Table of contents

During periods of increased solar activity, coronal mass ejections (CMEs) can occur in close succession and proximity to one another. This can lead to the interaction and merger of CME ejecta as they propagate in the heliosphere. The particles accelerated in these shocks can result in complex solar energetic particle (SEP) events, as observing spacecraft form both remote and local shock connections. It can be challenging to understand these complex SEP events from in situ profiles alone. Multipoint observations of CMEs in the near-Sun environment, from the Solar Terrestrial Relations Observatory–Sun Earth Connection Coronal and Heliospheric Investigation and the Solar and Heliospheric Observatory Large Angle and Spectrometric Coronagraph, greatly improve our chances of identifying the origin of these accelerated particles. However, contextual information on conditions in the heliosphere, including the background solar wind conditions and shock structures, is essential for understanding SEP properties well enough to forecast their characteristics. Wang–Sheeley–Arge WSA-ENLIL + Cone modeling provides a tool to interpret major SEP event periods in the context of a realistic heliospheric model and to determine how much of what is observed in large SEP events depends on nonlocal magnetic connections to shock sources. We discuss observations of the SEP-rich periods of 2010 August and 2012 July in conjunction with ENLIL modeling. We find that much SEP activity can only be understood in the light of such models, and in particular from knowing about both remote and local shock source connections. These results must be folded into the investigations of the physics underlying the longitudinal extent of SEP events, and the source connection versus diffusion pictures of interpretations of SEP events.

We present an analysis of physical conditions in the Orion Veil, an atomic photon-dominated region (PDR) that lies just in front (≈2 pc) of the Trapezium stars of Orion. This region offers an unusual opportunity to study the properties of PDRs, including the magnetic field. We have obtained 21 cm H i and 18 cm (1665 and 1667 MHz) OH Zeeman effect data that yield images of the line-of-sight magnetic field strength B_los in atomic and molecular regions of the Veil. We find B_los ≈ −50 to −75 μG in the atomic gas across much of the Veil (25'' resolution) and B_los ≈ −350 μG at one position in the molecular gas (40'' resolution). The Veil has two principal H i velocity components. Magnetic and kinematical data suggest a close connection between these components. They may represent gas on either side of a shock wave preceding a weak-D ionization front. Magnetic fields in the Veil H i components are 3–5 times stronger than they are elsewhere in the interstellar medium where N(H) and n(H) are comparable. The H i components are magnetically subcritical (magnetically dominated), like the cold neutral medium, although they are about 1 dex denser. Comparatively strong fields in the Veil H i components may have resulted from low-turbulence conditions in the diffuse gas that gave rise to OMC-1. Strong fields may also be related to magnetostatic equilibrium that has developed in the Veil since star formation. We also consider the location of the Orion-S molecular core, proposing a location behind the main Orion H⁺ region.

We present Hubble Space Telescope (HST) images for nine megamaser disk galaxies with the primary goal of studying photometric BH-galaxy scaling relations. The megamaser disks provide the highest-precision extragalactic BH mass measurements, while our high-resolution HST imaging affords us the opportunity to decompose the complex nuclei of their late-type hosts in detail. Based on the morphologies and shapes of the galaxy nuclei, we argue that most of these galaxies' central regions contain secularly evolving components (pseudo-bulges), and in many cases we photometrically identify co-existing "classical" bulge components as well. Using these decompositions, we draw the following conclusions. (1) The megamaser BH masses span two orders of magnitude (10⁶–${10}^{8}\;{M}_{\odot }$) while the stellar mass of their spiral host galaxies are all $\sim {10}^{11}\;{M}_{\odot }$ within a factor of three. (2) The BH masses at a given bulge mass or total stellar mass in the megamaser host spiral galaxies tend to be lower than expected when compared to an extrapolation of the BH-bulge relation based on early-type galaxies. (3) The observed large intrinsic scatter of BH masses in the megamaser host galaxies raises the question of whether scaling relations exist in spiral galaxies.

We present new Keck/MOSFIRE K-band spectroscopy for a sample of 14 faint, X-ray-selected active galactic nuclei (AGNs) in the COSMOS field. The data cover the spectral region surrounding the broad Balmer emission lines, which enables the estimation of black hole masses (${M}_{\mathrm{BH}}$) and accretion rates (in terms of $L/{L}_{\mathrm{Edd}}$). We focus on 10 AGNs at z ≃ 3.3, where we observe the Hβ spectral region, while for the other four z ≃ 2.4 sources we use the ${\rm{H}}\alpha$ broad emission line. Compared with previous detailed studies of unobscured AGNs at these high redshifts, our sources are fainter by an order of magnitude, corresponding to number densities of order ∼10⁻⁶–10⁻⁵${\mathrm{Mpc}}^{-3}$. The lower AGN luminosities also allow for a robust identification of the host galaxy emission, necessary to obtain reliable intrinsic AGN luminosities, BH masses and accretion rates. We find the AGNs in our sample to be powered by supermassive black holes (SMBHs) with a typical mass of ${M}_{\mathrm{BH}}\simeq 5\times {10}^{8}\;{M}_{\odot }$—significantly lower than the higher-luminosity, rarer quasars reported in earlier studies. The accretion rates are in the range $L/{L}_{\mathrm{Edd}}$ ∼ 0.1–0.4, with an evident lack of sources with lower $L/{L}_{\mathrm{Edd}}$ (and higher ${M}_{\mathrm{BH}}$), as found in several studies of faint AGNs at intermediate redshifts. Based on the early growth expected for the SMBHs in our sample, we argue that a significant population of faint z ∼ 5−6 AGNs, with ${M}_{\mathrm{BH}}\sim {10}^{6}\;{M}_{\odot }$, should be detectable in the deepest X-ray surveys available, but this is not observed. We discuss several possible explanations for the apparent absence of such a population, concluding that the most probable scenario involves an evolution in source obscuration and/or radiative efficiencies.

We present galaxy stellar mass functions (GSMFs) at z = 4–8 from a rest-frame ultraviolet (UV) selected sample of ∼4500 galaxies, found via photometric redshifts over an area of ∼280 arcmin² in the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS)/Great Observatories Origins Deep Survey (GOODS) fields and the Hubble Ultra Deep Field. The deepest Spitzer/IRAC data to date and the relatively large volume allow us to place a better constraint at both the low- and high-mass ends of the GSMFs compared to previous space-based studies from pre-CANDELS observations. Supplemented by a stacking analysis, we find a linear correlation between the rest-frame UV absolute magnitude at 1500 Å (${M}_{{\rm{UV}}}$) and logarithmic stellar mass ($\mathrm{log}{M}_{* }$) that holds for galaxies with $\mathrm{log}({M}_{* }/{M}_{\odot })\lesssim 10$. We use simulations to validate our method of measuring the slope of the $\mathrm{log}{M}_{* }$–M_UV relation, finding that the bias is minimized with a hybrid technique combining photometry of individual bright galaxies with stacked photometry for faint galaxies. The resultant measured slopes do not significantly evolve over z = 4–8, while the normalization of the trend exhibits a weak evolution toward lower masses at higher redshift. We combine the $\mathrm{log}{M}_{* }$–M_UV distribution with observed rest-frame UV luminosity functions at each redshift to derive the GSMFs, finding that the low-mass-end slope becomes steeper with increasing redshift from $\alpha =-{1.55}_{-0.07}^{+0.08}$ at z = 4 to $\alpha =-{2.25}_{-0.35}^{+0.72}$ at z = 8. The inferred stellar mass density, when integrated over ${M}_{* }={10}^{8}$–10¹³M_⊙, increases by a factor of ${10}_{-2}^{+30}$ between z = 7 and z = 4 and is in good agreement with the time integral of the cosmic star formation rate density.

We present self-consistent, axisymmetric core-collapse supernova simulations performed with the Prometheus-Vertex code for 18 pre-supernova models in the range of 11–28 M_⊙, including progenitors recently investigated by other groups. All models develop explosions, but depending on the progenitor structure, they can be divided into two classes. With a steep density decline at the Si/Si–O interface, the arrival of this interface at the shock front leads to a sudden drop of the mass-accretion rate, triggering a rapid approach to explosion. With a more gradually decreasing accretion rate, it takes longer for the neutrino heating to overcome the accretion ram pressure and explosions set in later. Early explosions are facilitated by high mass-accretion rates after bounce and correspondingly high neutrino luminosities combined with a pronounced drop of the accretion rate and ram pressure at the Si/Si–O interface. Because of rapidly shrinking neutron star radii and receding shock fronts after the passage through their maxima, our models exhibit short advection timescales, which favor the efficient growth of the standing accretion-shock instability. The latter plays a supportive role at least for the initiation of the re-expansion of the stalled shock before runaway. Taking into account the effects of turbulent pressure in the gain layer, we derive a generalized condition for the critical neutrino luminosity that captures the explosion behavior of all models very well. We validate the robustness of our findings by testing the influence of stochasticity, numerical resolution, and approximations in some aspects of the microphysics.

We present measurements of the evolution of normal-galaxy X-ray emission from $z\quad \approx$ 0–7 using local galaxies and galaxy samples in the ≈6 Ms Chandra Deep Field-South (CDF-S) survey. The majority of the CDF-S galaxies are observed at rest-frame energies above 2 keV, where the emission is expected to be dominated by X-ray binary (XRB) populations; however, hot gas is expected to provide small contributions to the observed-frame ≲1 keV emission at z ≲ 1. We show that a single scaling relation between X-ray luminosity (${L}_{{\rm{X}}}$) and star-formation rate (SFR) literature, is insufficient for characterizing the average X-ray emission at all redshifts. We establish that scaling relations involving not only SFR, but also stellar mass (${M}_{\star }$) and redshift, provide significantly improved characterizations of the average X-ray emission from normal galaxy populations at $z\quad \approx$ 0–7. We further provide the first empirical constraints on the redshift evolution of X-ray emission from both low-mass XRB (LMXB) and high-mass XRB (HMXB) populations and their scalings with ${M}_{\star }$ and SFR, respectively. We find ${L}_{2-10\mathrm{keV}}$(LMXB)/${M}_{\star }\propto {(1+z)}^{2-3}$ and ${L}_{2-10\mathrm{keV}}$(HMXB)/SFR $\propto \quad (1+z)$, and show that these relations are consistent with XRB population-synthesis model predictions, which attribute the increase in LMXB and HMXB scaling relations with redshift as being due to declining host galaxy stellar ages and metallicities, respectively. We discuss how emission from XRBs could provide an important source of heating to the intergalactic medium in the early universe, exceeding that of active galactic nuclei.

Recently, the discovery of a Venus-mass planet orbiting a brown-dwarf host in a binary system was reported from the analysis of the microlensing event OGLE-2013-BLG-0723. We reanalyze the event considering the possibility of other interpretations. From this, we find a new solution where the lens is composed of two bodies, in contrast to the three-body solution of the previous analysis. The new solution better explains the observed light curve than the previous solution with Δχ² ∼ 202, suggesting that the new solution is a correct model for the event. From the estimation of the physical parameters based on the new interpretation, we find that the lens system is composed of two low-mass stars with ∼0.2 M_⊙ and ∼0.1 M_⊙ and located at a distance of ∼3 kpc. The fact that the physical parameters correspond to those of the most common lens population located at a distance with a large lensing probability further supports the likelihood of the new interpretation. Considering that two dramatically different solutions can approximately explain the observed light curve, the event suggests the need for carefully testing all possible lens-system geometries.

Unaccounted for systematics from foregrounds and instruments can severely limit the sensitivity of current experiments from detecting redshifted 21 cm signals from the Epoch of Reionization (EoR). Upcoming experiments are faced with a challenge to deliver more collecting area per antenna element without degrading the data with systematics. This paper and its companions show that dishes are viable for achieving this balance using the Hydrogen Epoch of Reionization Array (HERA) as an example. Here, we specifically identify spectral systematics associated with the antenna power pattern as a significant detriment to all EoR experiments which causes the already bright foreground power to leak well beyond ideal limits and contaminate the otherwise clean EoR signal modes. A primary source of this chromaticity is reflections in the antenna-feed assembly and between structures in neighboring antennas. Using precise foreground simulations taking wide-field effects into account, we provide a generic framework to set cosmologically motivated design specifications on these reflections to prevent further EoR signal degradation. We show that HERA will not be impeded by such spectral systematics and demonstrate that even in a conservative scenario that does not perform removal of foregrounds, HERA will detect the EoR signal in line-of-sight k-modes, ${k}_{\parallel }\gtrsim 0.2\;h$ Mpc⁻¹, with high significance. Under these conditions, all baselines in a 19-element HERA layout are capable of detecting EoR over a substantial observing window on the sky.

