrease of the interatomic separation of the H₂ molecule. The vibrational band is blueward shifted and split into Q_R and Q_P branches, separated by a pronounced interference dip. Its intensity is also substantially reduced. The distortions result in a shift of the maximum of the absorption from 2.3 μm to 3–7 μm, which could potentially explain the spectra of some very cool, helium-rich white dwarfs.

We present a new method for photometering objects in galaxy clusters. We introduce a mode-filtering technique for removing spatially variable backgrounds, improving both detection and photometric accuracy (roughly halving the scatter in the red sequence compared to previous catalogs of the same clusters). This method is based on robustly determining the distribution of background pixel values and should provide comparable improvement in photometric analysis of any crowded fields. We produce new multiwavelength catalogs for the 25 CLASH cluster fields in all 16 bandpasses from the UV through the near-IR, as well as rest-frame magnitudes. A comparison with spectroscopic values from the literature finds a $\sim 30 \%$ decrease in the redshift deviation from previously released CLASH photometry. This improvement in redshift precision, in combination with a detection scheme designed to maximize purity, yields a substantial upgrade in cluster member identification over the previous CLASH galaxy catalog. We construct luminosity functions for each cluster, reliably reaching depths of at least 4.5 mag below M* in every case, and deeper still in several clusters. We measure M* , α, and their redshift evolution, assuming the cluster populations are coeval, and find little to no evolution of $\alpha ,-0.9\lesssim \langle \alpha \rangle \lesssim -0.8$, and M* values consistent with passive evolution. We present a catalog of galaxy photometry, photometric and spectroscopic redshifts, and rest-frame photometry for the full fields of view of all 25 CLASH clusters. Not only will our new photometric catalogs enable new studies of the properties of CLASH clusters, but mode-filtering techniques, such as those presented here, should greatly enhance the data quality of future photometric surveys of crowded fields.

This paper presents a three-dimensional simulation of chromospheric jets with twisted magnetic field lines. Detailed treatments of the photospheric radiative transfer and the equations of state allow us to model realistic thermal convection near the solar surface, which excites various MHD waves and produces chromospheric jets in the simulation. A tall chromospheric jet with a maximum height of 10–11 Mm and lifetime of 8–10 minutes is formed above a strong magnetic field concentration. The magnetic field lines are strongly entangled in the chromosphere, which helps the chromospheric jet to be driven by the Lorentz force. The jet exhibits oscillatory motion as a natural consequence of its generation mechanism. We also find that the produced chromospheric jet forms a cluster with a diameter of several Mm with finer strands. These results imply a close relationship between the simulated jet and solar spicules.

IRIS and EIS observed a GOES C3.1 flare in stare mode on 2014 March 15. The GOES flare started at 00:21:35 and peaked at 00:26:30 UT. The IRIS slit pointed near the center of the flare, while the EIS slit pointed $35^{\prime\prime}$ to its west. About 4 minutes before the GOES flare start, the IRIS C ii and Si iv intensities became (and remained) greater than their pre-flare averages, indicating that the flare had begun and that the chromosphere and transition region were involved. IRIS first detected blueshifted Fe xxi emission at 00:22:42 UT, by which time the C ii and Si iv intensities had increased by factors around 100 and their profiles were redshifted. Simultaneous, cospatial blueshifted Fe xxi emission with redshifted C ii and Si iv emission indicates explosive chromospheric evaporation. EIS spectra reveal Fe xxiii emission that is too weak to measure velocities, and intensity enhancements by factors about 1.7 in the Fe xiv and Fe xvi emission. Lines from both of these coronal ions show redshifts ≈9 km s⁻¹ around 00:24:00 UT, and the Fe xiv 264.7/274.2 intensity ratio reveals an increase of n_e from $(1.03\pm 0.20)\times {10}^{9}$ before to $(3.58\pm 0.68)\times {10}^{9}$ cm⁻³ during the flare. The redshifted coronal line emission and increased n_e are consistent with warm rain falling and accumulating in the remote area observed by EIS. A fit to the RHESSI hard X-ray spectrum yields a nonthermal energy injection rate of $4.9\times {10}^{26}$ erg s⁻¹, from which we estimate a HXR beam energy flux range consistent with explosive evaporation.

Massive circumstellar disks are prone to gravitational instabilities, which trigger the formation of spiral arms that can fragment into bound clumps under the right conditions. Two-dimensional simulations of self-gravitating disks are useful starting points for studying fragmentation because they allow high-resolution simulations of thin disks. However, convergence issues can arise in 2D from various sources. One of these sources is the 2D approximation of self-gravity, which exaggerates the effect of self-gravity on small scales when the potential is not smoothed to account for the assumed vertical extent of the disk. This effect is enhanced by increased resolution, resulting in fragmentation at longer cooling timescales β. If true, it suggests that the 3D simulations of disk fragmentation may not have the same convergence problem and could be used to examine the nature of fragmentation without smoothing self-gravity on scales similar to the disk scale height. To that end, we have carried out local 3D self-gravitating disk simulations with simple β cooling with fixed background irradiation to determine if 3D is necessary to properly describe disk fragmentation. Above a resolution of ∼40 grid cells per scale height, we find that our simulations converge with respect to the cooling timescale. This result converges in agreement with analytic expectations which place a fragmentation boundary at β_crit = 3.

