The 100 most-cited articles in The Astrophysical Journal, 2016

ABSTRACT This is the first of a series of papers presenting the Modules for Experiments in Stellar Astrophysics (MESA) Isochrones and Stellar Tracks (MIST) project, a new comprehensive set of stellar evolutionary tracks and isochrones computed using MESA, a state-of-the-art open-source 1D stellar evolution package. In this work, we present models with solar-scaled abundance ratios covering a wide range of ages ( ), masses ( ), and metallicities ( ). The models are self-consistently and continuously evolved from the pre-main sequence (PMS) to the end of hydrogen burning, the white dwarf cooling sequence, or the end of carbon burning, depending on the initial mass. We also provide a grid of models evolved from the PMS to the end of core helium burning for . We showcase extensive comparisons with observational constraints as well as with some of the most widely used existing models in the literature. The evolutionary tracks and isochrones can be downloaded from the project website at http://waps.cfa.harvard.edu/MIST/ .

ABSTRACT We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to reduce the uncertainty in the local value of the Hubble constant from 3.3% to 2.4%. The bulk of this improvement comes from new near-infrared (NIR) observations of Cepheid variables in 11 host galaxies of recent type Ia supernovae (SNe Ia), more than doubling the sample of reliable SNe Ia having a Cepheid-calibrated distance to a total of 19; these in turn leverage the magnitude-redshift relation based on ∼300 SNe Ia at z < 0.15. All 19 hosts as well as the megamaser system NGC 4258 have been observed with WFC3 in the optical and NIR, thus nullifying cross-instrument zeropoint errors in the relative distance estimates from Cepheids. Other noteworthy improvements include a 33% reduction in the systematic uncertainty in the maser distance to NGC 4258, a larger sample of Cepheids in the Large Magellanic Cloud (LMC), a more robust distance to the LMC based on late-type detached eclipsing binaries (DEBs), HST observations of Cepheids in M31, and new HST -based trigonometric parallaxes for Milky Way (MW)…

ABSTRACT Nucleosynthesis, light curves, explosion energies, and remnant masses are calculated for a grid of supernovae (SNe) resulting from massive stars with solar metallicity and masses from 9.0 to 120 M ⊙ . The full evolution is followed using an adaptive reaction network of up to 2000 nuclei. A novel aspect of the survey is the use of a one-dimensional neutrino transport model for the explosion. This explosion model has been calibrated to give the observed energy for SN 1987A, using five standard progenitors, and for the Crab SN using a 9.6 M ⊙ progenitor. As a result of using a calibrated central engine, the final kinetic energy of the SN is variable and sensitive to the structure of each pre-SN star. Many progenitors with extended core structures do not explode, but become black holes (BHs), and the masses of exploding stars do not form a simply connected set. The resulting nucleosynthesis agrees reasonably well with the Sun provided that a reasonable contribution from SNe Ia is also allowed, but with a deficiency of light s -process isotopes. The resulting neutron star…

ABSTRACT Mass and radius are two of the most fundamental properties of an astronomical object. Increasingly, new planet discoveries are being announced with a measurement of one of these quantities, but not both. This has led to a growing need to forecast the missing quantity using the other, especially when predicting the detectability of certain follow-up observations. We present an unbiased forecasting model built upon a probabilistic mass–radius relation conditioned on a sample of 316 well-constrained objects. Our publicly available code, Forecaster , accounts for observational errors, hyper-parameter uncertainties, and the intrinsic dispersions observed in the calibration sample. By conditioning our model on a sample spanning dwarf planets to late-type stars, Forecaster can predict the mass (or radius) from the radius (or mass) for objects covering nine orders of magnitude in mass. Classification is naturally performed by our model, which uses four classes we label as Terran worlds, Neptunian worlds, Jovian worlds, and stars. Our classification identifies dwarf planets as…

ABSTRACT We analyze 24 binary radio pulsars in the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) nine-year data set. We make 14 significant measurements of the Shapiro delay, including new detections in four pulsar-binary systems (PSRs J0613−0200, J2017+0603, J2302+4442, and J2317+1439), and derive estimates of the binary-component masses and orbital inclination for these MSP-binary systems. We find a wide range of binary pulsar masses, with values as low as for PSR J1918−0642 and as high as for PSR J1614−2230 (both 68.3% credibility). We make an improved measurement of the Shapiro timing delay in the PSR J1918−0642 and J2043+1711 systems, measuring the pulsar mass in the latter system to be (68.3% credibility) for the first time. We measure secular variations of one or more orbital elements in many systems, and use these measurements to further constrain our estimates of the pulsar and companion masses whenever possible. In particular, we used the observed Shapiro delay and periastron advance due to relativistic gravity in the PSR J1903+0327 system to…

ABSTRACT We present the first high-resolution sub-millimeter survey of both dust and gas for a large population of protoplanetary disks. Characterizing fundamental properties of protoplanetary disks on a statistical level is critical to understanding how disks evolve into the diverse exoplanet population. We use the Atacama Large Millimeter/Submillimeter Array (ALMA) to survey 89 protoplanetary disks around stars with in the young (1–3 Myr), nearby (150–200 pc) Lupus complex. Our observations cover the 890 μ m continuum and the 13 CO and C 18 O 3–2 lines. We use the sub-millimeter continuum to constrain to a few Martian masses (0.2–0.4 M ⊕ ) and the CO isotopologue lines to constrain to roughly a Jupiter mass (assuming an interstellar medium (ISM)-like abundance). Of 89 sources, we detect 62 in continuum, 36 in 13 CO, and 11 in C 18 O at significance. Stacking individually undetected sources limits their average dust mass to Lunar masses (0.03 M ⊕ ), indicating rapid evolution once disk clearing begins. We find a positive correlation between and M * , and present the first evidence…

ABSTRACT We present Hubble WFC3/IR slitless grism spectra of a remarkably bright z ≳ 10 galaxy candidate, GN-z11, identified initially from CANDELS/GOODS-N imaging data. A significant spectroscopic continuum break is detected at . The new grism data, combined with the photometric data, rule out all plausible lower redshift solutions for this source. The only viable solution is that this continuum break is the Ly α break redshifted to , just ∼400 Myr after the Big Bang. This observation extends the current spectroscopic frontier by 150 Myr to well before the Planck (instantaneous) cosmic reionization peak at z ∼ 8.8, demonstrating that galaxy build-up was well underway early in the reionization epoch at z > 10. GN-z11 is remarkably, and unexpectedly, luminous for a galaxy at such an early time: its UV luminosity is 3× larger than measured at z ∼ 6−8. The Spitzer IRAC detections up to 4.5 μ m of this galaxy are consistent with a stellar mass of ∼10 9 M ⊙ . This spectroscopic redshift measurement suggests that James Webb Space Telescope ( JWST ) will be able to similarly and easily…