The observed relation between the X-ray and radio properties of low-luminosity accreting black holes (BHs) has enabled the identification of multiple candidate black hole X-ray binaries (BHXBs) in globular clusters (GCs). Here, we report an identification of the radio source VLA J213002.08+120904 (aka M15 S2), recently reported in Kirsten et al., as a BHXB candidate. They showed that the parallax of this flat-spectrum variable radio source indicates a ${2.2}_{-0.3}^{+0.5}$ kpc distance, which identifies it as lying in the foreground of the GC M15. We determine the radio characteristics of this source and place a deep limit on the X-ray luminosity of ∼4 × 10²⁹ erg s⁻¹. Furthermore, we astrometrically identify a faint red stellar counterpart in archival Hubble images with colors consistent with a foreground star; at 2.2 kpc, its inferred mass is 0.1–0.2 M_⊙. We rule out that this object is a pulsar, neutron star X-ray binary, cataclysmic variable, or planetary nebula, concluding that VLA J213002.08+120904 is the first accreting BHXB candidate discovered in quiescence outside of a GC. Given the relatively small area over which parallax studies of radio sources have been performed, this discovery suggests a much larger population of quiescent BHXBs in our Galaxy, 2.6 × 10⁴–1.7 × 10⁸ BHXBs at 3σ confidence, than has been previously estimated (∼10²–10⁴) through population synthesis.

We present a high-precision measurement of the parallax for the 12-day Cepheid SS Canis Majoris, obtained via spatial scanning with the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST). Spatial scanning enables astrometric measurements with a precision of 20–40 μas, an order of magnitude better than pointed observations. SS CMa is the second Cepheid targeted for parallax measurement with HST and is the first of a sample of 18 long-period (≳10 days) Cepheids selected in order to improve the calibration of their period–luminosity relation and eventually permit a determination of the Hubble constant H₀ to better than 2%. The parallax of SS CMa is found to be 348 ± 38 μas, corresponding to a distance of 2.9 ± 0.3 kpc. We also present a refinement of the static geometric distortion of WFC3 obtained using spatial scanning observations of calibration fields, with a typical magnitude ≲0.01 pixels on scales of 100 pixels.

The Magellanic Clouds provide the only laboratory to study the effects of metallicity and galaxy mass on molecular gas and star formation at high (∼⃒20 pc) resolution. We use the dust emission from HERITAGE Herschel data to map the molecular gas in the Magellanic Clouds, avoiding the known biases of CO emission as a tracer of ${{\rm{H}}}_{2}$. Using our dust-based molecular gas estimates, we find molecular gas depletion times (${\tau }_{{\rm{dep}}}^{{\rm{mol}}}$) of ∼⃒0.4 Gyr in the Large Magellanic Cloud and ∼⃒0.6 in the Small Magellanic Cloud at 1 kpc scales. These depletion times fall within the range found for normal disk galaxies, but are shorter than the average value, which could be due to recent bursts in star formation. We find no evidence for a strong intrinsic dependence of the molecular gas depletion time on metallicity. We study the relationship between the gas and the star formation rate across a range of size scales from 20 pc to ≧̸1 kpc, including how the scatter in ${\tau }_{{\rm{dep}}}^{{\rm{mol}}}$ changes with the size scale, and discuss the physical mechanisms driving the relationships. We compare the metallicity-dependent star formation models of Ostriker et al. and Krumholz to our observations and find that they both predict the trend in the data, suggesting that the inclusion of a diffuse neutral medium is important at lower metallicity.

Estimates of the black hole mass M and the dimensionless spin a in the microquasar GRO J1655-40 implied by strong gravity effects related to the timing and spectral measurements are controversial, if the mass restriction determined by the dynamics related to independent optical measurements, M_opt = (5.4 ± 0.3) M_⊙, is applied. The timing measurements of twin high-frequency (HF) quasiperiodic oscillations (QPOs) with the frequency ratio 3:2 and the simultaneously observed low-frequency (LF) QPO imply spin in the range $a\in (0.27\mbox{--}0.29)$ if models based on the frequencies of geodesic epicyclic motion are used to fit the timing measurements, and the correlated creation of the twin HF QPOs and the LF QPO at a common radius is assumed. On the other hand, the spectral continuum method implies $a\in (0.65\mbox{--}0.75)$, and the Fe-line-profile method implies $a\in (0.94\mbox{--}0.98)$. This controversy can be cured if we abandon the assumption of the occurrence of the twin HF QPOs and the simultaneously observed LF QPO at a common radius. We demonstrate that the epicyclic resonance model of the twin HF QPOs is able to predict the spin in agreement with the Fe-profile method, but no model based on the geodesic epicyclic frequencies can be in agreement with the spectral continuum method. We also show that the non-geodesic string loop oscillation model of twin HF QPOs predicts spin a > 0.3 under the optical measurement limit on the black hole mass, which is in agreement with both the spectral continuum and Fe-profile methods.

We investigate the accretion–ejection process of jets from magnetized accretion disks. We apply a novel approach to the jet-launching problem in order to obtain correlations between the physical properties of the jet and the underlying disk. We extend and confirm the previous works of Tzeferacos et al. and Murphy et al. by scanning a large parameter range for the disk magnetization, ${\mu }_{{\rm{D}}}={10}^{-3.5}...{10}^{-0.7}$. We disentangle the disk magnetization at the foot point of the outflow as the main parameter that governs the properties of the outflow. We show how the four jet integrals known from steady-state MHD are correlated to the disk magnetization at the jet foot point. This agrees with the usual findings of the steady-state theory, however, here we obtain these correlations from time-dependent simulations that include the dynamical evolution of the disk in the treatment. In particular, we obtain robust correlations between the local disk magnetization and (i) the outflow velocity, (ii) the jet mass loading, (iii) the jet angular momentum, and (iv) the local mass accretion rate. Essentially, we find that strongly magnetized disks launch more energetic and faster jets and, due to a larger Alfvén lever arm, these jets extract more angular momentum from the underlying disk. These kinds of disk–jet systems have, however, a smaller mass loading parameter and a lower mass ejection–accretion ratio. The jets are launched at the disk surface where the magnetization is $\mu (r,z)\simeq 0.1$. The magnetization rapidly increases vertically providing the energy reservoir for subsequent jet acceleration. We find indications of a critical disk magnetization ${\mu }_{{\rm{D}}}\simeq 0.01$ that separates the regimes of magneto-centrifugally driven and magnetic pressure-driven jets.

We present a combined analysis of the Chandra and Swift observations of the 2015 X-ray echo of V404 Cygni. Using a stacking analysis, we identify eight separate rings in the echo. We reconstruct the soft X-ray light curve of the 2015 June outburst using the high-resolution Chandra images and cross-correlations of the radial intensity profiles, indicating that about 70% of the outburst fluence occurred during the bright flare at the end of the outburst on MJD 57199.8. By deconvolving the intensity profiles with the reconstructed outburst light curve, we show that the rings correspond to eight separate dust concentrations with precise distance determinations. We further show that the column density of the clouds varies significantly across the field of view, with the centroid of most of the clouds shifted toward the Galactic plane, relative to the position of V404 Cyg, invalidating the assumption of uniform cloud column typically made in attempts to constrain dust properties from light echoes. We present a new XSPEC spectral dust-scattering model that calculates the differential dust-scattering cross section for a range of commonly used dust distributions and compositions and use it to jointly fit the entire set of Swift echo data. We find that a standard Mathis–Rumpl–Nordsieck model provides an adequate fit to the ensemble of echo data. The fit is improved by allowing steeper dust distributions, and models with simple silicate and graphite grains are preferred over models with more complex composition.

We report the results of wide field CO mapping in the region of IRAS 19312+1950. This Infrared Astronomical Satellite (IRAS) object exhibits SiO/H₂O/OH maser emission, and is embedded in a chemically rich molecular component, the origin of which is still unknown. In order to reveal the entire structure and gas mass of the surrounding molecular component for the first time, we have mapped a wide region around IRAS 19312+1950 in the ¹²CO J = 1–0, ¹³CO J = 1–0 and C¹⁸O J = 1–0 lines using the Nobeyama 45 m telescope. In conjunction with archival CO maps, we investigated a region up to 20' × 20' in size around this IRAS object. We calculated the CO gas mass assuming local thermal equilibrium, the stellar velocity through the interstellar medium assuming an analytic model of bow shock, and the absolute luminosity, using the latest archival data and trigonometric parallax distance. The derived gas mass (225 M_⊙–478 M_⊙) of the molecular component and the relatively large luminosity (2.63 × 10⁴L_☉) suggest that the central SiO/H₂O/OH maser source is a red supergiant rather than an asymptotic giant branch (AGB) star or post-AGB star.

The two-point diagnostics Om(z_i, z_j) and Omh²(z_i, z_j) have been introduced as an interesting tool for testing the validity of the Λ cold dark matter (ΛCDM) model. Recently, Sahni et al. combined two independent measurements of H(z) from baryon acoustic oscillation (BAO) data with the value of the Hubble constant H₀, and used the second of these diagnostics to test the ΛCDM (a constant equation-of-state parameter for dark energy) model. Their result indicated a considerable tension between observations and predictions of the ΛCDM model. Since reliable data concerning the expansion rates of the universe at different redshifts H(z) are crucial for the successful application of this method, we investigate both two-point diagnostics on the most comprehensive set of N = 36 measurements of H(z) from BAOs and the differential ages (DAs) of passively evolving galaxies. We discuss the uncertainties of the two-point diagnostics and find that they are strongly non-Gaussian and follow the patterns deeply rooted in their very construction. Therefore we propose that non-parametric median statistics is the most appropriate way of treating this problem. Our results support the claims that ΛCDM is in tension with H(z) data according to the two-point diagnostics developed by Shafieloo, Sahni, and Starobinsky. However, other alternatives to the ΛCDM model, such as the wCDM or Chevalier–Polarski–Linder models, perform even worse. We also note that there are serious systematic differences between the BAO and DA methods that ought to be better understood before H(z) measurements can compete with other probes methods.

Pulsars are rapidly spinning and highly magnetized neutron stars, with highly stable rotational periods and a gradual spin-down over a long timescale due to the loss of radiation. Glitches refer to events that suddenly increase the rotational speed of a pulsar. The exact causes of glitches and the resulting processes are not fully understood. It is generally believed that couplings between the normal matter and superfluid components, and starquakes, are the common causes of glitches. In this study, one famous glitching pulsar, PSR J2021+4026, is investigated. PSR J2021+4026 is the first variable gamma-ray pulsar observed by Fermi. From gamma-ray observations, it is found that the pulsar experienced a significant flux drop, an increase in the spin-down rate, a change in the pulse profile and a shift in the spectral cut-off to a lower energy, simultaneously around 2011 October 16. To explain these effects on high-energy emissions by the glitch of PSR J2021+4026, we hypothesized the glitch to be caused by the rearrangement of the surface magnetic field due to crustal plate tectonic activities on the pulsar, which was triggered by a starquake. In this glitch event, the inclination angle of the magnetic dipole axis was slightly shifted. This proposition is then tested by numerical modeling using a three-dimensional two-layer outer gap model. The simulation results indicate that a modification of the inclination angle can affect the pulse profile and the spectral properties, which can explain the observation changes after the glitch.

The Kepler Mission has discovered thousands of planets with radii <4 ${R}_{\oplus }$, paving the way for the first statistical studies of the dynamics, formation, and evolution of these sub-Neptunes and super-Earths. Planetary masses are an important physical property for these studies, and yet the vast majority of Kepler planet candidates do not have theirs measured. A key concern is therefore how to map the measured radii to mass estimates in this Earth-to-Neptune size range where there are no Solar System analogs. Previous works have derived deterministic, one-to-one relationships between radius and mass. However, if these planets span a range of compositions as expected, then an intrinsic scatter about this relationship must exist in the population. Here we present the first probabilistic mass–radius relationship (M–R relation) evaluated within a Bayesian framework, which both quantifies this intrinsic dispersion and the uncertainties on the M–R relation parameters. We analyze how the results depend on the radius range of the sample, and on how the masses were measured. Assuming that the M–R relation can be described as a power law with a dispersion that is constant and normally distributed, we find that $M/{M}_{\oplus }=2.7{(R/{R}_{\oplus })}^{1.3}$, a scatter in mass of $1.9{M}_{\oplus }$, and a mass constraint to physically plausible densities, is the "best-fit" probabilistic M–R relation for the sample of RV-measured transiting sub-Neptunes (R_pl < 4 ${R}_{\oplus }$). More broadly, this work provides a framework for further analyses of the M–R relation and its probable dependencies on period and stellar properties.