We explore some of the ramifications arising from superflares on the evolutionary history of Earth, other planets in the solar system, and exoplanets. We propose that the most powerful superflares can serve as plausible drivers of extinction events, and that their periodicity corresponds to certain patterns in the terrestrial fossil diversity record. On the other hand, weaker superflares may play a positive role in enabling the origin of life through the formation of key organic compounds. Superflares could also prove to be quite detrimental to the evolution of complex life on present-day Mars and exoplanets in the habitable zone of M- and K-dwarfs. We conclude that the risk posed by superflares has not been sufficiently appreciated, and that humanity might potentially witness a superflare event in the next $\sim {10}^{3}$ years, leading to devastating economic and technological losses. In light of the many uncertainties and assumptions associated with our analysis, we recommend that these results should be viewed with due caution.

We have shown that Lyα blobs (LABs) may still exist even at $z\sim 0.3$, about seven billion years later than most other LABs known (Shirmer et al.). Their luminous Lyα and [O iii] emitters at $z\sim 0.3$ offer new insights into the ionization mechanism. This paper focuses on the two X-ray brightest LABs at $z\sim 0.3$, SDSS J0113+0106 (J0113) and SDSS J1155−0147 (J1155), comparable in size and luminosity to "B1," one of the best-studied LABs at $z\gtrsim 2$. Our NuSTAR hard X-ray (3–30 keV) observations reveal powerful active galactic nuclei (AGN) with ${L}_{2\mbox{--}10\mathrm{keV}}=(0.5\mbox{--}3)\times {10}^{44}$ erg s⁻¹. J0113 also faded by a factor of ∼5 between 2014 and 2016, emphasizing that variable AGN may cause apparent ionization deficits in LABs. Joint spectral analyses including Chandra data constrain column densities of ${N}_{{\rm{H}}}={5.1}_{-3.3}^{+3.1}\times {10}^{23}$ cm⁻² (J0113) and ${N}_{{\rm{H}}}={6.0}_{-1.1}^{+1.4}\times {10}^{22}$ cm⁻² (J1155). J0113 is likely buried in a torus with a narrow ionization cone, but ionizing radiation is also leaking in other directions, as revealed by our Gemini/GMOS 3D spectroscopy. The latter shows a bipolar outflow over 10 kpc, with a peculiar velocity profile that is best explained by AGN flickering. X-ray analysis of J1155 reveals a weakly absorbed AGN that may ionize over a wide solid angle, consistent with our 3D spectra. Extinction-corrected [O iii] log-luminosities are high, ∼43.6. The velocity dispersions are low, ∼100–150 km s⁻¹, even at the AGN positions. We argue that this is a combination of high extinction hiding the turbulent gas and previous outflows that have cleared the escape paths for their successors.

We analyze space- and ground-based data for the old (7.0 ± 0.3 Gyr) solar analogs 16 Cyg A and B. The stars were observed with the Cosmic Origins UV Spectrographs on the Hubble Space Telescope (HST) on 2015 October 23 and 2016 February 3, respectively, and with the Chandra X-ray Observatory on 2016 February 7. Time-series data in Ca ii data are used to place the UV data in context. The UV spectra of 18 Sco (3.7 ± 0.5 Gyr), the Sun (4.6 ± 0.04 Gyr), and α Cen A (${5.4}_{-0.2}^{+1.2}\,\mathrm{Gyr}$) appear remarkably similar, pointing to a convergence of magnetic heating rates for G2 main-sequence stars older than ≈2–4 Gyr. But the B component's X-ray (0.3–2.5 keV) flux lies 20× below a well-known minimum level reported by Schmitt. As reported for α Cen A, the coronal temperature probably lies below that detectable in soft X-rays. No solar UV flux spectra of comparable resolution to those of stellar data exist, but they are badly needed for comparison with stellar data. Center-to-limb variations are reevaluated for lines such as Ca ii through X-rays, with important consequences for observing activity cycles in such features. We also call into question work that has mixed solar intensity–intensity statistics with flux–flux relations of stars.

Photo-z error is one of the major sources of systematics degrading the accuracy of weak-lensing cosmological inferences. Zhang et al. proposed a self-calibration method combining galaxy–galaxy correlations and galaxy–shear correlations between different photo-z bins. Fisher matrix analysis shows that it can determine the rate of photo-z outliers at a level of 0.01%–1% merely using photometric data and do not rely on any prior knowledge. In this paper, we develop a new algorithm to implement this method by solving a constrained nonlinear optimization problem arising in the self-calibration process. Based on the techniques of fixed-point iteration and non-negative matrix factorization, the proposed algorithm can efficiently and robustly reconstruct the scattering probabilities between the true-z and photo-z bins. The algorithm has been tested extensively by applying it to mock data from simulated stage IV weak-lensing projects. We find that the algorithm provides a successful recovery of the scatter rates at the level of 0.01%–1%, and the true mean redshifts of photo-z bins at the level of 0.001, which may satisfy the requirements in future lensing surveys.