ABSTRACT The disk mass is among the most important input parameter for every planet formation model to determine the number and masses of the planets that can form. We present an ALMA 887 μ m survey of the disk population around objects from ∼2 to 0.03 M ⊙ in the nearby ∼2 Myr old Chamaeleon I star-forming region. We detect thermal dust emission from 66 out of 93 disks, spatially resolve 34 of them, and identify two disks with large dust cavities of about 45 au in radius. Assuming isothermal and optically thin emission, we convert the 887 μ m flux densities into dust disk masses, hereafter M dust . We find that the relation is steeper than linear and of the form M dust ∝ ( M * ) 1.3–1.9 , where the range in the power-law index reflects two extremes of the possible relation between the average dust temperature and stellar luminosity. By reanalyzing all millimeter data available for nearby regions in a self-consistent way, we show that the 1–3 Myr old regions of Taurus, Lupus, and Chamaeleon I share the same relation, while the 10 Myr old Upper Sco association has a steeper relation.…

ABSTRACT ALMA Cycle 2 observations of long-wavelength dust emission in 145 star-forming galaxies are used to probe the evolution of the star-forming interstellar medium (ISM). We also develop a physical basis and empirical calibration (with 72 low- z and z ∼ 2 galaxies) for using the dust continuum as a quantitative probe of ISM masses. The galaxies with the highest star formation rates (SFRs) at = 2.2 and 4.4 have gas masses up to 100 times that of the Milky Way and gas mass fractions reaching 50%–80%, i.e., gas masses 1-4× their stellar masses. We find a single high- z star formation law: yr −1 —an approximately linear dependence on the ISM mass and an increased star formation efficiency per unit gas mass at higher redshift. Galaxies above the main sequence (MS) have larger gas masses but are converting their ISM into stars on a timescale only slightly shorter than those on the MS; thus, these “starbursts” are largely the result of having greatly increased gas masses rather than an increased efficiency of converting gas to stars. At z > 1, the entire population of star-forming…

ABSTRACT The COSMOS-Legacy survey is a 4.6 Ms Chandra program that has imaged 2.2 deg2 of the COSMOS field with an effective exposure of ks over the central 1.5 deg2 and of ks in the remaining area. The survey is the combination of 56 new observations obtained as an X-ray Visionary Project with the previous C-COSMOS survey. We describe the reduction and analysis of the new observations and the properties of 2273 point sources detected above a spurious probability of 2 × 10−5. We also present the updated properties of the C-COSMOS sources detected in the new data. The whole survey includes 4016 point sources (3814, 2920 and 2440 in the full, soft, and hard band). The limiting depths are 2.2 × 10−16, 1.5 × 10−15, and 8.9 × 10−16 in the 0.5–2, 2–10, and 0.5–10 keV bands, respectively. The observed fraction of obscured active galactic nuclei with a column density >1022 cm−2 from the hardness ratio (HR) is ∼50 %. Given the large sample we compute source number counts in the hard and soft bands, significantly reducing the uncertainties of 5%–10%. For the first time we compute number…

ABSTRACT The IceCube Collaboration has previously discovered a high-energy astrophysical neutrino flux using neutrino events with interaction vertices contained within the instrumented volume of the IceCube detector. We present a complementary measurement using charged current muon neutrino events where the interaction vertex can be outside this volume. As a consequence of the large muon range the effective area is significantly larger but the field of view is restricted to the Northern Hemisphere. IceCube data from 2009 through 2015 have been analyzed using a likelihood approach based on the reconstructed muon energy and zenith angle. At the highest neutrino energies between and a significant astrophysical contribution is observed, excluding a purely atmospheric origin of these events at significance. The data are well described by an isotropic, unbroken power-law flux with a normalization at neutrino energy of and a hard spectral index of . The observed spectrum is harder in comparison to previous IceCube analyses with lower energy thresholds which may indicate a break in the…

ABSTRACT Since 2012 August Voyager 1 has been observing the local interstellar energy spectra of Galactic cosmic-ray nuclei down to 3 MeV nuc −1 and electrons down to 2.7 MeV. The H and He spectra have the same energy dependence between 3 and 346 MeV nuc −1 , with a broad maximum in the 10–50 MeV nuc −1 range and a H/He ratio of 12.2 ± 0.9. The peak H intensity is ∼15 times that observed at 1 AU, and the observed local interstellar gradient of 3–346 MeV H is −0.009 ± 0.055% AU −1 , consistent with models having no local interstellar gradient. The energy spectrum of electrons ( e − + e + ) with 2.7–74 MeV is consistent with E −1.30±0.05 and exceeds the H intensity at energies below ∼50 MeV. Propagation model fits to the observed spectra indicate that the energy density of cosmic-ray nuclei with >3 MeV nuc −1 and electrons with >3 MeV is 0.83–1.02 eV cm −3 and the ionization rate of atomic H is in the range of 1.51–1.64 × 10 −17 s −1 . This rate is a factor >10 lower than the ionization rate in diffuse interstellar clouds, suggesting significant spatial inhomogeneity in low-energy…

ABSTRACT We present astrophysical false positive probability calculations for every Kepler Object of Interest (KOI)—the first large-scale demonstration of a fully automated transiting planet validation procedure. Out of 7056 KOIs, we determine that 1935 have probabilities <1% of being astrophysical false positives, and thus may be considered validated planets. Of these, 1284 have not yet been validated or confirmed by other methods. In addition, we identify 428 KOIs that are likely to be false positives, but have not yet been identified as such, though some of these may be a result of unidentified transit timing variations. A side product of these calculations is full stellar property posterior samplings for every host star, modeled as single, binary, and triple systems. These calculations use vespa , a publicly available Python package that is able to be easily applied to any transiting exoplanet candidate.

ABSTRACT Exoplanet discoveries of recent years have provided a great deal of new data for studying the bulk compositions of giant planets. Here we identify 47 transiting giant planets (20 M ⊕ < M < 20 M J ) whose stellar insolations are low enough ( F * < 2 × 10 8 erg s −1 cm −2 , or roughly T eff < 1000) that they are not affected by the hot-Jupiter radius inflation mechanism(s). We compute a set of new thermal and structural evolution models and use these models in comparison with properties of the 47 transiting planets (mass, radius, age) to determine their heavy element masses. A clear correlation emerges between the planetary heavy element mass M z and the total planet mass, approximately of the form . This finding is consistent with the core-accretion model of planet formation. We also study how stellar metallicity [Fe/H] affects planetary metal-enrichment and find a weaker correlation than has previously been reported from studies with smaller sample sizes. We confirm a strong relationship between the planetary metal-enrichment relative to the parent star Z planet / Z star…