We present deep optical images of the Large and Small Magellanic Clouds (LMC and SMC) using a low cost telephoto lens with a wide field of view to explore stellar substructure in the outskirts of the stellar disk of the LMC (<10° from the LMC center). These data have higher resolution than existing star count maps, and highlight the existence of stellar arcs and multiple spiral arms in the northern periphery, with no comparable counterparts in the south. We compare these data to detailed simulations of the LMC disk outskirts, following interactions with its low mass companion, the SMC. We consider interaction in isolation and with the inclusion of the Milky Way tidal field. The simulations are used to assess the origin of the northern structures, including also the low density stellar arc recently identified in the Dark Energy Survey data by Mackey et al. at ∼15°. We conclude that repeated close interactions with the SMC are primarily responsible for the asymmetric stellar structures seen in the periphery of the LMC. The orientation and density of these arcs can be used to constrain the LMC's interaction history with and impact parameter of the SMC. More generally, we find that such asymmetric structures should be ubiquitous about pairs of dwarfs and can persist for 1–2 Gyr even after the secondary merges entirely with the primary. As such, the lack of a companion around a Magellanic Irregular does not disprove the hypothesis that their asymmetric structures are driven by dwarf–dwarf interactions.

We present a method for analyzing the interaction between radiation and matter in regions of intense, relativistic shear that can arise in many astrophysical situations. We show that there is a simple velocity profile that should be manifested in regions of large shear that have "lost memory" of their boundary conditions, and we use this self-similar velocity profile to construct the surface of last scattering, or the $\tau \simeq 1$ surface, as viewed from any comoving point within the flow. We demonstrate that a simple treatment of scattering from this $\tau \simeq 1$ surface exactly conserves photon number, and we derive the rate at which the radiation field is heated due to the shear present in the flow. The components of the comoving radiation energy–momentum tensor are calculated, and we show that they have relatively simple, approximate forms that interpolate between the viscous (small shear) and streaming (large shear) limits. We put our expression for the energy–momentum tensor in a covariant form that does not depend on the explicit velocity profile within the fluid and, therefore, represents a natural means for analyzing general, radiation-dominated, relativistic shear flows.

The so-called "unidentified" infrared emission (UIE) features at 3.3, 6.2, 7.7, 8.6, and 11.3 μm are ubiquitously seen in a wide variety of astrophysical regions. The UIE features are characteristic of the stretching and bending vibrations of aromatic hydrocarbon materials, e.g., polycyclic aromatic hydrocarbon (PAH) molecules. The 3.3 μm aromatic C–H stretching feature is often accompanied by a weaker feature at 3.4 μm. The latter is generally thought to result from the C–H stretch of aliphatic groups attached to the aromatic systems. The ratio of the observed intensity of the 3.3 μm aromatic C–H feature to that of the 3.4 μm aliphatic C–H feature allows one to estimate the aliphatic fraction of the UIE carriers, provided that the intrinsic oscillator strengths of the 3.3 μm aromatic C–H stretch (${A}_{3.3}$) and the 3.4 μm aliphatic C–H stretch (${A}_{3.4}$) are known. While previous studies on the aliphatic fraction of the UIE carriers were mostly based on the ${A}_{3.4}/{A}_{3.3}$ ratios derived from the mono-methyl derivatives of small PAH molecules, in this work we employ density functional theory to compute the infrared vibrational spectra of PAH molecules with a wide range of sidegroups including ethyl, propyl, butyl, and several unsaturated alkyl chains, as well as all the isomers of dimethyl-substituted pyrene. We find that, except for PAHs with unsaturated alkyl chains, the corresponding ${A}_{3.4}/{A}_{3.3}$ ratios are close to that of mono-methyl PAHs. This confirms the predominantly aromatic nature of the UIE carriers previously inferred from the ${A}_{3.4}/{A}_{3.3}$ ratio derived from mono-methyl PAHs.

Large-scale dynamo action is well understood when the magnetic Reynolds number (Rm) is small, but becomes problematic in the astrophysically relevant large Rm limit since the fluctuations may control the operation of the dynamo, obscuring the large-scale behavior. Recent works by Tobias & Cattaneo demonstrated numerically the existence of large-scale dynamo action in the form of dynamo waves driven by strongly helical turbulence and shear. Their calculations were carried out in the kinematic regime in which the back-reaction of the Lorentz force on the flow is neglected. Here, we have undertaken a systematic extension of their work to the fully nonlinear regime. Helical turbulence and large-scale shear are produced self-consistently by prescribing body forces that, in the kinematic regime, drive flows that resemble the original velocity used by Tobias & Cattaneo. We have found four different solution types in the nonlinear regime for various ratios of the fluctuating velocity to the shear and Reynolds numbers. Some of the solutions are in the form of propagating waves. Some solutions show large-scale helical magnetic structure. Both waves and structures are permanent only when the kinetic helicity is non-zero on average.

We present an improved and extended analysis of the cross-correlation between the map of the cosmic microwave background (CMB) lensing potential derived from the Planck mission data and the high-redshift galaxies detected by the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) in the photometric redshift range ${z}_{{\rm{ph}}}\geqslant 1.5$. We compare the results based on the 2013 and 2015 Planck datasets, and investigate the impact of different selections of the H-ATLAS galaxy samples. Significant improvements over our previous analysis have been achieved thanks to the higher signal-to-noise ratio of the new CMB lensing map recently released by the Planck collaboration. The effective galaxy bias parameter, b, for the full galaxy sample, derived from a joint analysis of the cross-power spectrum and of the galaxy auto-power spectrum is found to be $b={3.54}_{-0.14}^{+0.15}$. Furthermore, a first tomographic analysis of the cross-correlation signal is implemented by splitting the galaxy sample into two redshift intervals: $1.5\leqslant {z}_{{\rm{ph}}}\lt 2.1$ and ${z}_{{\rm{ph}}}\geqslant 2.1$. A statistically significant signal was found for both bins, indicating a substantial increase with redshift of the bias parameter: $b=2.89\pm 0.23$ for the lower and $b={4.75}_{-0.25}^{+0.24}$ for the higher redshift bin. Consistent with our previous analysis, we find that the amplitude of the cross-correlation signal is a factor of ${1.45}_{-0.13}^{+0.14}$ higher than expected from the standard ΛCDM model for the assumed redshift distribution. The robustness of our results against possible systematic effects has been extensively discussed, although the tension is mitigated by passing from 4 to 3σ.

We exploit the widely separated images of the lensed quasar SDSS J1029+2623 (${z}_{\mathrm{em}}$ = 2.197, θ = 225) to observe its outflowing wind through two different sightlines. We present an analysis of three observations, including two with the Subaru telescope in 2010 February and 2014 April, separated by four years, and one with the Very Large Telescope, separated from the second Subaru observation by ∼2 months. We detect 66 narrow absorption lines (NALs), of which 24 are classified as intrinsic NALs that are physically associated with the quasar based on partial coverage analysis. The velocities of intrinsic NALs appear to cluster around values of ${v}_{\mathrm{ej}}$ ∼ 59,000, 43,000, and 29,000 km s⁻¹, which is reminiscent of filamentary structures obtained by numerical simulations. There are no common intrinsic NALs at the same redshift along the two sightlines, implying that the transverse size of the NAL absorbers should be smaller than the sightline distance between two lensed images. In addition to the NALs with large ejection velocities of ${v}_{\mathrm{ej}}$ > 1000 km s⁻¹, we also detect broader proximity absorption lines (PALs) at ${z}_{\mathrm{abs}}$ ∼ ${z}_{\mathrm{em}}$. The PALs are likely to arise in outflowing gas at a distance of r ≤ 620 pc from the central black hole with an electron density of n_e ≥8.7 × 10³ cm⁻³. These limits are based on the assumption that the variability of the lines is due to recombination. We discuss the implications of these results on the three-dimensional structure of the outflow.

We present new theoretical stellar yields and surface abundances for three grids of metal-rich asymptotic giant branch (AGB) models. Post-processing nucleosynthesis results are presented for stellar models with initial masses between 1 M_☉ and 7.5 M_☉ for Z = 0.007, and 1 M_☉ and 8 M_☉ for Z = 0.014 (solar) and Z = 0.03. We include stellar surface abundances as a function of thermal pulse on the AGB for elements from C to Bi and for a selection of isotopic ratios for elements up to Fe and Ni (e.g., ${}^{12}{\rm{C}}$/${}^{13}{\rm{C}}$), which can be obtained from observations of molecules in stars and from the laboratory analysis of meteoritic stardust grains. Ratios of elemental abundances of He/H, C/O, and N/O are also included, which are useful for direct comparison to observations of AGB stars and their progeny, including planetary nebulae. The integrated elemental stellar yields are presented for each model in the grid for hydrogen, helium, and all stable elements from C to Bi. Yields of Li are also included for intermediate-mass models with hot bottom burning. We present the first slow neutron-capture (s-process) yields for super solar metallicity AGB stars with Z = 0.03, and the first complete s-process yields for models more massive than 6 M_☉ at all three metallicities.

We describe a simple image processing technique that is useful for the visualization and depiction of gradually evolving or intermittent structures in solar physics extreme-ultraviolet imagery. The technique is an application of image segmentation, which we call "Persistence Mapping," to isolate extreme values in a data set, and is particularly useful for the problem of capturing phenomena that are evolving in both space and time. While integration or "time-lapse" imaging uses the full sample (of size N ), Persistence Mapping rejects (N − 1)/N of the data set and identifies the most relevant 1/N values using the following rule: if a pixel reaches an extreme value, it retains that value until that value is exceeded. The simplest examples isolate minima and maxima, but any quantile or statistic can be used. This paper demonstrates how the technique has been used to extract the dynamics in long-term evolution of comet tails, erupting material, and EUV dimming regions.

The observed line intensity ratios of the Si iiλ1263 and λ1307 multiplets to that of Si iiλ1814 in the broad-line region (BLR) of quasars are both an order of magnitude larger than the theoretical values. This was first pointed out by Baldwin et al., who termed it the "Si ii disaster," and it has remained unresolved. We investigate the problem in the light of newly published atomic data for Si ii. Specifically, we perform BLR calculations using several different atomic data sets within the CLOUDY modeling code under optically thick quasar cloud conditions. In addition, we test for selective pumping by the source photons or intrinsic galactic reddening as possible causes for the discrepancy, and we also consider blending with other species. However, we find that none of the options investigated resolve the Si ii disaster, with the potential exception of microturbulent velocity broadening and line blending. We find that a larger microturbulent velocity ($\sim 500\;\mathrm{km}\;{{\rm{s}}}^{-1}$) may solve the Si ii disaster through continuum pumping and other effects. The CLOUDY models indicate strong blending of the Si iiλ1307 multiplet with emission lines of O i, although the predicted degree of blending is incompatible with the observed λ1263/λ1307 intensity ratios. Clearly, more work is required on the quasar modeling of not just the Si ii lines but also nearby transitions (in particular those of O i) to fully investigate whether blending may be responsible for the Si ii disaster.

Some recently discovered short-period Earth- to Neptune-sized exoplanets (super-Earths) have low observed mean densities that can only be explained by voluminous gaseous atmospheres. Here, we study the conditions allowing the accretion and retention of such atmospheres. We self-consistently couple the nebular gas accretion onto rocky cores and the subsequent evolution of gas envelopes following the dispersal of the protoplanetary disk. Specifically, we address mass-loss due to both photo-evaporation and cooling of the planet. We find that planets shed their outer layers (dozens of percent in mass) following the disk's dispersal (even without photo-evaporation), and their atmospheres shrink in a few Myr to a thickness comparable to the radius of the underlying rocky core. At this stage, atmospheres containing less particles than the core (equivalently, lighter than a few percent of the planet's mass) can be blown away by heat coming from the cooling core, while heavier atmospheres cool and contract on a timescale of Gyr at most. By relating the mass-loss timescale to the accretion time, we analytically identify a Goldilocks region in the mass-temperature plane in which low-density super-Earths can be found: planets have to be massive and cold enough to accrete and retain their atmospheres, but not too massive or cold, such that they do not enter runaway accretion and become gas giants (Jupiters). We compare our results to the observed super-Earth population and find that low-density planets are indeed concentrated in the theoretically allowed region. Our analytical and intuitive model can be used to investigate possible super-Earth formation scenarios.