We present the first statistical study of the anisotropy of the magnetic field turbulence in the solar wind between 1 and 200 Hz, i.e., from proton to sub-electron scales. We consider 93 ten-minute intervals of the Cluster/STAFF measurements. We find that the fluctuations $\delta {B}_{\perp }^{2}$ are not gyrotropic at a given frequency f, a property already observed at larger scales ($\parallel /\perp$ means parallel/perpendicular to the average magnetic ${{\boldsymbol{B}}}_{0}$). This non-gyrotropy gives indications of the angular distribution of the wave vectors ${\boldsymbol{k}}$: at $f\lt$ 10 Hz, we find that ${k}_{\perp }\gg {k}_{\parallel }$, mainly in the fast wind; at $f\,\gt$ 10 Hz, fluctuations with a non-negligible k_∥ are also present. We then consider the anisotropy ratio $\delta {B}_{\parallel }^{2}/\delta {B}_{\perp }^{2}$, which is a measure of the magnetic compressibility of the fluctuations. This ratio, always smaller than 1, increases with f. It reaches a value showing that the fluctuations are more or less isotropic at electron scales, for $f\geqslant 50\,\mathrm{Hz}$. From 1 to 15–20 Hz, there is a strong correlation between the observed compressibility and the one expected for the kinetic Alfvén waves (KAWs), which only depends on the total plasma β. For $f\gt 15\mbox{--}20\,\mathrm{Hz}$, the observed compressibility is larger than expected for KAWs, and it is stronger in the slow wind: this could be an indication of the presence of a slow-ion acoustic mode of fluctuations, which is more compressive and is favored by the larger values of the electron to proton temperature ratio generally observed in the slow wind.

We report on the second installment of an X-ray monitoring project of seven luminous radio-quiet quasars (RQQs). New Chandra observations of four of these, at $4.10\leqslant z\leqslant 4.35$, yield a total of six X-ray epochs per source, with temporal baselines of $\sim 850\mbox{--}1600$ days in the rest frame. These data provide the best X-ray light curves for RQQs at $z\gt 4$ to date, enabling qualitative investigations of the X-ray variability behavior of such sources for the first time. On average, these sources follow the trend of decreasing variability amplitude with increasing luminosity, and there is no evidence for X-ray variability increasing toward higher redshifts, in contrast with earlier predictions of potential evolutionary scenarios. An ensemble variability structure function reveals that their variability level remains relatively flat across $\approx 20\mbox{--}1000$ days in the rest frame and it is generally lower than that of three similarly luminous RQQs at $1.33\leqslant z\leqslant 2.74$ over the same temporal range. We discuss possible explanations for the increased variability of the lower-redshift subsample and, in particular, whether higher accretion rates play a leading role. Near-simultaneous optical monitoring of the sources at $4.10\leqslant z\leqslant 4.35$ indicates that none is variable on $\approx 1$ day timescales, although flux variations of up to ∼25% are observed on $\approx 100$ day timescales, typical of RQQs at similar redshifts. Significant optical-X-ray spectral slope variations observed in two of these sources are consistent with the levels observed in luminous RQQs and are dominated by X-ray variations.

A critical challenge in the observation of the redshifted 21 cm line is its separation from bright Galactic and extragalactic foregrounds. In particular, the instrumental leakage of polarized foregrounds, which undergo significant Faraday rotation as they propagate through the interstellar medium, may harmfully contaminate the 21 cm power spectrum. We develop a formalism to describe the leakage due to instrumental widefield effects in visibility-based power spectra measured with redundant arrays, extending the delay-spectrum approach presented in Parsons et al. We construct polarized sky models and propagate them through the instrument model to simulate realistic full-sky observations with the Precision Array to Probe the Epoch of Reionization. We find that the leakage due to a population of polarized point sources is expected to be higher than diffuse Galactic polarization at any k mode for a 30 m reference baseline. For the same reference baseline, a foreground-free window at k > 0.3 h Mpc⁻¹ can be defined in terms of leakage from diffuse Galactic polarization even under the most pessimistic assumptions. If measurements of polarized foreground power spectra or a model of polarized foregrounds are given, our method is able to predict the polarization leakage in actual 21 cm observations, potentially enabling its statistical subtraction from the measured 21 cm power spectrum.

This paper is a sequel to our 2015 paper, Kato et al., which calculated the luminosities and spectra of electron-type anti-neutrinos (${\bar{\nu }}_{e}$) from the progenitors of core-collapse supernovae. Expecting that the capability to detect electron-type neutrinos (${\nu }_{e}$) will increase dramatically with the emergence of liquid-argon detectors such as DUNE, we broaden the scope in this study to include all flavors of neutrinos emitted from the pre-bounce phase. We pick up three progenitor models of electron capture supernovae (ECSNe) and iron-core collapse supernovae (FeCCSNe). We find that the number luminosities reach ∼10⁵⁷ s^–1 and ∼10⁵³ s^–1 at maximum for ${\nu }_{e}$ and ${\bar{\nu }}_{e}$, respectively. We also estimate the numbers of detection events at terrestrial neutrino detectors including DUNE, taking flavor oscillations into account and assuming the distance to the progenitors to be 200 pc. It is demonstrated that ${\bar{\nu }}_{e}$ from the ECSN progenitor will be undetected at almost all detectors, whereas we will be able to observe ≳15,900 ${\nu }_{e}$ at DUNE for the inverted mass hierarchy. From the FeCCSN progenitors, the number of ${\bar{\nu }}_{e}$ events will be largest for JUNO, 200–900 ${\bar{\nu }}_{e}$, depending on the mass hierarchy, whereas the number of ${\nu }_{e}$ events at DUNE is $\gtrsim 2100$ for the inverted mass hierarchy. These results imply that the detection of ${\bar{\nu }}_{e}$ is useful to distinguish progenitors of FeCCSNe from those of ECSNe, while ${\nu }_{e}$ will provide us with detailed information on the collapse phase regardless of the type and mass of the progenitor.