ABSTRACT Ground- and space-based planet searches employing radial velocity techniques and transit photometry have detected thousands of planet-hosting stars in the Milky Way. With so many planets discovered, the next step toward identifying potentially habitable planets is atmospheric characterization. While the Sun–Earth system provides a good framework for understanding the atmospheric chemistry of Earth-like planets around solar-type stars, the observational and theoretical constraints on the atmospheres of rocky planets in the habitable zones (HZs) around low-mass stars (K and M dwarfs) are relatively few. The chemistry of these atmospheres is controlled by the shape and absolute flux of the stellar spectral energy distribution (SED), however, flux distributions of relatively inactive low-mass stars are poorly understood at present. To address this issue, we have executed a panchromatic (X-ray to mid-IR) study of the SEDs of 11 nearby planet-hosting stars, the Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanetary Systems (MUSCLES) Treasury Survey. The…

ABSTRACT Several small dense exoplanets are now known, inviting comparisons to Earth and Venus. Such comparisons require translating their masses and sizes to composition models of evolved multi-layer interior planets. Such theoretical models rely on our understanding of the Earth’s interior, as well as independently derived equations of state, but so far have not involved direct extrapolations from Earth’s seismic model: the Preliminary Reference Earth Model (PREM). To facilitate more detailed compositional comparisons between small exoplanets and the Earth, we derive here a semi-empirical mass–radius relation for two-layer rocky planets based on PREM, , where CMF stands for core mass fraction. It is applicable to 1 ∼ 8 M ⊕ and a CMF of 0.0 ∼ 0.4. Applying this formula to Earth and Venus and several known small exoplanets with radii and masses measured to better than ∼30% precision gives a CMF fit of 0.26 ± 0.07.

ABSTRACT We present a combined analysis of rest-frame far-UV (FUV; 1000–2000 Å) and rest-frame optical (3600–7000 Å) composite spectra formed from very deep Keck/LRIS and Keck/MOSFIRE observations of a sample of 30 star-forming galaxies with , selected to be broadly representative of the full KBSS-MOSFIRE spectroscopic survey. Since the same massive stars are responsible for the observed FUV continuum and for the excitation of the observed nebular emission, a self-consistent stellar population synthesis model should simultaneously match the details of the FUV stellar+nebular continuum and—when inserted as the excitation source in photoionization models—predict all observed nebular emission line ratios. We find that only models including massive star binaries, having low stellar metallicity ( ) but relatively high nebular (ionized gas-phase) abundances ( ), can successfully match all of the observational constraints. We show that this apparent discrepancy is naturally explained by highly super-solar O/Fe ( ), expected for a gas whose enrichment is dominated by the products of…

ABSTRACT Motivated by the recent detection of gravitational waves from the black hole binary merger GW150914, we study the dynamical evolution of (stellar-mass) black holes in galactic nuclei, where massive star clusters reside. With masses of and sizes of only a few parsecs, nuclear star clusters (NSCs) are the densest stellar systems observed in the local universe and represent a robust environment where black hole binaries can dynamically form, harden, and merge. We show that due to their large escape speeds, NSCs can retain a large fraction of their merger remnants. Successive mergers can then lead to significant growth and produce black hole mergers of several tens of solar masses similar to GW150914 and up to a few hundreds of solar masses, without the need to invoke extremely low metallicity environments. We use a semi-analytical approach to describe the dynamics of black holes in massive star clusters. Our models give a black hole binary merger rate of from NSCs, implying up to a few tens of possible detections per year with Advanced LIGO. Moreover, we find a local merger…

ABSTRACT Thus far, judging the fate of a massive star (either a neutron star [NS] or a black hole) solely by its structure prior to core collapse has been ambiguous. Our work and previous attempts find a nonmonotonic variation of successful and failed supernovae with zero-age main-sequence mass, for which no single structural parameter can serve as a good predictive measure. However, we identify two parameters computed from the pre-collapse structure of the progenitor, which in combination allow for a clear separation of exploding and nonexploding cases with only a few exceptions (∼1%–2.5%) in our set of 621 investigated stellar models. One parameter is M 4 , defining the normalized enclosed mass for a dimensionless entropy per nucleon of s = 4, and the other is , being the normalized mass derivative at this location. The two parameters μ 4 and M 4 μ 4 can be directly linked to the mass-infall rate, , of the collapsing star and the electron-type neutrino luminosity of the accreting proto-NS, , which play a crucial role in the “critical luminosity” concept for the theoretical…

ABSTRACT We present a comprehensive study of spectroscopic radius measurements of twelve neutron stars obtained during thermonuclear bursts or in quiescence. We incorporate, for the first time, a large number of systematic uncertainties in the measurement of the apparent angular sizes, Eddington fluxes, and distances, in the composition of the interstellar medium, and in the flux calibration of X-ray detectors. We also take into account the results of recent theoretical calculations of rotational effects on neutron star radii, of atmospheric effects on surface spectra, and of relativistic corrections to the Eddington critical flux. We employ Bayesian statistical frameworks to obtain neutron star radii from the spectroscopic measurements as well as to infer the equation of state from the radius measurements. Combining these with the results of experiments in the vicinity of nuclear saturation density and the observations of neutron stars, we place strong and quantitative constraints on the properties of the equation of state between times the nuclear saturation density. We find that…

ABSTRACT This study presents a catalog of 8107 molecular clouds that covers the entire Galactic plane and includes 98% of the 12 CO emission observed within . The catalog was produced using a hierarchical cluster identification method applied to the result of a Gaussian decomposition of the Dame et al. data. The total H 2 mass in the catalog is , in agreement with previous estimates. We find that 30% of the sight lines intersect only a single cloud, with another 25% intersecting only two clouds. The most probable cloud size is pc. We find that , with no correlation between the cloud surface density, Σ, and R . In contrast with the general idea, we find a rather large range of values of Σ, from 2 to 300 M ⊙ pc −2 , and a systematic decrease with increasing Galactic radius, . The cloud velocity dispersion and the normalization both decrease systematically with . When studied over the whole Galactic disk, there is a large dispersion in the line width–size relation and a significantly better correlation between and . The normalization of this correlation is constant to better than a…

ABSTRACT The Fermi Large Area Telescope (LAT) has provided the most detailed view to date of the emission toward the Galactic center (GC) in high-energy γ -rays. This paper describes the analysis of data taken during the first 62 months of the mission in the energy range 1–100 GeV from a 15° × 15° region about the direction of the GC. Specialized interstellar emission models (IEMs) are constructed to enable the separation of the γ -ray emissions produced by cosmic ray particles interacting with the interstellar gas and radiation fields in the Milky Way into that from the inner ∼1 kpc surrounding the GC, and that from the rest of the Galaxy. A catalog of point sources for the 15° × 15° region is self-consistently constructed using these IEMs: the First Fermi -LAT Inner Galaxy Point Source Catalog (1FIG). The spatial locations, fluxes, and spectral properties of the 1FIG sources are presented, and compared with γ -ray point sources over the same region taken from existing catalogs. After subtracting the interstellar emission and point-source contributions a residual is found. If…