The compressibility of molecular cloud (MC) turbulence plays a crucial role in star formation models, because it controls the amplitude and distribution of density fluctuations. The relation between the compressive ratio (the ratio of powers in compressive and solenoidal motions) and the statistics of turbulence has been previously studied systematically only in idealized simulations with random external forces. In this work, we analyze a simulation of large-scale turbulence (250 pc) driven by supernova (SN) explosions that has been shown to yield realistic MC properties. We demonstrate that SN driving results in MC turbulence with a broad lognormal distribution of the compressive ratio, with a mean value ≈0.3, lower than the equilibrium value of ≈0.5 found in the inertial range of isothermal simulations with random solenoidal driving. We also find that the compressibility of the turbulence is not noticeably affected by gravity, nor are the mean cloud radial (expansion or contraction) and solid-body rotation velocities. Furthermore, the clouds follow a general relation between the rms density and the rms Mach number similar to that of supersonic isothermal turbulence, though with a large scatter, and their average gas density probability density function is described well by a lognormal distribution, with the addition of a high-density power-law tail when self-gravity is included.

Deep observations of galaxies reveal faint extended stellar components (hereafter ESCs) of streams, shells, and halos. These are a natural prediction of hierarchical galaxy formation, as accreted satellite galaxies are tidally disrupted by their host. We investigate whether or not global properties of the ESC could be used to test of dark matter, reasoning that they should be sensitive to the abundance of low-mass satellites, and therefore the underlying dark matter model. Using cosmological simulations of galaxy formation in the favored Cold Dark Matter (CDM) and Warm Dark Matter (WDM) models (${m}_{{\rm{WDM}}}=0.5,1,2\;{\rm{keV}}/{c}^{2}$), which suppress the abundance of low-mass satellites, we find that the kinematics and orbital structure of the ESC is consistent across models. However, we find striking differences in its spatial structure, as anticipated—a factor of ∼10 drop in spherically averaged mass density between ∼10% and ∼75% of the virial radius in the more extreme WDM runs (${m}_{{\rm{WDM}}}$ = 0.5, 1 ${\rm{keV}}/{c}^{2}$) relative to the CDM run. These differences are consistent with the mass assembly histories of the different components, and are present across redshifts. However, even the least discrepant of the WDM models is incompatible with current observational limits on ${m}_{{\rm{WDM}}}$. Importantly, the differences we observe when varying the underlying dark matter are comparable to the galaxy-to-galaxy variation we expect within a fixed dark matter model. This suggests that it will be challenging to place limits on dark matter using only the unresolved spatial structure of the the ESC.

Variable emission from Sgr A*, the luminous counterpart to the super-massive black hole at the center of our Galaxy, arises from the innermost portions of the accretion flow. Better characterization of the variability is important for constraining models of the low-luminosity accretion mode powering Sgr A*, and could further our ability to use variable emission as a probe of the strong gravitational potential in the vicinity of the $4\times {10}^{6}{M}_{\odot }$ black hole. We use the Herschel Spectral and Photometric Imaging Receiver (SPIRE) to monitor Sgr A* at wavelengths that are difficult or impossible to observe from the ground. We find highly significant variations at 0.25, 0.35, and 0.5 mm, with temporal structure that is highly correlated across these wavelengths. While the variations correspond to $\lt 1 \%$ changes in the total intensity in the Herschel beam containing Sgr A*, comparison to independent, simultaneous observations at 0.85 mm strongly supports the reality of the variations. The lowest point in the light curves, ∼0.5 Jy below the time-averaged flux density, places a lower bound on the emission of Sgr A* at 0.25 mm, the first such constraint on the THz portion of the spectral energy distribution. The variability on few hour timescales in the SPIRE light curves is similar to that seen in historical 1.3 mm data, where the longest time series is available, but the distribution of variations in the sub-mm do not show a tail of large-amplitude variations seen at 1.3 mm. Simultaneous X-ray photometry from XMM-Newton shows no significant variation within our observing period, which may explain the lack of very large submillimeter variations in our data if X-ray and submillimeter flares are correlated.

We investigate the formation of icy super-Earth mass planets within a gravitationally unstable ring of solids orbiting at 250–750 AU around a 1 ${M}_{\odot }$ star. Coagulation calculations demonstrate that a system of a few large oligarchs and a swarm of pebbles generates a super-Earth within 100–200 Myr at 250 AU and within 1–2 Gyr at 750 AU. Systems with more than ten oligarchs fail to yield super-Earths over the age of the solar system. As these systems evolve, destructive collisions produce detectable debris disks with luminosities of ${10}^{-5}\mbox{--}{10}^{-3}$ relative to the central star.

Using a sample of dwarf irregular galaxies selected from the ALFALFA blind H i-survey and observed using the VIMOS IFU, we investigate the relationship between Hα emission and Balmer optical depth (${\tau }_{{\rm{b}}}$). We find a positive correlation between Hα luminosity surface density and Balmer optical depth in 8 of 11 at ≥0.8σ significance (6 of 11 at ≥1.0σ) galaxies. Our spaxels have physical scales ranging from 30 to 80 pc, demonstrating that the correlation between these two variables continues to hold down to spatial scales as low as 30 pc. Using the Spearman's rank correlation coefficient to test for correlation between ${{\rm{\Sigma }}}_{{\rm{H}}\alpha }$ and ${\tau }_{{\rm{b}}}$ in all the galaxies combined, we find $\rho =0.39$, indicating a positive correlation at 4σ significance. Our low stellar-mass galaxy results are in agreement with observations of emission line regions in larger spiral galaxies, indicating that this relationship is independent of the size of the galaxy hosting the emission line region. The positive correlation between Hα luminosity and Balmer optical depth within spaxels is consistent with the hypothesis that young star-forming regions are surrounded by dusty birth-clouds.

Traditional cosmological inference using Type Ia supernovae (SNe Ia) have used stretch- and color-corrected fits of SN Ia light curves and assumed a resulting fiducial mean and symmetric intrinsic dispersion for the resulting relative luminosity. As systematics become the main contributors to the error budget, it has become imperative to expand supernova cosmology analyses to include a more general likelihood to model systematics to remove biases with losses in precision. To illustrate an example likelihood analysis, we use a simple model of two populations with a relative luminosity shift, independent intrinsic dispersions, and linear redshift evolution of the relative fraction of each population. Treating observationally viable two-population mock data using a one-population model results in an inferred dark energy equation of state parameter w that is biased by roughly 2 times its statistical error for a sample of $N\quad \gtrsim \quad 2500$ SNe Ia. Modeling the two-population data with a two-population model removes this bias at a cost of an approximately $\sim 20 \%$ increase in the statistical constraint on w. These significant biases can be realized even if the support for two underlying SNe Ia populations, in the form of model selection criteria, is inconclusive. With the current observationally estimated difference in the two proposed populations, a sample of $N\quad \gtrsim \quad$ 10,000 SNe Ia is necessary to yield conclusive evidence of two populations.

Recently we discussed an enhancement of the abundance of Ar xiv relative to Ca xiv near a sunspot during a flare, observed in spectra recorded by the Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode spacecraft. The observed Ar xiv/Ca xiv ratio yields an argon/calcium abundance ratio seven times greater than expected from the photospheric abundance. Such a large abundance anomaly is unprecedented in the solar atmosphere. We interpreted this result as being due to an inverse first ionization potential (FIP) effect. In the published work, two lines of Ar xiv were observed, and one line was tentatively identified as an Ar xi line. In this paper, we report observing a similar enhancement in a full-CCD EIS flare spectrum in 13 argon lines that lie within the EIS wavelength ranges. The observed lines include two Ar xi lines, four Ar xiii lines, six Ar xiv lines, and one Ar xv line. The enhancement is far less than reported in Doschek et al. but exhibits similar morphology. The argon abundance is close to a photospheric abundance in the enhanced area, and the abundance could be photospheric. This enhancement occurs in association with a sunspot in a small area only a few arcseconds (1'' = about 700 km) in size. There is no enhancement effect observed in the normally high-FIP sulfur and oxygen line ratios relative to lines of low-FIP elements available to EIS. Calculations of path lengths in the strongest enhanced area in Doschek et al. indicate a depletion of low-FIP elements.

Coronal mass ejections (CMEs) are often accompanied by coronal dimming that is evident in extreme ultraviolet (EUV) and soft X-ray observations. The locations of dimming are sometimes considered to map footpoints of the erupting flux rope. As the emitting material expands in the corona, the decreased plasma density leads to reduced emission observed in spectral and irradiance measurements. Therefore, signatures of dimming may reflect the properties of CMEs in the early phase of their eruption. In this study, we analyze the event of flare, CME, and coronal dimming on 2011 December 26. We use the data from the Atmospheric Imaging Assembly on the Solar Dynamics Observatory for disk observations of the dimming, and analyze images taken by EUVI, COR1, and COR2 on board the Solar Terrestrial Relations Observatory to obtain the height and velocity of the associated CMEs observed at the limb. We also measure the magnetic reconnection rate from flare observations. Dimming occurs in a few locations next to the flare ribbons, and it is observed in multiple EUV passbands. Rapid dimming starts after the onset of fast reconnection and CME acceleration, and its evolution tracks the CME height and flare reconnection. The spatial distribution of dimming exhibits cores of deep dimming with a rapid growth, and their light curves are approximately linearly scaled with the CME height profile. From the dimming analysis we infer the process of the CME expansion, and estimate properties of the CME.

Carbon and oxygen isotopic ratios are reported for a sample of 46 Mira and SRa-type variable asymptotic giant branch (AGB) stars. Vibration–rotation first and second-overtone CO lines in 1.5–2.5 μm spectra were measured to derive isotopic ratios for ¹²C/¹³C, ¹⁶O/¹⁷O, and ¹⁶O/¹⁸O. Comparisons with previous measurements for individual stars and with various samples of evolved stars, as available in the extant literature, are discussed. Models for solar composition AGB stars of different initial masses are used to interpret our results. We find that the majority of M-stars have main sequence masses ≤2 M_⊙ and have not experienced sizable third dredge-up (TDU) episodes. The progenitors of the four S-type stars in our sample are slightly more massive. Of the six C-stars in the sample three have clear evidence relating their origin to the occurrence of TDU. Comparisons with O-rich presolar grains from AGB stars that lived before the formation of the solar system reveal variations in the interstellar medium chemical composition. The present generation of low-mass AGB stars, as represented by our sample of long period variables (LPVs), shows a large spread of ¹⁶O/¹⁷O ratios, similar to that of group 1 presolar grains and in agreement with theoretical expectations for the composition of mass 1.2–2 M_⊙ stars after the first dredge-up. In contrast, the ¹⁶O/¹⁸O ratios of present-day LPVs are definitely smaller than those of group 1 grains. This is most probably a consequence of the the decrease with time of the ¹⁶O/¹⁸O ratio in the interstellar medium due to the chemical evolution of the Milky Way. One star in our sample has an O composition similar to that of group 2 presolar grains originating in an AGB star undergoing extra-mixing. This may indicate that the extra-mixing process is hampered at high metallicity, or, equivalently, favored at low metallicity. Similarly to O-rich grains, no star in our sample shows evidence of hot bottom burning, which is expected for massive AGB stars.

We show that the projected number density profiles of Sloan Digital Sky Survey photometric galaxies around galaxy clusters display strong evidence for the splashback radius, a sharp halo edge corresponding to the location of the first orbital apocenter of satellite galaxies after their infall. We split the clusters into two subsamples with different mean projected radial distances of their members, $\langle {R}_{{\rm{mem}}}\rangle$, at fixed richness and redshift. The sample with smaller $\langle {R}_{{\rm{mem}}}\rangle$ has a smaller ratio of the splashback radius to the traditional halo boundary ${R}_{{\rm{200m}}}$ than the subsample with larger $\langle {R}_{{\rm{mem}}}\rangle$, indicative of different mass accretion rates for these subsamples. The same subsamples were recently used by Miyatake et al. to show that their large-scale clustering differs despite their similar weak lensing masses, demonstrating strong evidence for halo assembly bias. We expand on this result by presenting a 6.6σ difference in the clustering amplitudes of these samples using cluster–photometric galaxy cross-correlations. This measurement is a clear indication that halo clustering depends on parameters other than halo mass. If $\langle {R}_{{\rm{mem}}}\rangle$ is related to the mass assembly history of halos, the measurement is a manifestation of the halo assembly bias. However, our measured splashback radii are smaller, while the strength of the assembly bias signal is stronger, than the predictions of collisionless Λ cold dark matter simulations. We show that dynamical friction, cluster mis-centering, or projection effects are not likely to be the sole source of these discrepancies. However, further investigations regarding unknown catastrophic weak lensing or cluster identification systematics are warranted.