We consider the capabilities of current and future large facilities operating at 2–3 mm wavelength to detect and image the [C ii] 158 μm line from galaxies into the cosmic "dark ages" (z ∼ 10–20). The [C ii] line may prove to be a powerful tool in determining spectroscopic redshifts, and galaxy dynamics, for the first galaxies. We emphasize that the nature, and even existence, of such extreme redshift galaxies, remains at the frontier of open questions in galaxy formation. In 40 hr, the Atacama Large Millimeter Array has the sensitivity to detect the integrated [C ii] line emission from a moderate metallicity, active star-forming galaxy $[{Z}_{A}=0.2\,{Z}_{\odot };$ star formation rate $(\mathrm{SFR})=5\,{M}_{\odot }$ yr⁻¹], at z = 10 at a significance of 6σ. The next-generation Very Large Array (ngVLA) will detect the integrated [C ii] line emission from a Milky Way–like SFR galaxy (${Z}_{A}=0.2\,{Z}_{\odot }$, $\mathrm{SFR}=1\,{M}_{\odot }$ yr⁻¹), at z = 15 at a significance of 6σ. Imaging simulations show that the ngVLA can determine rotation dynamics for active star-forming galaxies at $z\sim 15$, if they exist. Based on our very limited knowledge of the extreme redshift universe, we calculate the count rate in blind, volumetric surveys for [C ii] emission at $z\sim 10$–20. The detection rates in blind surveys will be slow (of the order of unity per 40 hr pointing). However, the observations are well suited to commensal searches. We compare [C ii] with the [O iii] 88 μm line, and other ancillary information in high z galaxies that would aid these studies.

We investigate the role of ambipolar diffusion (AD) in collisions between magnetized giant molecular clouds (GMCs), which may be an important mechanism for triggering star cluster formation. Three-dimensional simulations of GMC collisions are performed using a version of the Enzo magnetohydrodynamics code that has been extended to include AD. The resistivities are calculated using the 31-species chemical model of Wu et al. (2015). We find that in the weak-field, $10\ \mu {\rm{G}}$ case, AD has only a modest effect on the dynamical evolution during the collision. However, for the stronger-field, $30\ \mu {\rm{G}}$ case involving near-critical clouds, AD results in the formation of dense cores in regions where collapse is otherwise inhibited. The overall efficiency of formation of cores with ${n}_{{\rm{H}}}\geqslant {10}^{6}\ {\mathrm{cm}}^{-3}$ in these simulations is increases from about 0.2% to 2% once AD is included, comparable to observed values in star-forming GMCs. The gas around these cores typically has relatively slow infall at speeds that are a modest fraction of the free-fall speed.

We present a multiwavelength data analysis of IRAS 05463+2652 (hereafter I05463+2652) to study star formation mechanisms. A shell-like structure around I05463+2652 is evident in the Herschel column density map, which is not associated with any ionized emission. Based on the Herschel submillimeter images, several parsec-scale filaments (including two elongated filaments, "s-fl" and "nw-fl" having lengths of ∼6.4 and ∼8.8 pc, respectively) are investigated in the I05463+2652 site. The Herschel temperature map depicts all these features in a temperature range of ∼11–13 K. 39 clumps are identified and have masses between $\sim 70\mbox{--}945\,{M}_{\odot }$. The majority of clumps (having ${M}_{\mathrm{clump}}\gtrsim 300\,{M}_{\odot }$) are distributed toward the shell-like structure. 175 young stellar objects (YSOs) are selected using the photometric 1–5 μm data and a majority of these YSOs are distributed toward the four areas of high column density ($\gtrsim 5\times {10}^{21}$ cm⁻²; A_V ∼ 5.3 mag) in the shell-like structure, where massive clumps and a spatial association with filament(s) are also observed. The knowledge of observed masses per unit length of elongated filaments and critical mass length reveals that they are supercritical. The filament "nw-fl" is fragmented into five clumps (having ${M}_{\mathrm{clump}}\sim 100\mbox{--}545\,{M}_{\odot }$) and contains noticeable YSOs, while the other filament "s-fl" is fragmented into two clumps (having ${M}_{\mathrm{clump}}\sim 170\mbox{--}215\,{M}_{\odot }$) without YSOs. Together, these observational results favor the role of filaments in the star formation process in I05480+2545. This study also reveals the filament "s-fl," containing two starless clumps, at an early stage of fragmentation.

We study 21 cm and Lyα fluctuations, as well as Hα, while distinguishing between Lyα emission of galactic, diffuse, and scattered intergalactic medium (IGM) origin. Cross-correlation information about the state of the IGM is obtained, testing neutral versus ionized medium cases with different tracers in a seminumerical simulation setup. In order to pave the way toward constraints on reionization history and modeling beyond power spectrum information, we explore parameter dependencies of the cross-power signal between 21 cm and Lyα, which displays a characteristic morphology and a turnover from negative to positive correlation at scales of a couple Mpc⁻¹. In a proof of concept for the extraction of further information on the state of the IGM using different tracers, we demonstrate the use of the 21 cm and Hα cross-correlation signal to determine the relative strength of galactic and IGM emission in Lyα. We conclude by showing the detectability of the 21 cm and Lyα cross-correlation signal over more than one decade in scale at high signal-to-noise ratio for upcoming probes like SKA and the proposed all-sky intensity mapping satellites SPHEREx and CDIM, while also including the Lyα damping tail and 21 cm foreground avoidance in the modeling.