ABSTRACT We explore how well spectra from the James Webb Space Telescope (JWST) will likely constrain bulk atmospheric properties of transiting exoplanets. We start by modeling the atmospheres of archetypal hot Jupiter, warm Neptune, warm sub-Neptune, and cool super-Earth planets with atmospheres that are clear, cloudy, or of high mean molecular weight (HMMW). Next we simulate the λ = 1–11 μm transmission and emission spectra of these systems for several JWST instrument modes for single-transit or single-eclipse events. We then perform retrievals to determine how well temperatures and molecular mixing ratios (CH4, CO, CO2, H2O, NH3) can be constrained. We find that λ = 1–2.5 μm transmission spectra will often constrain the major molecular constituents of clear solar-composition atmospheres well. Cloudy or HMMW atmospheres will often require full 1–11 μm spectra for good constraints, and emission data may be more useful in cases of sufficiently high F p and high F p /F *. Strong temperature inversions in the solar-composition hot-Jupiter atmosphere should be detectable with 1–2.5+ μm…

ABSTRACT The composition of a planet’s atmosphere is determined by its formation, evolution, and present-day insolation. A planet’s spectrum therefore may hold clues on its origins. We present a “chain” of models, linking the formation of a planet to its observable present-day spectrum. The chain links include (1) the planet’s formation and migration, (2) its long-term thermodynamic evolution, (3) a variety of disk chemistry models, (4) a non-gray atmospheric model, and (5) a radiometric model to obtain simulated spectroscopic observations with James Webb Space Telescope and ARIEL. In our standard chemistry model the inner disk is depleted in refractory carbon as in the Solar System and in white dwarfs polluted by extrasolar planetesimals. Our main findings are: (1) envelope enrichment by planetesimal impacts during formation dominates the final planetary atmospheric composition of hot Jupiters. We investigate two, under this finding, prototypical formation pathways: a formation inside or outside the water iceline, called “dry” and “wet” planets, respectively. (2) Both the “dry” and…

ABSTRACT A homogeneous search for stellar flares has been performed using every available Kepler light curve. An iterative light curve de-trending approach was used to filter out both astrophysical and systematic variability to detect flares. The flare recovery completeness has also been computed throughout each light curve using artificial flare injection tests, and the tools for this work have been made publicly available. The final sample contains 851,168 candidate flare events recovered above the 68% completeness threshold, which were detected from 4041 stars, or 1.9% of the stars in the Kepler database. The average flare energy detected is ∼10 35 erg. The net fraction of flare stars increases with g − i color, or decreasing stellar mass. For stars in this sample with previously measured rotation periods, the total relative flare luminosity is compared to the Rossby number. A tentative detection of flare activity saturation for low-mass stars with rapid rotation below a Rossby number of ∼0.03 is found. A power-law decay in flare activity with Rossby number is found with a slope…

ABSTRACT To date, the Burst Alert Telescope (BAT) onboard Swift has detected ∼1000 gamma-ray bursts (GRBs), of which ∼360 GRBs have redshift measurements, ranging from z = 0.03 to z = 9.38. We present the analyses of the BAT-detected GRBs for the past ∼11 years up through GRB 151027B. We report summaries of both the temporal and spectral analyses of the GRB characteristics using event data (i.e., data for each photon within approximately 250 s before and 950 s after the BAT trigger time), and discuss the instrumental sensitivity and selection effects of GRB detections. We also explore the GRB properties with redshift when possible. The result summaries and data products are available at http://swift.gsfc.nasa.gov/results/batgrbcat/index.html. In addition, we perform searches for GRB emissions before or after the event data using the BAT survey data. We estimate the false detection rate to be only one false detection in this sample. There are 15 ultra-long GRBs (∼2% of the BAT GRBs) in this search with confirmed emission beyond ∼1000 s of event data, and only two GRBs (GRB 100316D…

ABSTRACT The latest observation of HL Tau by ALMA revealed spectacular concentric dust rings in its circumstellar disk. We attempt to explain the multiple ring structure as a consequence of aggregate sintering. Sintering is known to reduce the sticking efficiency of dust aggregates and occurs at temperatures slightly below the sublimation point of the constituent material. We present a dust growth model that incorporates sintering and use it to simulate global dust evolution due to sintering, coagulation, fragmentation, and radial inward drift in a modeled HL Tau disk. We show that aggregates consisting of multiple species of volatile ices experience sintering, collisionally disrupt, and pile up at multiple locations slightly outside the snow lines of the volatiles. At wavelengths of 0.87–1.3 mm, these sintering zones appear as bright, optically thick rings with a spectral slope of ≈ 2 , whereas the non-sintering zones appear as darker, optically thinner rings of a spectral slope of ≈ 2.3 –2.5. The observational features of the sintering and non-sintering zones are consistent with…

ABSTRACT One promising electromagnetic signature of compact object mergers are kilonovae: approximately isotropic radioactively powered transients that peak days to weeks post-merger. Key uncertainties in kilonova modeling include the emission profiles of the radioactive decay products—non-thermal -particles, -particles, fission fragments, and -rays—and the efficiency with which their kinetic energy is absorbed by the ejecta. The radioactive energy emitted, along with its thermalization efficiency, sets the luminosity budget and is therefore crucial for predicting kilonova light curves. We outline uncertainties in the radioactivity, describe the processes by which the decay products transfer energy to the ejecta, and calculate time-dependent thermalization efficiencies for each particle type. We determine the net thermalization efficiency and explore its dependence on r -process yields—in particular, the production of -decaying translead nuclei—and on ejecta mass, velocity, and magnetic fields. We incorporate our results into detailed radiation transport simulations, and calculate…

ABSTRACT We study the formation of planetesimals in protoplanetary disks from the gravitational collapse of solid over-densities generated via the streaming instability. To carry out these studies, we implement and test a particle-mesh self-gravity module for the Athena code that enables the simulation of aerodynamically coupled systems of gas and collisionless self-gravitating solid particles. Upon employment of our algorithm to planetesimal formation simulations, we find that (when a direct comparison is possible) the Athena simulations yield predicted planetesimal properties that agree well with those found in prior work using different numerical techniques. In particular, the gravitational collapse of streaming-initiated clumps leads to an initial planetesimal mass function that is well-represented by a power law, , with , which equates to a differential size distribution of , with . We find no significant trends with resolution from a convergence study of up to 5123 grid zones and particles. Likewise, the power-law slope appears indifferent to changes in the relative strength…