A variety of methods have been proposed to define and to quantify galaxy environments. While these techniques work well in general with spectroscopic redshift samples, their application to photometric redshift surveys remains uncertain. To investigate whether galaxy environments can be robustly measured with photo-z samples, we quantify how the density measured with the nearest-neighbor approach is affected by photo-z uncertainties by using the Durham mock galaxy catalogs in which the 3D real-space environments and the properties of galaxies are known exactly. Furthermore, we present an optimization scheme in the choice of parameters used in the 2D projected measurements that yield the tightest correlation with respect to the 3D real-space environments. By adopting the optimized parameters in the density measurements, we show that the correlation between the 2D projected optimized density and the real-space density can still be revealed, and the color–density relation is also visible out to z ∼ 0.8 even for a photo-z uncertainty (${\sigma }_{{{\rm{\Delta }}}_{z}/(1+z)}$) up to 0.06. We find that at redshifts 0.3 < z < 0.5 a deep (i ∼ 25) photometric redshift survey with ${\sigma }_{{{\rm{\Delta }}}_{z}/(1+z)}\;=\;0.02$ yields a performance in small-scale density measurement that is comparable to a shallower i ∼ 22.5 spectroscopic sample with ∼10% sampling rate. Finally, we discuss the application of the local density measurements to the Pan-STARRS1 Medium Deep Survey (PS-MDS), one of the largest deep optical imaging surveys. Using data from ∼5 square degrees of survey area, our results show that it is possible to measure local density and to probe the color–density relation with 3σ confidence level out to z ∼ 0.8 in the PS-MDS. The color–density relation, however, quickly degrades for data covering smaller areas.

Star-forming galaxies are considered to be the leading candidate sources dominating cosmic reionization at $z\gt 7$: the search for analogs at moderate redshift showing Lyman continuum (LyC) leakage is currently an active line of research. We have observed a star-forming galaxy at z = 3.2 with Hubble/WFC3 in the F336W filter, corresponding to the 730–890 Å rest-frame, and detected LyC emission. This galaxy is very compact and also has a large Oxygen ratio $[{\rm{O}}\;{\rm{III}}]\lambda 5007$/$[{\rm{O}}\;{\rm{II}}]\lambda 3727$ ($\gtrsim 10$). No nuclear activity is revealed from optical/near-infrared spectroscopy and deep multi-band photometry (including the 6 Ms X-ray Chandra observations). The measured escape fraction of ionizing radiation spans the range 50%–100%, depending on the intergalactic medium (IGM) attenuation. The LyC emission is measured at ${m}_{{\rm{F}}336{\rm{W}}}=27.57\pm 0.11$ (with signal-to-noise ratio (S/N) = 10) and is spatially unresolved, with an effective radius of ${R}_{e}\lt 200$ pc. Predictions from photoionization and radiative transfer models are in line with the properties reported here, indicating that stellar winds and supernova explosions in a nucleated star-forming region can blow cavities generating density-bounded conditions compatible to optically thin media. Irrespective of the nature of the ionizing radiation, spectral signatures of these sources over the entire electromagnetic spectrum are of central importance for their identification during the epoch of reionization when the LyC is unobservable. Intriguingly, the Spitzer/IRAC photometric signature of intense rest-frame optical emissions ([O iii]λλ4959,5007 + Hβ) recently observed at $z\simeq 7.5\mbox{--}8.5$ is similar to what is observed in this galaxy. Only the James Webb Space Telescope will measure optical line ratios at $z\gt 7$, allowing a direct comparison with the lower-redshift LyC emitters, such as that reported here.

New near- and far-ultraviolet (NUV and FUV) Hubble Space Telescope spectra of Mrk 231, the nearest quasar known, are combined with ground-based optical spectra to study the remarkable dichotomy between the FUV and NUV–optical spectral regions in this object. The FUV emission-line features are faint, broad, and highly blueshifted (up to ∼7000 km s⁻¹), with no significant accompanying absorption. In contrast, the profiles of the NUV absorption features resemble those of the optical Na i D, He i, and Ca ii H and K lines, exhibiting broad blueshifted troughs that overlap in velocity space with the FUV emission-line features and indicate a dusty, high-density and patchy broad absorption line (BAL) screen covering ∼90% of the observed continuum source at a distance ≲2–20 pc. The FUV continuum emission does not show the presence of any obvious stellar features and is remarkably flat compared with the steeply declining NUV continuum. The NUV (FUV) features and continuum emission have not varied significantly over the past ∼22 (3) years and are unresolved on scales ∼40 (170) pc. These results favor an active galactic nucleus origin for the NUV–FUV line and continuum emission. The observed FUV line emission is produced in the outflowing BAL cloud system, while the Balmer lines arise primarily from the standard broad line region seen through the dusty BAL screen. Our data are inconsistent with the recently proposed binary black hole model. We argue instead that Mrk 231 is the nearest example of weak-lined "wind-dominated" quasars with high Eddington ratios and geometrically thick ("slim") accretion disks; these quasars are likely more common in the early universe.

We investigate the transport of charged particles across magnetic discontinuities, focusing specifically on stream interfaces associated with co-rotating interaction regions in the solar wind. We argue that the magnetic field fluctuations perpendicular to the magnetic discontinuity, and usually also perpendicular to the mean magnetic field, are strongly damped in the vicinity of such a magnetic structure, leading to anisotropic perpendicular diffusion. Assuming that perpendicular diffusion arises from drifts in a turbulent magnetic field, we adopt a simplified approach to derive the relevant perpendicular diffusion coefficient. This approach, which we believe gives the correct principal dependences as expected from more elaborate calculations, allows us to investigate transport in different turbulent geometries, such as longitudinal compressional turbulence that may be present near the heliopause. Although highly dependent on the (possibly anisotropic) perpendicular length scales and turbulence levels, we generally find perpendicular diffusion to be strongly damped at magnetic discontinuities, which may in turn provide an explanation for the large particle gradients associated with these structures.

We present the results of ALMA Cycle 2 observations of the ultraluminous infrared galaxy IRAS 20551−4250 at HCN/HCO⁺/HNC J = 3–2 lines at both vibrational ground (v = 0) and vibrationally excited (v₂ = 1) levels. This galaxy contains a luminous buried active galactic nucleus (AGN), in addition to starburst activity, and our ALMA Cycle 0 data revealed a tentatively detected vibrationally excited HCN v₂ = 1f J = 4–3 emission line. In our ALMA Cycle 2 data, the HCN/HCO⁺/HNC J = 3–2 emission lines at v = 0 are clearly detected. The HCN and HNC v₂ = 1f J = 3–2 emission lines are also detected, but the HCO⁺v₂ = 1f J = 3–2 emission line is not. Given the high energy level of v₂ = 1 and the resulting difficulty of collisional excitation, we compared these results with those of the calculation of infrared radiative pumping, using the available infrared 5–35 μm spectrum. We found that all of the observational results were reproduced if the HCN abundance was significantly higher than that of HCO⁺ and HNC. The flux ratio and excitation temperature between v₂ = 1f and v = 0, after correction for possible line opacity, suggests that infrared radiative pumping affects rotational (J-level) excitation at v = 0 at least for HCN and HNC. The HCN-to-HCO⁺v = 0 flux ratio is higher than those of starburst-dominated regions, and will increase even more when the derived high HCN opacity is corrected. The enhanced HCN-to-HCO⁺ flux ratio in this AGN-hosting galaxy can be explained by the high HCN-to-HCO⁺ abundance ratio and sufficient HCN excitation at up to J = 4, rather than the significantly higher efficiency of infrared radiative pumping for HCN than HCO⁺.

The bright soft X-ray transient Nova Muscae 1991 was intensively observed during its entire eight-month outburst using the Large Area Counter on board the Ginga satellite. Recently, we obtained accurate estimates of the mass of the black hole primary, the orbital inclination angle of the system, and the distance. Using these crucial input data and Ginga X-ray spectra, we have measured the spin of the black hole using the continuum-fitting method. For four X-ray spectra of extraordinary quality we have determined the dimensionless spin parameter of the black hole to be ${a}_{* }={0.63}_{-0.19}^{+0.16}$ (1σ confidence level), a result that we confirm using 11 additional spectra of lower quality. Our spin estimate challenges two published results: it is somewhat higher than the value predicted by a proposed relationship between jet power and spin; and we find that the spin of the black hole is decidedly prograde, not retrograde as has been claimed.

The optical counterpart of the black hole soft X-ray transient Nova Muscae 1991 has brightened by ΔV ≈ 0.8 mag since its return to quiescence 23 yr ago. We present the first clear evidence that the brightening of soft X-ray transients in quiescence occurs at a nearly linear rate. This discovery, and our precise determination of the disk component of emission obtained using our simultaneous photometric and spectroscopic data, has allowed us to identify and accurately model archival ellipsoidal light curves of the highest quality. The simultaneity, and the strong constraint it provides on the component of disk emission, is a key element of our work. Based on our analysis of the light curves, and our earlier measurements of the mass function and mass ratio, we have obtained for Nova Muscae 1991 the first accurate estimates of its systemic inclination $i\;=\;{43.2}_{-2.7}^{+2.1}$ deg, and black hole mass $M\;=\;{11.0}_{-1.4}^{+2.1}\ {M}_{\odot }$. Based on our determination of the radius of the secondary, we estimate the distance to be $D\;=\;{4.95}_{-0.65}^{+0.69}$ kpc. We discuss the implications of our work for future dynamical studies of black hole soft X-ray transients.

Massive black holes at galaxy center may tear apart a star when the star passes occasionally within the disruption radius, which is the so-called tidal disruption event (TDE). Most TDEs radiate with thermal emission resulting from the acceleration disk, but three TDEs have been detected in bright nonthermal X-ray emission, which is interpreted as arising from the relativistic jets. A search for high-energy gamma-ray emission from one relativistic TDE (Swift J164449.3+573451) with the Fermi Large Area Telescope (LAT) has yielded nondetection. In this paper, we report the search for high-energy emission from the other two relativistic TDEs (Swift J2058.4+0516 and Swift J1112.2-8238) during the flare period. No significant GeV emission is found, with an upper limit fluence in the LAT energy range being less than 1% of that in X-rays. Compared with gamma-ray bursts and blazars, these TDEs have the lowest flux ratio between GeV emission and X-ray emission. The nondetection of high-energy emission from relativistic TDEs could be due to the fact that the high-energy emission is absorbed by soft photons in the source. Based on this hypothesis, upper limits on the bulk Lorentz factors, ${\rm{\Gamma }}\lesssim 30$, are then obtained for the jets in these TDEs. We also search for high-energy gamma-ray emission from the nearest TDE discovered to date, ASASSN-14li. No significant GeV emission is found, and an upper limit of $L(0.1\mbox{--}10\;\mathrm{GeV})\leqslant 4.4\times {10}^{42}$ erg s⁻¹ (at 95% confidence level) is obtained for the first 10⁷ s after the disruption.

Reverse shock (RS) emission from gamma-ray bursts is an important tool in investigating the nature of the ejecta from the central engine. If the magnetization of the ejecta is not high enough to suppress the RS, a strong RS emission component, usually peaking in the optical/IR band early on, would provide an important contribution to early afterglow light curve. In the radio band, synchrotron self-absorption may suppress early RS emission and also delay the RS peak time. In this paper, we calculate the self-absorbed RS emission in the radio band under different dynamical conditions. In particular, we stress that the RS radio emission is subject to self-absorption in both RSs and forward shocks (FSs). We calculate the ratio between the RS to FS flux at the RS peak time for different frequencies, which is a measure of the detectability of the RS emission component. We then constrain the range of physical parameters for a detectable RS, in particular the role of magnetization. We notice that unlike optical RS emission which is enhanced by moderate magnetization, moderately magnetized ejecta do not necessarily produce a brighter radio RS due to the self-absorption effect. For typical parameters, the RS emission component would not be detectable below 1 GHz unless the medium density is very low (e.g., n < 10⁻³ cm⁻³ for the interstellar medium and A_* < 5 × 10⁻⁴ for wind). These predictions can be tested using the afterglow observations from current and upcoming radio facilities such as the Karl G. Jansky Very Large Array, the Low-Frequency Array, the Five Hundred Meter Aperture Spherical Telescope, and the Square Kilometer Array.