Based on current models of the cosmic X-ray background (CXB), heavily obscured active galactic nuclei (AGNs) are expected to make up ∼10% of the peak emission of the CXB and ∼20% of the total population of AGNs, yet few of these sources have been recorded and characterized in current surveys. Here we present the Chandra follow-up observation of 14 AGNs detected by Swift-BAT. For five sources in the sample, NuSTAR observations in the 3–80 keV band are also available. The X-ray spectral fitting over the 0.3–150 keV energy range allows us to determine the main X-ray spectral parameters, such as the photon index and the intrinsic absorption, of these objects and to make hypotheses on the physical structures responsible for the observed spectra. We find that 13 of the 14 objects are absorbed AGNs, and one is a candidate Compton-thick AGN, having intrinsic absorption ${N}_{{\rm{H}}}\gt {10}^{24}$ cm⁻². Finally, we verified that the use of NuSTAR observations is strategic to strongly constrain the properties of obscured AGNs, since the best-fit values we obtained for parameters such as the power-law photon index Γ and the intrinsic absorption ${N}_{{\rm{H}}}$ changed sometimes significantly fitting the spectra with and without the use of NuSTAR data.

Vortices, turbulence, and unsteady nonlaminar flows are likely both prominent and dynamically important features of astrophysical disks. Such strongly nonlinear phenomena are often difficult, however, to simulate accurately, and are generally amenable to analytic treatment only in idealized form. In this paper, we explore the evolution of compressible two-dimensional flows using an implicit dual-time hydrodynamical scheme that strictly conserves vorticity (if applied to simulate inviscid flows for which Kelvin's Circulation Theorem is applicable). The algorithm is based on the work of Lerat et al., who proposed it in the context of terrestrial applications such as the blade–vortex interactions generated by helicopter rotors. We present several tests of Lerat et al.'s vorticity-preserving approach, which we have implemented to second-order accuracy, providing side-by-side comparisons with other algorithms that are frequently used in protostellar disk simulations. The comparison codes include one based on explicit, second-order van Leer advection, one based on spectral methods, and another that implements a higher-order Godunov solver. Our results suggest that the Lerat et al. algorithm will be useful for simulations of astrophysical environments in which vortices play a dynamical role, and where strong shocks are not expected.

Shell galaxies are understood to form through the collision of a dwarf galaxy with an elliptical galaxy. Shell structures and kinematics have been noted to be independent tools to measure the gravitational potential of the shell galaxies. We compare theoretically the formation of shells in Type I shell galaxies in different gravity theories in this work because this is so far missing in the literature. We include Newtonian plus dark halo gravity, and two non-Newtonian gravity models, MOG and MOND, in identical initial systems. We investigate the effect of dynamical friction, which by slowing down the dwarf galaxy in the dark halo models limits the range of shell radii to low values. Under the same initial conditions, shells appear on a shorter timescale and over a smaller range of distances in the presence of dark matter than in the corresponding non-Newtonian gravity models. If galaxies are embedded in a dark matter halo, then the merging time may be too rapid to allow multi-generation shell formation as required by observed systems because of the large dynamical friction effect. Starting from the same initial state, the observation of small bright shells in the dark halo model should be accompanied by large faint ones, while for the case of MOG, the next shell generation patterns iterate with a specific time delay. The first shell generation pattern shows a degeneracy with the age of the shells and in different theories, but the relative distance of the shells and the shell expansion velocity can break this degeneracy.

We use a sample of 1338 spectroscopically confirmed and photometrically classified Type Ia supernovae (SNe Ia) sourced from Carnegie Supernova Project, Center for Astrophysics Supernova Survey, Sloan Digital Sky Survey-II, and SuperNova Legacy Survey SN samples to examine the relationships between SNe Ia and the galaxies that host them. Our results provide confirmation with improved statistical significance that SNe Ia, after standardization, are on average more luminous in massive hosts (significance >5σ), and decline more rapidly in massive hosts (significance >9σ) and in hosts with low specific star formation rates (significance >8σ). We study the variation of these relationships with redshift and detect no evolution. We split SNe Ia into pairs of subsets that are based on the properties of the hosts and fit cosmological models to each subset. Including both systematic and statistical uncertainties, we do not find any significant shift in the best-fit cosmological parameters between the subsets. Among different SN Ia subsets, we find that SNe Ia in hosts with high specific star formation rates have the least intrinsic scatter (σ_int = 0.08 ± 0.01) in luminosity after standardization.