ABSTRACT We present the catalog of optical and infrared counterparts of the Chandra COSMOS-Legacy Survey, a 4.6 Ms Chandra program on the 2.2 deg2 of the COSMOS field, combination of 56 new overlapping observations obtained in Cycle 14 with the previous C-COSMOS survey. In this Paper we report the i, K, and 3.6 μm identifications of the 2273 X-ray point sources detected in the new Cycle 14 observations. We use the likelihood ratio technique to derive the association of optical/infrared (IR) counterparts for 97% of the X-ray sources. We also update the information for the 1743 sources detected in C-COSMOS, using new K and 3.6 μm information not available when the C-COSMOS analysis was performed. The final catalog contains 4016 X-ray sources, 97% of which have an optical/IR counterpart and a photometric redshift, while ≃54% of the sources have a spectroscopic redshift. The full catalog, including spectroscopic and photometric redshifts and optical and X-ray properties described here in detail, is available online. We study several X-ray to optical (X/O) properties: with our large…

ABSTRACT We present the discovery of nine quasars at identified in the Sloan Digital Sky Survey (SDSS) imaging data. This completes our survey of quasars in the SDSS footprint. Our final sample consists of 52 quasars at , including 29 quasars with mag selected from 11,240 deg2 of the SDSS single-epoch imaging survey (the main survey), 10 quasars with selected from 4223 deg2 of the SDSS overlap regions (regions with two or more imaging scans), and 13 quasars down to mag from the 277 deg2 in Stripe 82. They span a wide luminosity range of . This well-defined sample is used to derive the quasar luminosity function (QLF) at . After combining our SDSS sample with two faint ( mag) quasars from the literature, we obtain the parameters for a double power-law fit to the QLF. The bright-end slope β of the QLF is well constrained to be . Due to the small number of low-luminosity quasars, the faint-end slope α and the characteristic magnitude are less well constrained, with and mag. The spatial density of luminous quasars, parametrized as , drops rapidly from to 6, with . Based on our fitted…

ABSTRACT We study the abundance of substructure in the matter density near galaxies using ALMA Science Verification observations of the strong lensing system SDP.81. We present a method to measure the abundance of subhalos around galaxies using interferometric observations of gravitational lenses. Using simulated ALMA observations we explore the effects of various systematics, including antenna phase errors and source priors, and show how such errors may be measured or marginalized. We apply our formalism to ALMA observations of SDP.81. We find evidence for the presence of a M = 108.96±0.12 M ⊙ subhalo near one of the images, with a significance of 6.9σ in a joint fit to data from bands 6 and 7; the effect of the subhalo is also detected in both bands individually. We also derive constraints on the abundance of dark matter (DM) subhalos down to M ∼ 2 × 107 M ⊙, pushing down to the mass regime of the smallest detected satellites in the Local Group, where there are significant discrepancies between the observed population of luminous galaxies and predicted DM subhalos. We find hints…

ABSTRACT 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., / ), 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…

ABSTRACT 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 ( ) and logarithmic stellar mass ( ) that holds for galaxies with . We use simulations to validate our method of measuring the slope of the –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,…

ABSTRACT Over a large range of equilibrium temperatures, clouds shape the transmission spectrum of hot Jupiter atmospheres, yet their composition remains unknown. Recent observations show that the Kepler light curves of some hot Jupiters are asymmetric: for the hottest planets, the light curve peaks before secondary eclipse, whereas for planets cooler than ∼1900 K, it peaks after secondary eclipse. We use the thermal structure from 3D global circulation models to determine the expected cloud distribution and Kepler light curves of hot Jupiters. We demonstrate that the change from an optical light curve dominated by thermal emission to one dominated by scattering (reflection) naturally explains the observed trend from negative to positive offset. For the cool planets the presence of an asymmetry in the Kepler light curve is a telltale sign of the cloud composition, because each cloud species can produce an offset only over a narrow range of effective temperatures. By comparing our models and the observations, we show that the cloud composition of hot Jupiters likely varies with…

ABSTRACT We explore star formation histories (SFHs) of galaxies based on the evolution of the star formation rate stellar mass relation (SFR–M *). Using data from the FourStar Galaxy Evolution Survey (ZFOURGE) in combination with far-IR imaging from the Spitzer and Herschel observatories we measure the SFR–M * relation at 0.5 < z < 4. Similar to recent works we find that the average infrared spectral energy distributions of galaxies are roughly consistent with a single infrared template across a broad range of redshifts and stellar masses, with evidence for only weak deviations. We find that the SFR–M * relation is not consistent with a single power law of the form at any redshift; it has a power law slope of α ∼ 1 at low masses, and becomes shallower above a turnover mass (M 0) that ranges from 109.5 to 1010.8 M ⊙, with evidence that M 0 increases with redshift. We compare our measurements to results from state-of-the-art cosmological simulations, and find general agreement in the slope of the SFR–M * relation albeit with systematic offsets. We use the evolving SFR–M * sequence to…

ABSTRACT We compute upper limits on the nanohertz-frequency isotropic stochastic gravitational wave background (GWB) using the 9 year data set from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) collaboration. Well-tested Bayesian techniques are used to set upper limits on the dimensionless strain amplitude (at a frequency of 1 yr−1) for a GWB from supermassive black hole binaries of A gw < 1.5 × 10 − 15 . We also parameterize the GWB spectrum with a broken power-law model by placing priors on the strain amplitude derived from simulations of Sesana and McWilliams et al. Using Bayesian model selection we find that the data favor a broken power law to a pure power law with odds ratios of 2.2 and 22 to one for the Sesana and McWilliams prior models, respectively. Using the broken power-law analysis we construct posterior distributions on environmental factors that drive the binary to the GW-driven regime including the stellar mass density for stellar-scattering, mass accretion rate for circumbinary disk interaction, and orbital eccentricity for eccentric…

ABSTRACT We investigate the evolution of NOAA Active Region (AR) 11817 during 2013 August 10–12, when it developed a complex field configuration and produced four confined, followed by two eruptive, flares. These C-and-above flares are all associated with a magnetic flux rope (MFR) located along the major polarity inversion line, where shearing and converging photospheric flows are present. Aided by the nonlinear force-free field modeling, we identify the MFR through mapping magnetic connectivities and computing the twist number for each individual field line. The MFR is moderately twisted ( ) and has a well-defined boundary of high squashing factor Q . We found that the field line with the extremum is a reliable proxy of the rope axis, and that the MFR's peak temporarily increases within half an hour before each flare while it decreases after the flare peak for both confined and eruptive flares. This pre-flare increase in has little effect on the AR's free magnetic energy or any other parameters derived for the whole region, due to its moderate amount and the MFR's relatively small…

ABSTRACT The riddle posed by super-Earths (1–4R ⊕, 2–20M ⊕) is that they are not Jupiters: their core masses are large enough to trigger runaway gas accretion, yet somehow super-Earths accreted atmospheres that weigh only a few percent of their total mass. We show that this puzzle is solved if super-Earths formed late, as the last vestiges of their parent gas disks were about to clear. This scenario would seem to present fine-tuning problems, but we show that there are none. Ambient gas densities can span many (in one case up to 9) orders of magnitude, and super-Earths can still robustly emerge after ∼0.1–1 Myr with percent-by-weight atmospheres. Super-Earth cores are naturally bred in gas-poor environments where gas dynamical friction has weakened sufficiently to allow constituent protocores to gravitationally stir one another and merge. So little gas is present at the time of core assembly that cores hardly migrate by disk torques: formation of super-Earths can be in situ. The basic picture—that close-in super-Earths form in a gas-poor (but not gas-empty) inner disk, fed…