Large-scale tidal fields estimated directly from the distribution of dark matter halos are used to investigate how halo shapes and spin vectors are aligned with the cosmic web. The major, intermediate, and minor axes of halos are aligned with the corresponding tidal axes, and halo spin axes tend to be parallel with the intermediate axes and perpendicular to the major axes of the tidal field. The strengths of these alignments generally increase with halo mass and redshift, but the dependence is only on the peak height, $\nu \equiv {\delta }_{{\rm{c}}}/\sigma ({M}_{{\rm{h}}},z)$. The scaling relations of the alignment strengths with the value of ν indicate that the alignment strengths remain roughly constant when the structures within which the halos reside are still in a quasi-linear regime, but decreases as nonlinear evolution becomes more important. We also calculate the alignments in projection so that our results can be compared directly with observations. Finally, we investigate the alignments of tidal tensors on large scales, and use the results to understand alignments of halo pairs separated at various distances. Our results suggest that the coherent structure of the tidal field is the underlying reason for the alignments of halos and galaxies seen in numerical simulations and in observations.

Recent supernova (SN) and transient surveys have revealed an increasing number of non-terminal stellar eruptions. Though the progenitor class of these eruptions includes the most luminous stars, little is known of the pre-SN mechanics of massive stars in their most evolved state, thus motivating a census of possible progenitors. From surveys of evolved and unstable luminous star populations in nearby galaxies, we select a sample of yellow and red supergiant (RSG) candidates in M31 and M33 for review of their spectral characteristics and spectral energy distributions (SEDs). Since the position of intermediate- and late-type supergiants on the color–magnitude diagram can be heavily contaminated by foreground dwarfs, we employ spectral classification and multi-band photometry from optical and near-infrared surveys to confirm membership. Based on spectroscopic evidence for mass loss and the presence of circumstellar (CS) dust in their SEDs, we find that 30%–40% of the yellow supergiants are likely in a post-RSG state. Comparison with evolutionary tracks shows that these mass-losing, post-RSGs have initial masses between 20 and 40 M_⊙. More than half of the observed RSGs in M31 and M33 are producing dusty CS ejecta. We also identify two new warm hypergiants in M31, J004621.05+421308.06 and J004051.59+403303.00, both of which are likely in a post-RSG state.

During the planet formation process, billions of comets are created and ejected into interstellar space. The detection and characterization of such interstellar comets (ICs) (also known as extra-solar planetesimals or extra-solar comets) would give us in situ information about the efficiency and properties of planet formation throughout the galaxy. However, no ICs have ever been detected, despite the fact that their hyperbolic orbits would make them readily identifiable as unrelated to the solar system. Moro-Martín et al. have made a detailed and reasonable estimate of the properties of the IC population. We extend their estimates of detectability with a numerical model that allows us to consider "close" ICs, e.g., those that come within the orbit of Jupiter. We include several constraints on a "detectable" object that allow for realistic estimates of the frequency of detections expected from the Large Synoptic Survey Telescope (LSST) and other surveys. The influence of several of the assumed model parameters on the frequency of detections is explored in detail. Based on the expectation from Moro-Martín et al., we expect that LSST will detect 0.001–10 ICs during its nominal 10 year lifetime, with most of the uncertainty from the unknown number density of small (nuclei of ∼0.1–1 km) ICs. Both asteroid and comet cases are considered, where the latter includes various empirical prescriptions of brightening. Using simulated LSST-like astrometric data, we study the problem of orbit determination for these bodies, finding that LSST could identify their orbits as hyperbolic and determine an ephemeris sufficiently accurate for follow-up in about 4–7 days. We give the hyperbolic orbital parameters of the most detectable ICs. Taking the results into consideration, we give recommendations to future searches for ICs.

Black hole–neutron star (BH–NS) mergers are among the most promising gravitational-wave sources for ground-based detectors, and gravitational waves from BH–NS mergers are expected to be detected in the next few years. The simultaneous detection of electromagnetic counterparts with gravitational waves would provide rich information about merger events. Among the possible electromagnetic counterparts from BH–NS mergers is the so-called kilonova/macronova, emission powered by the decay of radioactive r-process nuclei, which is one of the best targets for follow-up observations. We derive fitting formulas for the mass and the velocity of ejecta from a generic BH–NS merger based on recently performed numerical-relativity simulations. We combine these fitting formulas with a new semi-analytic model for a BH–NS kilonova/macronova lightcurve, which reproduces the results of radiation-transfer simulations. Specifically, the semi-analytic model reproduces the results of each band magnitude obtained by the previous radiation-transfer simulations within ∼1 mag. By using this semi-analytic model we found that, at 400 Mpc, the kilonova/macronova is as bright as 22–24 mag for cases with a small chirp mass and a high black hole spin, and >28 mag for a large chirp mass and a low black hole spin. We also apply our model to GRB 130603B as an illustration, and show that a BH–NS merger with a rapidly spinning black hole and a large neutron star radius is favored.

We report on the detection and early characterization of a hot Jupiter in a three day orbit around K2-34 (EPIC 212110888), a metal-rich F-type star located in the K2 Cycle 5 field. Our follow-up campaign involves precise radial velocity (RV) measurements and high-contrast imaging using multiple facilities. The absence of a bright nearby source in our high-contrast data suggests that the transit-like signals are not due to light variations from such a companion star. Our intensive RV measurements show that K2-34b (EPIC 212110888b) has a mass of $1.773\pm 0.086{M}_{J}$, confirming its status as a planet. We also detect the Rossiter–McLaughlin effect for K2-34b and show that the system has a good spin–orbit alignment ($\lambda \;=\;-{1}_{-9}^{+10}$ degrees). High-contrast images obtained by the HiCIAO camera on the Subaru 8.2 m telescope reveal a faint companion candidate (CC) (${\rm{\Delta }}{m}_{H}\;=\;6.19\pm 0.11$ mag) at a separation of $0\buildrel{\prime\prime}\over{.} 36$. Follow-up observations are needed to confirm that the CC is physically associated with K2-34. K2-34b appears to be an example of a typical "hot Jupiter," albeit one which can be precisely characterized using a combination of K2 photometry and ground-based follow-up.

In this paper we present the results of a mid-infrared study of G49.5-0.4, or W51A, part of the massive starbirth complex W51. Combining public data from the Spitzer IRAC camera, and Gemini mid-infrared camera T-ReCS at 7.73, 9.69, 12.33, and 24.56 μm, with a spatial resolution of ∼05, we have identified the mid-infrared counterparts of eight ultracompact H ii regions, showing that two radio sources are deeply embedded in molecular clouds and another is a cloud of ionized gas. From the T-ReCS data we have unveiled the central core of the W51 region, revealing massive young stellar candidates. We modeled the spectral energy distribution of the detected sources. The results suggest that the embedded objects are sources with spectral types ranging from B3 to O5, but the majority of the fits indicate stellar objects with B1 spectral types. We also present an extinction map of IRS 2, showing that a region with lower extinction corresponds to the region where a proposed jet of gas has impacted the foreground cloud. From this map, we also derived the total extinction toward the enigmatic source IRS 2E, which amounts to ∼60 mag in the V band. We calculated the color temperature due to thermal emission of the circumstellar dust of the detected sources; the temperatures are in the interval of ∼100–150 K, which corresponds to the emission of dust located at 0.1 pc from the central source. Finally, we show a possible mid-infrared counterpart of a detected source at millimeter wavelengths that was found by Zapata et al. to be a massive young stellar object undergoing a high accretion rate.

It has been proposed that particles bouncing between magnetized flows converging in a reconnection region can be accelerated by the first-order Fermi mechanism. Analytical considerations of this mechanism have shown that the spectral index of accelerated particles is related to the total plasma compression within the reconnection region, similarly to the case of the diffusive shock acceleration mechanism. As a first step to investigate the efficiency of Fermi acceleration in reconnection regions in producing hard energy spectra of particles in the solar corona, we explore the degree of plasma compression that can be achieved at reconnection sites. In particular, we aim to determine the conditions for the strong compressions to form. Using a two-dimensional resistive MHD numerical model, we consider a set of magnetic field configurations where magnetic reconnection can occur, including a Harris current sheet, a force-free current sheet, and two merging flux ropes. Plasma parameters are taken to be characteristic of the solar corona. Numerical simulations show that strong plasma compressions (≥4) in the reconnection regions can form when the plasma heating due to reconnection is efficiently removed by fast thermal conduction or the radiative cooling process. The radiative cooling process that is negligible in the typical 1 MK corona can play an important role in the low corona/transition region. It is found that plasma compression is expected to be strongest in low-beta plasma β ∼ 0.01–0.07 at reconnection magnetic nulls.

Fluxes emitted at different wavebands from active galactic nuclei (AGNs) fluctuate at both long and short timescales. The variation can typically be characterized by a broadband power spectrum, which exhibits a red-noise process at high frequencies. The standard method of estimating the power spectral density (PSD) of AGN variability is easily affected by systematic biases such as red-noise leakage and aliasing, in particular when the observation spans a relatively short period and is gapped. Focusing on the high-frequency PSD that is strongly distorted due to red-noise leakage and usually not significantly affected by aliasing, we develop a novel and observable normalized leakage spectrum (NLS), which sensitively describes the effects of leaked red-noise power on the PSD at different temporal frequencies. Using Monte Carlo simulations, we demonstrate how an AGN underlying PSD sensitively determines the NLS when there is severe red-noise leakage, and thereby how the NLS can be used to effectively constrain the underlying PSD.

When a Type Ia supernova (SN Ia) progenitor first ignites carbon in its core, it undergoes ∼10³–10⁴ years of convective burning prior to the onset of thermonuclear runaway. This carbon simmering phase is important for setting the thermal profile and composition of the white dwarf. Using the MESA stellar evolution code, we follow this convective burning and examine the production of neutron-rich isotopes. The neutron content of the SN fuel has important consequences for the ensuing nucleosynthesis, and in particular, for the production of secondary Fe-peak nuclei like Mn and stable Ni. These elements have been observed in the X-ray spectra of SN remnants like Tycho, Kepler, and 3C 397, and their yields can provide valuable insights into the physics of SNe Ia and the properties of their progenitors. We find that weak reactions during simmering can at most generate a neutron excess of ≈ 3 × 10⁻⁴. This is ≈ 70% lower than that found in previous studies that do not take the full density and temperature profile of the simmering region into account. Our results imply that the progenitor metallicity is the main contributor to the neutron excess in SN Ia fuel for Z ≳ 1/3 Z_⊙. Alternatively, at lower metallicities, this neutron excess provides a floor that should be present in any centrally-ignited SN Ia scenario.

Quasi-periodic disturbances of emission-line parameters are frequently observed in the corona. These disturbances propagate upward along the magnetic field with speeds of ∼100 km s⁻¹. This phenomenon has been interpreted as evidence of the propagation of slow magnetosonic waves or has been argued to be a signature of intermittent outflows superposed on the background plasmas. Here we aim to present a new "wave + flow" model to interpret these observations. In our scenario, the oscillatory motion is a slow-mode wave, and the flow is associated with a beam created by the wave–particle interaction owing to Landau resonance. With the help of a kinetic model, we simulate the propagation of slow-mode waves and the generation of beam flows. We find that weak periodic beam flows can be generated by to Landau resonance in the solar corona, and the phase with the strongest blueward asymmetry is ahead of that with the strongest blueshift by about 1/4 period. We also find that the slow wave damps to the level of 1/e after the transit time of two wave periods, owing to Landau damping and Coulomb collisions in our simulation. This damping timescale is similar to that resulting from thermal conduction in the MHD regime. The beam flow is weakened/attenuated with increasing wave period and decreasing wave amplitude since Coulomb collisions become more and more dominant over the wave action. We suggest that this "wave + flow" kinetic model provides an alternative explanation for the observed quasi-periodic propagating perturbations in various parameters in the solar corona.