The white-light STEREO/SECCHI images include light scattered by dust in orbit about the Sun (the F-corona). We analyzed the evolution of the symmetry axis of the F-corona between 2007 and 2012 in the elongation range covered by the STEREO-A/HI-1 instrument (4°–24° elongation) to characterize the plane of symmetry of the zodiacal dust cloud. The symmetry axes both above and below the ecliptic plane were derived separately without assuming any particular functional form. No noticeable time dependence was observed. However, we did find an evolution with elongation of both the inclination i and the ascending node ${{\rm{\Omega }}}_{A}$ of the inferred plane of symmetry. Both parameters appeared fairly constant in the outer half of the elongation range studied ($i=\sim 3\buildrel{\circ}\over{.} 7,{{\rm{\Omega }}}_{A}=\sim 83^\circ ;$ values close to those of Venus's orbit). Then, they start to evolve, becoming $i=\sim 6^\circ$ (i.e., a trend toward the solar equatorial plane) and ${{\rm{\Omega }}}_{A}=\sim 57^\circ$ at about 5° elongation. This variation indicates that the zodiacal dust cloud exhibits a warped plane of symmetry, with an estimated center of symmetry at about $0.5\,{R}_{\odot }$ from the Sun's center on the side of the heliosphere containing Jupiter. We found a marginal difference between the inclination of the axes below and above the ecliptic. This is suggestive of an increased dust density distribution at certain fixed longitudes, which could be explained by the dust deposition of Kreutz Sun-grazing comets. We conjecture that the circumsolar dust is mainly affected by gravitational forces, other forces becoming dominant only where the more rapid changes occur.

Kepler photometry of the hot Neptune host star HAT-P-11 suggests that its spot latitude distribution is comparable to the Sun's near solar maximum. We search for evidence of an activity cycle in the Ca ii H & K chromospheric emission S-index with archival Keck/HIRES spectra and observations from the echelle spectrograph on the Astrophysical Research Consortium 3.5 m Telescope at Apache Point Observatory. The chromospheric emission of HAT-P-11 is consistent with an $\gtrsim 10$ year activity cycle, which plateaued near maximum during the Kepler mission. In the cycle that we observed, the star seemed to spend more time near active maximum than minimum. We compare the $\mathrm{log}{R}_{{HK}}^{{\prime} }$ normalized chromospheric emission index of HAT-P-11 with other stars. HAT-P-11 has unusually strong chromospheric emission compared to planet-hosting stars of similar effective temperature and rotation period, perhaps due to tides raised by its planet.

Modern wide-field, optical time-domain surveys must solve a basic optimization problem: maximize the number of transient discoveries or minimize the follow-up needed for the new discoveries. Here, we describe the Color Me Intrigued experiment, the first from the intermediate Palomar Transient Factory (iPTF) to search for transients simultaneously in the g_PTF and R_PTF bands. During the course of this experiment, we discovered iPTF 16fnm, a new member of the 02cx-like subclass of Type Ia supernovae (SNe). iPTF 16fnm peaked at ${M}_{{g}_{\mathrm{PTF}}}=-15.09\pm 0.17\,\mathrm{mag}$, making it the second-least-luminous known SN Ia. iPTF 16fnm exhibits all the hallmarks of the 02cx-like class: (i) low luminosity at peak, (ii) low ejecta velocities, and (iii) a non-nebular spectrum several months after peak. Spectroscopically, iPTF 16fnm exhibits a striking resemblance to two other low-luminosity 02cx-like SNe: SN 2007qd and SN 2010ae. iPTF 16fnm and SN 2005hk decline at nearly the same rate, despite a 3 mag difference in brightness at peak. When considering the full subclass of 02cx-like SNe, we do not find evidence for a tight correlation between peak luminosity and decline rate in either the g' or r' band. We measure the relative rate of 02cx-like SNe to normal SNe Ia and find ${r}_{{N}_{02{cx}}/{N}_{\mathrm{Ia}}}={33}_{-25}^{+158} \%$. We further examine the g' − r' evolution of 02cx-like SNe and find that their unique color evolution can be used to separate them from 91bg-like and normal SNe Ia. This selection function will be especially important in the spectroscopically incomplete Zwicky Transient Facility/Large Synoptic Survey Telescope (LSST) era. Finally, we close by recommending that LSST periodically evaluate, and possibly update, its observing cadence to maximize transient science.

Halo bias is the one of the key ingredients of the halo models. It was shown at a given redshift to be only dependent, to the first order, on the halo mass. In this study, four types of cosmic web environments—clusters, filaments, sheets, and voids—are defined within a state-of-the-art high-resolution N-body simulation. Within these environments, we use both halo-dark matter cross correlation and halo-halo autocorrelation functions to probe the clustering properties of halos. The nature of the halo bias differs strongly between the four different cosmic web environments described here. With respect to the overall population, halos in clusters have significantly lower biases in the ${10}^{11.0}\sim {10}^{13.5}\,{h}^{-1}\,{M}_{\odot }$ mass range. In other environments, however, halos show extremely enhanced biases up to a factor 10 in voids for halos of mass $\sim {10}^{12.0}\,{h}^{-1}\,{M}_{\odot }$. Such a strong cosmic web environment dependence in the halo bias may play an important role in future cosmological and galaxy formation studies. Within this cosmic web framework, the age dependency of halo bias is found to be only significant in clusters and filaments for relatively small halos $\lesssim {10}^{12.5}\,{h}^{-1}\,{M}_{\odot }$.