ABSTRACT We report on radio and X-ray observations of the only known repeating Fast Radio Burst (FRB) source, FRB 121102. We have detected six additional radio bursts from this source: five with the Green Bank Telescope at 2 GHz, and one at 1.4 GHz with the Arecibo Observatory, for a total of 17 bursts from this source. All have dispersion measures consistent with a single value (∼559 pc cm −3 ) that is three times the predicted maximum Galactic contribution. The 2 GHz bursts have highly variable spectra like those at 1.4 GHz, indicating that the frequency structure seen across the individual 1.4 and 2 GHz bandpasses is part of a wideband process. X-ray observations of the FRB 121102 field with the Swift and Chandra observatories show at least one possible counterpart; however, the probability of chance superposition is high. A radio imaging observation of the field with the Jansky Very Large Array at 1.6 GHz yields a 5 σ upper limit of 0.3 mJy on any point-source continuum emission. This upper limit, combined with archival Wide-field Infrared Survey Explorer 22 μ m and IPHAS H α…

ABSTRACT We present ground-based optical photometric monitoring data for NGC 5548, part of an extended multiwavelength reverberation mapping campaign. The light curves have nearly daily cadence from 2014 January to July in nine filters (BVRI and ugriz). Combined with ultraviolet data from the Hubble Space Telescope and Swift, we confirm significant time delays between the continuum bands as a function of wavelength, extending the wavelength coverage from 1158 Å to the z band (~9160 Å). We find that the lags at wavelengths longer than the V band are equal to or greater than the lags of high-ionization-state emission lines (such as He ii λ 1640 and λ 4686 ), suggesting that the continuum-emitting source is of a physical size comparable to the inner broad-line region (BLR). The trend of lag with wavelength is broadly consistent with the prediction for continuum reprocessing by an accretion disk with τ ∝ λ 4 / 3 . However, the lags also imply a disk radius that is 3 times larger than the prediction from standard thin-disk theory, assuming that the bolometric luminosity is 10% of the…

ABSTRACT Hot Jupiters, giant extrasolar planets with orbital periods shorter than ∼10 days, have long been thought to form at large radial distances, only to subsequently experience long-range inward migration. Here, we offer the contrasting view that a substantial fraction of the hot Jupiter population formed in situ via the core-accretion process. We show that under conditions appropriate to the inner regions of protoplanetary disks, rapid gas accretion can be initiated by super-Earth-type planets, comprising 10–20 Earth masses of refractory material. An in situ formation scenario leads to testable consequences, including the expectation that hot Jupiters should frequently be accompanied by additional low-mass planets with periods shorter than ∼100 days. Our calculations further demonstrate that dynamical interactions during the early stages of planetary systems’ lifetimes should increase the inclinations of such companions, rendering transits rare. High-precision radial velocity monitoring provides the best prospect for their detection.

ABSTRACT We present high-resolution (0.″16) 870 μ m Atacama Large Millimeter/submillimeter Array (ALMA) imaging of 16 luminous ( ) submillimeter galaxies (SMGs) from the ALESS survey of the Extended Chandra Deep Field South. This dust imaging traces the dust-obscured star formation in these galaxies on ∼1.3 kpc scales. The emission has a median effective radius of R e = 0.″24 ± 0.″02, corresponding to a typical physical size of 1.8 ± 0.2 kpc. We derive a median Sérsic index of n = 0.9 ± 0.2, implying that the dust emission is remarkably disk-like at the current resolution and sensitivity. We use different weighting schemes with the visibilities to search for clumps on 0.″12 (∼1.0 kpc) scales, but we find no significant evidence for clumping in the majority of cases. Indeed, we demonstrate using simulations that the observed morphologies are generally consistent with smooth exponential disks, suggesting that caution should be exercised when identifying candidate clumps in even moderate signal-to-noise ratio interferometric data. We compare our maps to comparable-resolution Hubble…

ABSTRACT Direct Lyα imaging of intergalactic gas at has recently revealed giant cosmological structures around quasars, e.g., the Slug Nebula. Despite their high luminosity, the detection rate of such systems in narrow-band and spectroscopic surveys is less than 10%, possibly encoding crucial information on the distribution of gas around quasars and the quasar emission properties. In this study, we use the MUSE integral-field instrument to perform a blind survey for giant nebulae around 17 bright radio-quiet quasars at that does not suffer from most of the limitations of previous surveys. After data reduction and analysis performed with specifically developed tools, we found that each quasar is surrounded by giant nebulae with projected sizes larger than 100 physical kiloparsecs and, in some cases, extending up to 320 kpc. The circularly averaged surface brightness profiles of the nebulae appear to be very similar to each other despite their different morphologies and are consistent with power laws with slopes . The similarity between the properties of all these nebulae and the Slug…

ABSTRACT We present ALMA observations of 106 G-, K-, and M-type stars in the Upper Scorpius OB Association hosting circumstellar disks. With these data, we measure the 0.88 mm continuum and 12CO J = 3–2 line fluxes of disks around low-mass (0.14–1.66 M ⊙) stars at an age of 5–11 Myr. Of the 75 primordial disks in the sample, 53 are detected in the dust continuum and 26 in CO. Of the 31 disks classified as debris/evolved transitional disks, five are detected in the continuum and none in CO. The lack of CO emission in approximately half of the disks with detected continuum emission can be explained if CO is optically thick but has a compact emitting area (≲40 au), or if the CO is heavily depleted by a factor of at least ∼1000 relative to interstellar medium abundances and is optically thin. The continuum measurements are used to estimate the dust mass of the disks. We find a correlation between disk dust mass and stellar host mass consistent with a power-law relation of . Disk dust masses in Upper Sco are compared to those measured in the younger Taurus star-forming region to…

ABSTRACT The spiral arms of the Milky Way are being accurately located for the first time via trigonometric parallaxes of massive star-forming regions with the Bar and Spiral Structure Legacy Survey, using the Very Long Baseline Array and the European VLBI Network, and with the Japanese VLBI Exploration of Radio Astrometry project. Here we describe a computer program that leverages these results to significantly improve the accuracy and reliability of distance estimates to other sources that are known to follow spiral structure. Using a Bayesian approach, sources are assigned to arms based on their (l, b, v) coordinates with respect to arm signatures seen in CO and H i surveys. A source's kinematic distance, displacement from the plane, and proximity to individual parallax sources are also considered in generating a full distance probability density function. Using this program to estimate distances to large numbers of star-forming regions, we generate a realistic visualization of the Milky Way's spiral structure as seen from the northern hemisphere.