We present a broadband polarization analysis of 36 discrete polarized radio sources over a very broad, densely sampled frequency band. Our sample was selected on the basis of polarization behavior apparent in narrowband archival data at 1.4 GHz: half the sample shows complicated frequency-dependent polarization behavior (i.e., Faraday complexity) at these frequencies, while half shows comparatively simple behavior (i.e., they appear Faraday simple). We re-observed the sample using the Australia Telescope Compact Array in full polarization, with 6 GHz of densely sampled frequency coverage spanning 1.3–10 GHz. We have devised a general polarization modeling technique that allows us to identify multiple polarized emission components in a source, and to characterize their properties. We detect Faraday complex behavior in almost every source in our sample. Several sources exhibit particularly remarkable polarization behavior. By comparing our new and archival data, we have identified temporal variability in the broadband integrated polarization spectra of some sources. In a number of cases, the characteristics of the polarized emission components, including the range of Faraday depths over which they emit, their temporal variability, spectral index, and the linear extent of the source, allow us to argue that the spectropolarimetric data encode information about the magneto-ionic environment of active galactic nuclei themselves. Furthermore, the data place direct constraints on the geometry and magneto-ionic structure of this material. We discuss the consequences of restricted frequency bands on the detection and interpretation of polarization structures, and the implications for upcoming spectropolarimetric surveys.

We report on the mass and distance measurements of two single-lens events from the 2015 Spitzer microlensing campaign. With both finite-source effect and microlens parallax measurements, we find that the lens of OGLE-2015-BLG-1268 is very likely a brown dwarf (BD). Assuming that the source star lies behind the same amount of dust as the Bulge red clump, we find the lens is a 45 ± 7 ${M}_{{\rm{J}}}$ BD at 5.9 ± 1.0 kpc. The lens of of the second event, OGLE-2015-BLG-0763, is a 0.50 ± 0.04 ${M}_{\odot }$ star at 6.9 ± 1.0 kpc. We show that the probability to definitively measure the mass of isolated microlenses is dramatically increased once simultaneous ground- and space-based observations are conducted.

Weak gravitational lensing causes subtle changes in the apparent shapes of galaxies due to the bending of light by the gravity of foreground masses. By measuring the shapes of large numbers of galaxies (millions in recent surveys, up to tens of billions in future surveys) we can infer the parameters that determine cosmology. Imperfections in the detectors used to record images of the sky can introduce changes in the apparent shapes of galaxies, which in turn can bias the inferred cosmological parameters. In this paper we consider the effect of two widely discussed sensor imperfections: tree rings, due to impurity gradients that cause transverse electric fields in the charge-coupled devices (CCDs), and pixel size variation, due to periodic CCD fabrication errors. These imperfections can be observed when the detectors are subject to uniform illumination (flat-field images). We develop methods to determine the spurious shear and convergence (due to the imperfections) from the flat-field images. We calculate how the spurious shear when added to the lensing shear will bias the determination of cosmological parameters. We apply our methods to candidate sensors of the Large Synoptic Survey Telescope (LSST) as a timely and important example, analyzing flat-field images recorded with LSST prototype CCDs in the laboratory. We find that tree rings and periodic pixel size variation present in the LSST CCDs will introduce negligible bias to cosmological parameters determined from the lensing power spectrum, specifically w, ${{\rm{\Omega }}}_{m}$, and ${\sigma }_{8}$.

The origin of Jupiter-mass planets with orbital periods of only a few days is still uncertain. It is widely believed that these planets formed near the water–ice line of the protoplanetary disk, and subsequently migrated into much smaller orbits. Most of the proposed migration mechanisms can be classified either as disk-driven migration, or as excitation of a very high eccentricity followed by tidal circularization. In the latter scenario, the giant planet that is destined to become a hot Jupiter spends billions of years on a highly eccentric orbit, with apastron near the water–ice line. Eventually, tidal dissipation at periastron shrinks and circularizes the orbit. If this is correct, then it should be especially rare for hot Jupiters to be accompanied by another giant planet interior to the water–ice line. Using the current sample of giant planets discovered with the Doppler technique, we find that hot Jupiters with P_orb < 10 days are no more or less likely to have exterior Jupiter-mass companions than longer-period giant planets with P_orb ≥ 10 days. This result holds for exterior companions both inside and outside of the approximate location of the water–ice line. These results are difficult to reconcile with the high-eccentricity migration scenario for hot Jupiter formation.

This paper examines the standard model of planet formation, including pebble accretion, using numerical simulations. Planetary embryos that are large enough to become giant planets do not form beyond the ice line within a typical disk lifetime unless icy pebbles stick at higher speeds than in experiments using rocky pebbles. Systems like the solar system (small inner planets and giant outer planets) can form if icy pebbles are stickier than rocky pebbles, and if the planetesimal formation efficiency increases with pebble size, which prevents the formation of massive terrestrial planets. Growth beyond the ice line is dominated by pebble accretion. Most growth occurs early, when the surface density of the pebbles is high due to inward drift of the pebbles from the outer disk. Growth is much slower after the outer disk is depleted. The outcome is sensitive to the disk radius and turbulence level, which control the lifetime and maximum size of pebbles. The outcome is sensitive to the size of the largest planetesimals because there is a threshold mass for the onset of pebble accretion. The planetesimal formation rate is unimportant, provided that some large planetesimals form while the pebbles remain abundant. Two outcomes are seen, depending on whether pebble accretion begins while the pebbles are still abundant. Either multiple gas-giant planets form beyond the ice line, small planets form close to the star, and a Kuiper-belt-like disk of bodies is scattered outward by the giant planets; or no giants form and the bodies remain an Earth-mass or smaller.

In a recent paper, Smith & Tombleson state that the luminous blue variables (LBVs) in the Milky Way and the Magellanic Clouds are isolated; they are not spatially associated with young O-type stars. They propose a novel explanation that would overturn the standard view of LBVs. In this paper we test their hypothesis for the LBVs in M31 and M33, as well as the LMC and SMC. We show that in M31 and M33 the LBVs are associated with luminous young stars and supergiants that are appropriate to their luminosities and positions on the H-R diagram. Moreover, in the Smith and Tombleson scenario most of the LBVs should be runaway stars, but the stars' velocities are consistent with their positions in the respective galaxies. In the Magellanic Clouds, those authors' sample was a mixed population. We reassess their analysis, removing seven stars that have no clear relation to LBVs. When we separate the more massive classical and the less luminous LBVs, the classical LBVs have a distribution similar to the late O-type stars, while the less luminous LBVs have a distribution like the red supergiants. None of the confirmed LBVs have high velocities or are candidate runaway stars. These results support the accepted description of LBVs as evolved massive stars that have shed a lot of mass and are now close to their Eddington limit.

We report the detection of large variations in the outflow wind velocity from a young eruptive star, V899 Mon, during its ongoing high accretion outburst phase. Such large variations in the outflow velocity (from −722 to −425 km s⁻¹) have never been reported previously in this family of objects. Our continuous monitoring of this source shows that the multi-component, clumpy, and episodic high velocity outflows are stable in the timescale of a few days, and vary over the timescale of a few weeks to months. We detect significant decoupling in the instantaneous outflow strength to accretion rate. From the comparison of various possible outflow mechanisms in magnetospheric accretion of young stellar objects, we conclude magnetically driven polar winds to be the most consistent mechanism for the outflows seen in V899 Mon. The large scale fluctuations in outflow over the short period makes V899 Mon the most ideal source to constrain various magnetohydrodynamics simulations of magnetospheric accretion.

A linear polarization field on the sphere can be uniquely decomposed into an E-mode and a B-mode component. These two components are analytically defined in terms of spin-2 spherical harmonics. Maps that contain filtered modes on a partial sky can also be decomposed into E-mode and B-mode components. However, the lack of full sky information prevents orthogonally separating these components using spherical harmonics. In this paper, we present a technique for decomposing an incomplete map into E and B-mode components using E and B eigenmodes of the pixel covariance in the observed map. This method is found to orthogonally define E and B in the presence of both partial sky coverage and spatial filtering. This method has been applied to the Bicep2 and the Keck Array maps and results in reducing E to B leakage from ΛCDM E-modes to a level corresponding to a tensor-to-scalar ratio of $r\lt 1\times {10}^{-4}$.

Substantial evidence points to dusty, geometrically thick tori obscuring the central engines of active galactic nuclei (AGNs), but so far no mechanism satisfactorily explains why cool dust in the torus remains in a puffy geometry. Near-Eddington infrared (IR) and ultraviolet (UV) luminosities coupled with high dust opacities at these frequencies suggest that radiation pressure on dust can play a significant role in shaping the torus. To explore the possible effects of radiation pressure, we perform three-dimensional radiative hydrodynamics simulations of an initially smooth torus. Our code solves the hydrodynamics equations, the time-dependent multi–angle group IR radiative transfer (RT) equation, and the time-independent UV RT equation. We find a highly dynamic situation. IR radiation is anisotropic, leaving primarily through the central hole. The torus inner surface exhibits a break in axisymmetry under the influence of radiation and differential rotation; clumping follows. In addition, UV radiation pressure on dust launches a strong wind along the inner surface; when scaled to realistic AGN parameters, this outflow travels at $\sim 5000\;{(M/{10}^{7}{M}_{\odot })}^{1/4}$${[{L}_{\mathrm{UV}}/(0.1{L}_{{\rm{E}}})]}^{1/4}\;\mathrm{km}\;{{\rm{s}}}^{-1}$ and carries $\sim 0.1\;{(M/{10}^{7}{M}_{\odot })}^{3/4}$${[{L}_{\mathrm{UV}}/(0.1{L}_{{\rm{E}}})]}^{3/4}\;$M_⊙ yr⁻¹, where M, ${L}_{\mathrm{UV}}$, and ${L}_{{\rm{E}}}$ are the mass, UV luminosity, and Eddington luminosity of the central object respectively.

Over two decades ago, a prominent, mysterious emission band peaking at ∼20.1 μm was serendipitously detected in four preplanetary nebulae (PPNe; also known as "protoplanetary nebulae"). To date, this spectral feature, designated as the "21 μm" feature, has been seen in 27 carbon-rich PPNe in the Milky Way and the Magellanic Clouds. The nature of its carriers remains unknown although many candidate materials have been proposed. The 21 μm sources also exhibit an equally mysterious, unidentified emission feature peaking at 30 μm. While the 21 μm feature is exclusively seen in PPNe, a short-lived evolutionary stage between the end of the asymptotic giant branch (AGB) and planetary nebula (PN) phases, the 30 μm feature is more commonly observed in all stages of stellar evolution from the AGB through PPN to PN phases. We derive the stellar mass-loss rates ($\dot{M}$) of these sources from their infrared (IR) emission, using the "2-DUST" radiative transfer code for axisymmetric dusty systems which allows one to distinguish the mass-loss rates of the AGB phase (${\dot{M}}_{\mathrm{AGB}}$) from that of the superwind (${\dot{M}}_{\mathrm{SW}}$) phase. We examine the correlation between ${\dot{M}}_{\mathrm{AGB}}$ or ${\dot{M}}_{\mathrm{SW}}$ and the fluxes emitted from the 21 and 30 μm features. We find that both features tend to correlate with ${\dot{M}}_{\mathrm{AGB}}$, suggesting that their carriers are probably formed in the AGB phase. The nondetection of the 21 μm feature in AGB stars suggests that, unlike the 30 μm feature, the excitation of the carriers of the 21 μm feature may require ultraviolet photons which are available in PPNe but not in AGB stars.

Nearly one-third of the sources listed in the Third Fermi Large Area Telescope (LAT) catalog (3FGL) remain unassociated. It is possible that predicted and even unanticipated gamma-ray source classes are present in these data waiting to be discovered. Taking advantage of the excellent spectral capabilities achieved by the Fermi LAT, we use machine-learning classifiers (Random Forest and XGBoost) to pinpoint potentially novel source classes in the unassociated 3FGL sample outside the Galactic plane. Here we report a total of 34 high-confidence Galactic candidates at $| b| \geqslant 5^\circ$. The currently favored standard astrophysical interpretations for these objects are pulsars or low-luminosity globular clusters hosting millisecond pulsars (MSPs). Yet these objects could also be interpreted as dark matter annihilation taking place in ultra-faint dwarf galaxies or dark matter subhalos. Unfortunately, Fermi LAT spectra are not sufficient to break degeneracies between the different scenarios. Careful visual inspection of archival optical images reveals no obvious evidence for low-luminosity globular clusters or ultra-faint dwarf galaxies inside the 95% error ellipses. If these are pulsars, this would bring the total number of MSPs at $| b| \geqslant 5^\circ$ to 106, down to an energy flux ≈4.0 × 10⁻¹² erg cm⁻² s⁻¹ between 100 MeV and 100 GeV. We find this number to be in excellent agreement with predictions from a new population synthesis of MSPs that predicts 100–126 high-latitude 3FGL MSPs depending on the choice of high-energy emission model. If, however, these are dark matter substructures, we can place upper limits on the number of Galactic subhalos surviving today and on dark matter annihilation cross sections. These limits are beginning to approach the canonical thermal relic cross section for dark matter particle masses below ∼100 GeV in the bottom quark ($b\bar{b}$) annihilation channel.