We study the prototypical Seyfert 2 galaxy, Markarian 3, based on imaging and high-resolution spectroscopy observations taken by Chandra. We construct a deconvolved X-ray image, which reveals the S-shaped morphology of the hot gas in the narrow-line region (NLR). While this morphology is similar to the radio and [O iii] emission, the distribution of the X-ray gas is broader than that obtained at these other wavelengths. By mapping the density and temperature distribution of the hot gas in the NLR, we demonstrate the presence of shocks toward the west ($M={2.5}_{-0.6}^{+1.0}$) and east ($M={1.5}_{-0.5}^{+1.0}$). Moreover, we compute the flux ratios between the [O iii] and 0.5–2 keV band X-ray luminosity and show that it is nonuniform in the NLR, with the western side of the NLR being more highly ionized. In addition, based on the Chandra grating data, we investigate the line ratios of the Si xiii triplet, which are not consistent with pure photoionization. Based on these results, we suggest that in the NLR of Mrk 3 both photoionization and collisional ionization act as excitation mechanisms. We conclude that the canonical picture, in which photoionization is solely responsible for exciting the interstellar medium in the NLR of Seyfert galaxies, may be overly simplistic. Given that weak and small-scale radio jets are commonly detected in Seyfert galaxies, it is possible that shock heating plays a non-negligible role in the NLR of these galaxies.

The total solar fluxes at 1, 2, 3.75, and 9.4 GHz were observed continuously from 1957 to 1994 at Toyokawa, Japan, and from 1994 until now at Nobeyama, Japan, with the current Nobeyama Radio Polarimeters. We examined the multi-frequency and long-term data sets, and found that not only the microwave solar flux but also its monthly standard deviation indicate the long-term variation of solar activity. Furthermore, we found that the microwave spectra at the solar minima of Cycles 20–24 agree with each other. These results show that the average atmospheric structure above the upper chromosphere in the quiet-Sun has not varied for half a century, and suggest that the energy input for atmospheric heating from the sub-photosphere to the corona have not changed in the quiet-Sun despite significantly differing strengths of magnetic activity in the last five solar cycles.

We simulate anisotropic thermal conduction between the intracluster medium (ICM) and the hot coronal interstellar medium (ISM) gas in cluster galaxies. In Paper I, we simulated the evaporation of the hot ISM due to isotropic (possibly saturated) conduction between the ISM and ICM. We found that hot coronae evaporate on $\sim {10}^{2}\,\mathrm{Myr}$ timescales, significantly shorter than the $\sim {10}^{3}\,\mathrm{Myr}$ gas loss times due to ram pressure stripping. No tails of stripped gas are formed. This is in tension with the observed ubiquity and implied longevity of compact X-ray coronae and stripped ISM tails, and requires the suppression of evaporation, possibly due to magnetic fields and anisotropic conduction. We perform a series of wind tunnel simulations similar to that in Paper I, now including ISM and ICM magnetic fields. We simulate the effect of anisotropic conduction for a range of extreme magnetic field configurations: parallel and perpendicular to the ICM wind, and continuous and completely disjointed between the ISM and ICM. We find that when conduction is anisotropic, gas loss due to evaporation is severely reduced; the overall gas loss rates with and without anisotropic conduction do not differ by more than 10%–20%. Magnetic fields also prevent stripped tails from evaporating in the ICM by shielding, and providing few pathways for heat transport between the ICM and ISM. The morphology of stripped tails and magnetic fields in the tails and wakes of galaxies are sensitive to the initial magnetic field configuration.

NASA's latest MERRA-2 reanalysis of the modern satellite measurements has made atmospheric data easily accessible with unprecedented uniformity, fidelity, and completeness. In this paper, these data are used to evaluate five sites for millimeter-wave (mm-wave) observations. These include two established sites (South Pole and Chajnantor, Atacama), and three new sites (Ali in Tibet, Dome A in Antarctica, and Summit Camp in Greenland). Atmospheric properties including precipitable water vapor (PWV), sky brightness temperature fluctuations, and ice and liquid water paths are derived and compared. Dome A emerges to be the best among those evaluated, with PWV and fluctuations smaller than the second-best site, South Pole, by more than a factor of 2. It is found that the higher site in Ali (6100 m) is on par with Cerro Chajnantor (5612 m) in terms of transmission and stability. The lower site in Ali (5250 m) planned for the first stage of observations at 90/150 GHz provides conditions comparable to those on the Chajnantor Plateau. These analyses confirm Ali to be an excellent mm-wave site in the Northern Hemisphere that will complement well-established Southern sites. According to MERRA-2 data, the observing conditions at Summit Camp are also comparable to Cerro Chajnantor. However, it is more affected by the presence of liquid water clouds.

It is usually thought that a single equation of state (EoS) model "correctly" represents cores of all compact stars. Here we emphasize that two families of compact stars, viz., neutron stars and strange stars, can coexist in nature, and that neutron stars can get converted to strange stars through the nucleation process of quark matter in the stellar center. From our fully general relativistic numerical computations of the structures of fast-spinning compact stars, known as millisecond pulsars, we find that such a stellar conversion causes a simultaneous spin-up and decrease in gravitational mass of these stars. This is a new type of millisecond pulsar evolution through a new mechanism, which gives rise to relatively lower mass compact stars with higher spin rates. This could have an implication for the observed mass and spin distributions of millisecond pulsars. Such a stellar conversion can also rescue some massive, spin-supported millisecond pulsars from collapsing into black holes. Besides, we extend the concept of critical mass ${M}_{\mathrm{cr}}$ for the neutron star sequence to the case of fast-spinning neutron stars, and point out that neutron star EoS models cannot be ruled out by the stellar mass measurement alone. Finally, we emphasize the additional complexity for constraining EoS models, for example, by stellar radius measurements using X-ray observations, if two families of compact stars coexist.