ABSTRACT We present new, more precise measurements of the mass and distance of our Galaxy’s central supermassive black hole, Sgr A*. These results stem from a new analysis that more than doubles the time baseline for astrometry of faint stars orbiting Sgr A*, combining 2 decades of speckle imaging and adaptive optics data. Specifically, we improve our analysis of the speckle images by using information about a star’s orbit from the deep adaptive optics data (2005–2013) to inform the search for the star in the speckle years (1995–2005). When this new analysis technique is combined with the first complete re-reduction of Keck Galactic Center speckle images using speckle holography, we are able to track the short-period star S0-38 (K-band magnitude = 17, orbital period = 19 yr) through the speckle years. We use the kinematic measurements from speckle holography and adaptive optics to estimate the orbits of S0-38 and S0-2 and thereby improve our constraints of the mass (M bh) and distance (R o ) of Sgr A*: M bh = (4.02 ± 0.16 ± 0.04) × 106 M ⊙ and 7.86 ± 0.14 ± 0.04 kpc. The…

ABSTRACT 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…

ABSTRACT We present a multiplicity study of all known protostars (94) in the Perseus molecular cloud from a Karl G. Jansky Very Large Array survey at Ka-band (8 mm and 1 cm) and C-band (4 and 6.6 cm). The observed sample has a bolometric luminosity range between 0.1 L ⊙ and ∼33 L ⊙, with a median of 0.7 L ⊙. This multiplicity study is based on the Ka-band data, having a best resolution of ∼0.″065 (15 au) and separations out to ∼43″ (10,000 au) can be probed. The overall multiplicity fraction (MF) is found to be 0.40 ± 0.06 and the companion star fraction (CSF) is 0.71 ± 0.06. The MF and CSF of the Class 0 protostars are 0.57 ± 0.09 and 1.2 ± 0.2, and the MF and CSF of Class I protostars are both 0.23 ± 0.08. The distribution of companion separations appears bi-modal, with a peak at ∼75 au and another peak at ∼3000 au. Turbulent fragmentation is likely the dominant mechanism on >1000 au scales and disk fragmentation is likely to be the dominant mechanism on <200 au scales. Toward three Class 0 sources we find companions separated by <30 au. These systems have the smallest separations…

ABSTRACT The Kepler Mission has discovered thousands of planets with radii <4 , 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…

ABSTRACT We investigate the correlations between the black hole (BH) mass M BH , the velocity dispersion σ , the bulge mass M Bu , the bulge average spherical density , and its spherical half-mass radius r h , constructing a database of 97 galaxies (31 core ellipticals, 17 power-law ellipticals, 30 classical bulges, and 19 pseudobulges) by joining 72 galaxies from the literature to 25 galaxies observed during our recent SINFONI BH survey. For the first time we discuss the full error covariance matrix. We analyze the well-known M BH – σ and M BH – M Bu relations and establish the existence of statistically significant correlations between M Bu and r h and anticorrelations between M Bu and . We establish five significant bivariate correlations ( M BH – σ – ρ h , M BH – σ – r h , M BH – M Bu – σ , M BH – M Bu – ρ h , M BH – M Bu – r h ) that predict M BH of 77 core and power-law ellipticals and classical bulges with measured and intrinsic scatter as small as dex and dex, respectively, or 0.26 dex when the subsample of 45 galaxies defined by Kormendy & Ho is considered. In contrast,…

ABSTRACT We make use of deep 1.2 mm continuum observations (12.7 μ Jy beam −1 rms) of a 1 arcmin 2 region in the Hubble Ultra Deep Field to probe dust-enshrouded star formation from 330 Lyman-break galaxies spanning the redshift range z = 2–10 (to ∼2–3 M ⊙ yr −1 at 1 σ over the entire range). Given the depth and area of ASPECS, we would expect to tentatively detect 35 galaxies, extrapolating the Meurer z ∼ 0 IRX– β relation to z ≥ 2 (assuming dust temperature T d ∼ 35 K). However, only six tentative detections are found at z ≳ 2 in ASPECS, with just three at >3 σ . Subdividing our z = 2–10 galaxy samples according to stellar mass, UV luminosity, and UV-continuum slope and stacking the results, we find a significant detection only in the most massive (>10 9.75 M ⊙ ) subsample, with an infrared excess (IRX = L IR / L UV ) consistent with previous z ∼ 2 results. However, the infrared excess we measure from our large selection of sub- L ∗ (<10 9.75 M ⊙ ) galaxies is ± 0.34 (bootstrap and formal uncertainties) and ± 0.18 at z = 2–3 and z = 4–10, respectively, lying below even an IRX– β…

ABSTRACT Rotation is a directly observable stellar property, and it drives magnetic field generation and activity through a magnetic dynamo. Main-sequence stars with masses below approximately 0.35 M ⊙ (mid-to-late M dwarfs) are fully convective, and are expected to have a different type of dynamo mechanism than solar-type stars. Measurements of their rotation rates provide insight into these mechanisms, but few rotation periods are available for these stars at field ages. Using photometry from the MEarth Project, we measure rotation periods for 387 nearby, mid-to-late M dwarfs in the northern hemisphere, finding periods from 0.1 to 140 days. The typical rotator has stable, sinusoidal photometric modulations at a semi-amplitude of 0.5%–1%. We find no period–amplitude relation for stars below 0.25 M ⊙ and an anticorrelation between period and amplitude for higher-mass M dwarfs. We highlight the existence of older, slowly rotating stars without H α emission that nevertheless have strong photometric variability. We use parallaxes, proper motions, radial velocities, photometry, and…

ABSTRACT We examine the effects of stellar feedback and bursty star formation on low-mass galaxies ( M star = 2 × 10 6 − 5 × 10 10 M ⊙ ) using the Feedback in Realistic Environments (FIRE) simulations. While previous studies emphasized the impact of feedback on dark matter profiles, we investigate the impact on the stellar component: kinematics, radial migration, size evolution, and population gradients. Feedback-driven outflows/inflows drive significant radial stellar migration over both short and long timescales via two processes: (1) outflowing/infalling gas can remain star-forming, producing young stars that migrate ∼1 kpc within their first 100 Myr, and (2) gas outflows/inflows drive strong fluctuations in the global potential, transferring energy to all stars. These processes produce several dramatic effects. First, galaxies’ effective radii can fluctuate by factors of >2 over ∼200 Myr, and these rapid size fluctuations can account for much of the observed scatter in the radius at fixed M star . Second, the cumulative effects of many outflow/infall episodes steadily heat…