Observations reveal that mass-transferring binary systems may have non-zero orbital eccentricities. The time evolution of the orbital semimajor axis and eccentricity of mass-transferring eccentric binary systems is an important part of binary evolution theory and has been widely studied. However, various different approaches to and assumptions on the subject have made the literature difficult to comprehend and comparisons between different orbital element time evolution equations not easy to make. Consequently, no self-consistent treatment of this phase has ever been included in binary population synthesis codes. In this paper, we present a general formalism to derive the time evolution equations of the binary orbital elements, treating mass loss and mass transfer as perturbations of the general two-body problem. We present the self-consistent form of the perturbing acceleration and phase-dependent time evolution equations for the orbital elements under different mass loss/transfer processes. First, we study the cases of isotropic and anisotropic wind mass loss. Then, we proceed with non-isotropic ejection and accretion in a conservative as well as a non-conservative manner for both point masses and extended bodies. We compare the derived equations with similar work in the literature and explain the existing discrepancies.

Finite eccentricities in mass-transferring eccentric binary systems can be explained by taking into account the mass loss and mass transfer processes that often occur in these systems. These processes can be treated as perturbations of the general two-body problem. The time-evolution equations for the semimajor axis and the eccentricity derived from perturbative methods are generally phase-dependent. The osculating semimajor axis and eccentricity change over the orbital timescale and are not easy to implement in binary evolution codes like MESA. However, the secular orbital element evolution equations can be simplified by averaging over the rapidly varying true anomalies. In this paper, we derive the secular time-evolution equations for the semimajor axis and the eccentricity for various mass loss/transfer processes using either the adiabatic approximation or the assumption of delta-function mass loss/transfer at periastron. We begin with the cases of isotropic and anisotropic wind mass loss. We continue with conservative and non-conservative non-isotropic mass ejection/accretion (including Roche-Lobe-Overflow) for both point-masses and extended bodies. We conclude with the case of phase-dependent mass accretion. Comparison of the derived equations with similar work in the literature is included and an explanation of the existing discrepancies is provided.

We present a detailed, multi-wavelength study of star formation (SF) and active galactic nucleus (AGN) activity in 11 near-infrared (IR) selected, spectroscopically confirmed massive (≳10¹⁴M_⊙) galaxy clusters at 1 < z < 1.75. Using new deep Herschel/PACS imaging, we characterize the optical to far-IR spectral energy distributions (SEDs) for IR-luminous cluster galaxies, finding that they can, on average, be well described by field galaxy templates. Identification and decomposition of AGNs through SED fittings allows us to include the contribution to cluster SF from AGN host galaxies. We quantify the star-forming fraction, dust-obscured SF rates (SFRs) and specific SFRs for cluster galaxies as a function of cluster-centric radius and redshift. In good agreement with previous studies, we find that SF in cluster galaxies at z ≳ 1.4 is largely consistent with field galaxies at similar epochs, indicating an era before significant quenching in the cluster cores (r < 0.5 Mpc). This is followed by a transition to lower SF activity as environmental quenching dominates by z ∼ 1. Enhanced SFRs are found in lower mass ($10.1\lt \mathrm{log}\;{M}_{\star }/{M}_{\odot }\lt 10.8$) cluster galaxies. We find significant variation in SF from cluster to cluster within our uniformly selected sample, indicating that caution should be taken when evaluating individual clusters. We examine AGNs in clusters from z = 0.5–2, finding an excess AGN fraction at z ≳ 1, suggesting environmental triggering of AGNs during this epoch. We argue that our results—a transition from field-like to quenched SF, enhanced SF in lower mass galaxies in the cluster cores, and excess AGNs—are consistent with a co-evolution between SF and AGNs in clusters and an increased merger rate in massive halos at high redshift.

We present a statistical analysis of the accuracy of the digitized magnitudes of photometric plates on the timescale of decades. In our examination of archival Johnson B photometry from the Harvard DASCH archive, we find a median rms scatter of light curves of the order of 0.15 mag over the range B ∼ 9–17 for all calibrations. Slight underlying systematics (trends or flux discontinuities) are on a level of ≲0.2 mag per century (1889–1990) for the majority of constant stars. These historic data can be unambiguously used for processes that happen on scales of magnitudes, and need to be carefully examined in cases approaching the noise floor. The characterization of these limits in photometric stability may guide future studies in their use of plate archives. We explain these limitations for the example case of KIC 8462852, which has been claimed to dim by 0.16 mag per century, and show that this trend cannot be considered as significant.

We present a multi-wavelength study of four high redshift blazars, S5 0014+81 (z = 3.37), CGRaBS J0225+1846 (z = 2.69), BZQ J1430+4205 (z = 4.72), and 3FGL J1656.2−3303 (z = 2.40) using quasi-simultaneous data from the Swift, Nuclear Spectroscopic Telescope Array (NuSTAR) and the Fermi-Large Area Telescope (LAT) and also archival XMM-Newton observations. Other than 3FGL J1656.2−3303, none of the sources were known as γ-ray emitters, and our analysis of ∼7.5 yr of LAT data reveals the first time detection of statistically significant γ-ray emission from CGRaBS J0225+1846. We generate the broadband spectral energy distributions (SED) of all the objects, centering at the epoch of NuSTAR observations and reproduce them using a one-zone leptonic emission model. The optical−UV emission in all the objects can be explained by radiation from the accretion disk, whereas the X-ray to γ-ray windows of the SEDs are found to be dominated by inverse Compton scattering off the broad line region photons. All of them host black holes that are billions of solar masses. Comparing the accretion disk luminosity and the jet power of these sources with a large sample of blazars, we find them to occupy a high disk luminosity–jet power regime. We also investigate the X-ray spectral properties of the sources in detail with a major focus on studying the causes of soft X-ray deficit, a feature generally seen in high redshift radio-loud quasars. We summarize that this feature could be explained based on the intrinsic curvature in the jet emission rather than being due to the external effects predicted in earlier studies, such as host galaxy and/or warm absorption.

We studied the variations of line of sight photospheric plasma flows during the formation phase of the penumbra around a pore in active region NOAA 11490. We used a high spatial, spectral, and temporal resolution data set acquired by the Interferometric BIdimensional Spectrometer operating at the NSO/Dunn Solar Telescope as well as data taken by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory satellite (SDO/HMI). Before the penumbra formed we observed a redshift of the spectral line in the inner part of the annular zone surrounding the pore as well as a blueshift of material associated with opposite magnetic polarity farther away from the pore. We found that the onset of the classical Evershed flow occurs on a very short timescale (1 to 3 hr) while the penumbra is forming. During the same time interval we found changes in the magnetic field inclination in the penumbra, with the vertical field actually changing sign near the penumbral edge, while the total magnetic field showed a significant increase, about 400 G. To explain these and other observations related to the formation of the penumbra and the onset of the Evershed flow we propose a scenario in which the penumbra is formed by magnetic flux dragged down from the canopy surrounding the initial pore. The Evershed flow starts when the sinking magnetic field dips below the solar surface and magnetoconvection sets in.

Gaia is leading us into a new era with a high astrometry precision of ∼10 μas. Under such precision, astrometry can play an important role in detecting and characterizing exoplanets. In particular, we can identify planet pairs in mean motion resonances (MMRs), which constrain the formation and evolution of planetary systems. In accordance with observations, we consider two-Jupiter or two-super-Earth systems in 1:2, 2:3, and 3:4 MMRs. Our simulations show that the false alarm probabilities (FAPs) of a third planet are extremely small, while the two real planets can be fitted well with a signal-to-noise ratio (S/N)$\;\gt \;3$. The probability of reconstructing a resonant system is related to the eccentricities and the resonance intensity. Generally, when the S/N $\geqslant \;10$, if the eccentricities of both planets are larger than 0.01 and the resonance is quite strong, the probability of reconstructing the planet pair in MMRs is $\geqslant \;80 \%$. Jupiter pairs in MMRs are reconstructed more easily than super-Earth pairs with similar S/N when we consider dynamical stability. FAPs are also calculated when we detect planet pairs in or near MMRs. The FAPs for 1:2 MMRs are the largest, i.e., FAP $\gt 15 \%$ when S/N $\leqslant \;10$. Extrapolating from the Kepler planet pairs near MMRs and assuming a S/N ∼ 3, we discover and reconstruct a few tens of Jupiter pairs and hundreds of super-Earth pairs in 2:3 and 1:2 MMRs within 30 pc. We also compare the differences between even and uneven data cadence and find that planets are better measured with more uniform phase coverage.

Transitional disks, protoplanetary disks with deep and wide central gaps, may be the result of planetary sculpting. By comparing numerical planet-opening-gap models with observed gaps, we find systems of 3–6 giant planets are needed in order to open gaps with the observed depths and widths. We explore the dynamical stability of such multi-planet systems using N-body simulations that incorporate prescriptions for gas effects. We find they can be stable over a typical disk lifetime, with the help of eccentricity damping from the residual gap gas that facilitates planets locking into mean motion resonances. However, in order to account for the occurrence rate of transitional disks, the planet sculpting scenario demands gap-opening-friendly disk conditions, in particular, a disk viscosity α ≲ 0.001. In addition, the demography of giant planets at ∼3–30 au separations, poorly constrained by current data, has to largely follow occurrence rates extrapolated outward from radial velocity surveys, not the lower occurrence rates extrapolated inward from direct imaging surveys. Even with the most optimistic occurrence rates, transitional disks cannot be a common phase that most gas disks experience at the end of their life, as popularly assumed, simply because there are not enough planets to open these gaps. Finally, as consequences of demanding almost all giant planets at large separations participate in transitional disk sculpting, the majority of such planets must form early and end up in a chain of mean motion resonances at the end of disk lifetime.

To understand the evolution and the habitability of any rocky exoplanet demands detailed knowledge about its geophysical state and history—such as predicting the tectonic mode of a planet. Yet no astronomical observation can directly confirm or rule out the occurrence of plate tectonics on a given exoplanet. Moreover, the field of plate tectonics is still young—questioning whether we should study plate tectonics on exoplanets at this point in time. In this work, we determine the limitations and the emerging possibilities of exogeophysics, the science of connecting geophysics to exoplanets, on the example of plate tectonics. Assuming current uncertainties in model and planet parameters, we develop a qualitatively probabilistic and conservative framework to estimate on what kind of planets and where in the Galaxy plate tectonics might occur. This we achieve by modeling how plate yielding, the most critical condition needed for plate mobility and subduction, is affected by directly observable (planet mass, size) or indirectly, to some degree, assessable planet properties (structure and composition). Our framework not only highlights the importance of a planet's chemistry for the existence of plate tectonics and the path toward practical exogeophysics but also demonstrates how exoplanet science can actually help to better understand geophysics and the fundamentals of plate tectonics on Earth itself.

We conducted survey observations of a glycine precursor, methanimine, or methylenimine (CH₂NH), with the Nobeyama Radio Observatory 45 m telescope and the Sub-Millimeter Radio telescope toward 12 high-mass and two low-mass star-forming regions in order to increase the number of known CH₂NH sources and to better understand the characteristics of CH₂NH sources. As a result of our survey, CH₂NH was detected in eight sources, including four new sources. The estimated fractional abundances were ∼10⁻⁸ in Orion KL and G10.47+0.03, while they were ∼10⁻⁹ toward the other sources. Our hydrogen recombination line and past studies suggest that CH₂NH-rich sources have less (this mean not so evolved) evolved H ii regions. The lower destruction rates from UV flux from the central star would contribute to the high CH₂NH abundances toward CH₂NH-rich sources. Our gas-grain chemical simulations suggest that CH₂NH is mostly formed in the gas phase by neutral–neutral reactions, rather than being the product of thermal evaporation from dust surfaces.

In the catalog of M-dwarfs presented in Holwerda et al. (2014, H14 hereafter), there is an issue with the conversion from celestial coordinates to Galactic ones, done with pyephem a wrapper around a trusted and vetted library ephermis. Here we present the corrected coordinates (using AstroPy) and distances based on AB magnitudes. We have amended the tables and figures accordingly. The relation between vertical scale-height (z₀) and M- dwarf subtype found in H14 is no longer present. We find a scale-height of 600 pc for all types, in part due to the presence of a second Galactic structural component.