We investigate a new empirical fitting method for the optical light curves of Type Ia supernovae (SNe Ia) that is able to estimate the first-light time of SNe Ia, even when they are not discovered extremely early. With an improved ability to estimate the time of first light for SNe Ia, we compute the rise times for a sample of 56 well-observed SNe Ia. We find rise times ranging from 10.5 to 20.5 days, with a mean of 16.0 days, and confirm that the rise time is generally correlated with the decline rate ${\rm{\Delta }}{m}_{15}(B)$, but with large scatter. The rise time could be an additional parameter to help classify SN Ia subtypes.

The validity of the widely used linear mixing approximation (LMA) for the equations of state (EOSs) of planetary ices is investigated at pressure–temperature conditions typical for the interiors of Uranus and Neptune. The basis of this study is ab initio data ranging up to 1000 GPa and 20,000 K, calculated via density functional theory molecular dynamics simulations. In particular, we determine a new EOS for methane and EOS data for the 1:1 binary mixtures of methane, ammonia, and water, as well as their 2:1:4 ternary mixture. Additionally, the self-diffusion coefficients in the ternary mixture are calculated along three different Uranus interior profiles and compared to the values of the pure compounds. We find that deviations of the LMA from the results of the real mixture are generally small; for the thermal EOSs they amount to 4% or less. The diffusion coefficients in the mixture agree with those of the pure compounds within 20% or better. Finally, a new adiabatic model of Uranus with an inner layer of almost pure ices is developed. The model is consistent with the gravity field data and results in a rather cold interior (${T}_{\mathrm{core}}\sim 4000$ K).

We analyzed series of spectra obtained for 12 stable RRc stars observed with the echelle spectrograph of the du Pont telescope at Las Campanas Observatory and we analyzed the spectra of RRc Blazhko stars discussed by Govea et al. We derived model atmosphere parameters, [Fe/H] metallicities, and [X/Fe] abundance ratios for 12 species of 9 elements. We co-added all spectra obtained during the pulsation cycles to increase signal to noise and demonstrate that these spectra give results superior to those obtained by co-addition in small phase intervals. The RRc abundances are in good agreement with those derived for the RRab stars of Chadid et al. We used radial velocity (RV) measurements of metal lines and Hα to construct variations of velocity with phase, and center-of-mass velocities. We used these to construct RV templates for use in low- to medium-resolution RV surveys of RRc stars. Additionally, we calculated primary accelerations, radius variations, and metal and Hα velocity amplitudes, which we display as regressions against primary acceleration. We employ these results to compare the atmosphere structures of metal-poor RRc stars with their RRab counterparts. Finally, we use the RV data for our Blazhko stars and the Blazhko periods of Szczygieł & Fabrycky to falsify the Blazhko oblique rotator hypothesis.

We present multi-wavelength observations and modeling of the exceptionally bright long γ-ray burst GRB 160625B. The optical and X-ray data are well fit by synchrotron emission from a collimated blastwave with an opening angle of ${\theta }_{j}\approx 3\buildrel{\circ}\over{.} 6$ and kinetic energy of ${E}_{K}\approx 2\times {10}^{51}$ erg, propagating into a low-density ($n\approx 5\times {10}^{-5}$ cm⁻³) medium with a uniform profile. The forward shock is sub-dominant in the radio band; instead, the radio emission is dominated by two additional components. The first component is consistent with emission from a reverse shock, indicating an initial Lorentz factor of ${{\rm{\Gamma }}}_{0}\gtrsim 100$ and an ejecta magnetization of ${R}_{B}\approx 1\mbox{--}100$. The second component exhibits peculiar spectral and temporal evolution and is most likely the result of scattering of the radio emission by the turbulent Milky Way interstellar medium (ISM). Such scattering is expected in any sufficiently compact extragalactic source and has been seen in GRBs before, but the large amplitude and long duration of the variability seen here are qualitatively more similar to extreme scattering events previously observed in quasars, rather than normal interstellar scintillation effects. High-cadence, broadband radio observations of future GRBs are needed to fully characterize such effects, which can sensitively probe the properties of the ISM and must be taken into account before variability intrinsic to the GRB can be interpreted correctly.

The heliospheric magnetic field is of pivotal importance in solar and space physics. The field is rooted in the Sun's photosphere, where it has been observed for many years. Global maps of the solar magnetic field based on full-disk magnetograms are commonly used as boundary conditions for coronal and solar wind models. Two primary observational constraints on the models are (1) the open field regions in the model should approximately correspond to coronal holes (CHs) observed in emission and (2) the magnitude of the open magnetic flux in the model should match that inferred from in situ spacecraft measurements. In this study, we calculate both magnetohydrodynamic and potential field source surface solutions using 14 different magnetic maps produced from five different types of observatory magnetograms, for the time period surrounding 2010 July. We have found that for all of the model/map combinations, models that have CH areas close to observations underestimate the interplanetary magnetic flux, or, conversely, for models to match the interplanetary flux, the modeled open field regions are larger than CHs observed in EUV emission. In an alternative approach, we estimate the open magnetic flux entirely from solar observations by combining automatically detected CHs for Carrington rotation 2098 with observatory synoptic magnetic maps. This approach also underestimates the interplanetary magnetic flux. Our results imply that either typical observatory maps underestimate the Sun's magnetic flux, or a significant portion of the open magnetic flux is not rooted in regions that are obviously dark in EUV and X-ray emission.