ABSTRACT We report the results of the statistical analysis of planetary signals discovered in MOA-II microlensing survey alert system events from 2007 to 2012. We determine the survey sensitivity as a function of planet–star mass ratio, q, and projected planet–star separation, s, in Einstein radius units. We find that the mass-ratio function is not a single power law, but has a change in slope at q ∼ 10−4, corresponding to ∼20 M ⊕ for the median host-star mass of ∼0.6 . We find significant planetary signals in 23 of the 1474 alert events that are well-characterized by the MOA-II survey data alone. Data from other groups are used only to characterize planetary signals that have been identified in the MOA data alone. The distribution of mass ratios and separations of the planets found in our sample are well fit by a broken power-law model of the form for q > q br and for q < q br, where q br is the mass ratio of the break. We also combine this analysis with the previous analyses of Gould et al. and Cassan et al., bringing the total sample to 30 planets. This combined analysis yields ,…

ABSTRACT The ultraviolet (UV) spectral energy distributions (SEDs) of low-mass (K- and M-type) stars play a critical role in the heating and chemistry of exoplanet atmospheres, but are not observationally well-constrained. Direct observations of the intrinsic flux of the Ly α line (the dominant source of UV photons from low-mass stars) are challenging, as interstellar H i absorbs the entire line core for even the closest stars. To address the existing gap in empirical constraints on the UV flux of K and M dwarfs, the MUSCLES Hubble Space Telescope Treasury Survey has obtained UV observations of 11 nearby M and K dwarfs hosting exoplanets. This paper presents the Ly α and extreme-UV spectral reconstructions for the MUSCLES targets. Most targets are optically inactive, but all exhibit significant UV activity. We use a Markov Chain Monte Carlo technique to correct the observed Ly α profiles for interstellar absorption, and we employ empirical relations to compute the extreme-UV SED from the intrinsic Ly α flux in ∼100 Å bins from 100–1170 Å. The reconstructed Ly α profiles have 300 km…

ABSTRACT Inferences about the spatial density or phase-space structure of stellar populations in the Milky Way require a precise determination of the effective survey volume. The volume observed by surveys such as Gaia or near-infrared spectroscopic surveys, which have good coverage of the Galactic midplane region, is highly complex because of the abundant small-scale structure in the three-dimensional interstellar dust extinction. We introduce a novel framework for analyzing the importance of small-scale structure in the extinction. This formalism demonstrates that the spatially complex effect of extinction on the selection function of a pencil-beam or contiguous sky survey is equivalent to a low-pass filtering of the extinction-affected selection function with the smooth density field. We find that the angular resolution of current 3D extinction maps is sufficient for analyzing Gaia sub-samples of millions of stars. However, the current distance resolution is inadequate and needs to be improved by an order of magnitude, especially in the inner Galaxy. We also present a practical…

ABSTRACT According to the virial theorem, all gravitational systems in equilibrium sit on a plane in the three-dimensional parameter space defined by their mass, size, and second moment of the velocity tensor. While these quantities cannot be directly observed, there are suitable proxies: the luminosity L k , half-light radius R e , and dispersion . These proxies indeed lie on a very tight fundamental plane (FP). How do the black holes (BHs) in the centers of galaxies relate to the FP? Their masses are known to exhibit no strong correlation with total galaxy mass, but they do correlate weakly with bulge mass (when present), and extremely well with the velocity dispersion through the relation. These facts together imply that a tight plane must also exist defined by BH mass, total galaxy mass, and size. Here, I show that this is indeed the case using a heterogeneous set of 230 BHs. The sample includes BHs from zero to 10 billion solar masses and host galaxies ranging from low surface brightness dwarfs, through bulgeless disks, to brightest cluster galaxies. The resulting…

ABSTRACT Transient detection and flux measurement via image subtraction stand at the base of time domain astronomy. Due to the varying seeing conditions, the image subtraction process is non-trivial, and existing solutions suffer from a variety of problems. Starting from basic statistical principles, we develop the optimal statistic for transient detection, flux measurement, and any image-difference hypothesis testing. We derive a closed-form statistic that: (1) is mathematically proven to be the optimal transient detection statistic in the limit of background-dominated noise, (2) is numerically stable, (3) for accurately registered, adequately sampled images, does not leave subtraction or deconvolution artifacts, (4) allows automatic transient detection to the theoretical sensitivity limit by providing credible detection significance, (5) has uncorrelated white noise, (6) is a sufficient statistic for any further statistical test on the difference image, and, in particular, allows us to distinguish particle hits and other image artifacts from real transients, (7) is symmetric to…

ABSTRACT We present cosmological parameter constraints obtained from galaxy clusters identified by their Sunyaev–Zel’dovich effect signature in the 2500 square-degree South Pole Telescope Sunyaev Zel’dovich (SPT-SZ) survey. We consider the 377 cluster candidates identified at with a detection significance greater than five, corresponding to the 95% purity threshold for the survey. We compute constraints on cosmological models using the measured cluster abundance as a function of mass and redshift. We include additional constraints from multi-wavelength observations, including Chandra X-ray data for 82 clusters and a weak lensing-based prior on the normalization of the mass-observable scaling relations. Assuming a spatially flat ΛCDM cosmology, we combine the cluster data with a prior on H 0 and find and , with the parameter combination . These results are in good agreement with constraints from the cosmic microwave background (CMB) from SPT, WMAP, and Planck, as well as with constraints from other cluster data sets. We also consider several extensions to ΛCDM, including models in…

ABSTRACT We present relativistic analyses of 9257 measurements of times-of-arrival from the first binary pulsar, PSR B1913+16, acquired over the last 35 years. The determination of the “Keplerian” orbital elements plus two relativistic terms completely characterizes the binary system, aside from an unknown rotation about the line of sight, leading to a determination of the masses of the pulsar and its companion: 1.438 ± 0.001 M ☉ and 1.390 ± 0.001 M ☉, respectively. In addition, the complete system characterization allows for the creation of relativistic gravitation test by comparing measured and predicted sizes of various relativistic phenomena. We find that the ratio of the observed orbital period decrease caused by gravitational wave damping (corrected by a kinematic term) to the general relativistic prediction is 0.9983 ± 0.0016, thereby confirms the existence and strength of gravitational radiation as predicted by general relativity. For the first time in this system, we have also successfully measured the two parameters characterizing the Shapiro gravitational propagation…

ABSTRACT The observed relation between the soft X-ray and the optical-ultraviolet emission in active galactic nuclei (AGNs) is nonlinear and it is usually parametrized as a dependence between the logarithm of the monochromatic luminosity at 2500 Å and at 2 keV. Previous investigations have found that the dispersion of this relation is rather high (∼0.35–0.4 in log units), which may be caused by measurement uncertainties, variability, and intrinsic dispersion due to differences in the AGN physical properties (e.g., different accretion modes). We show that, once optically selected quasars with homogeneous SED and X-ray detection are selected, and dust reddened and/or gas obscured objects are not included, the measured dispersion drops to significantly lower values (i.e., ∼0.21–0.24 dex). We show that the residual dispersion is due to some extent to variability, and to remaining measurement uncertainties. Therefore, the real physical intrinsic dispersion should be dex. Such a tight relation, valid over four decades in luminosity, must be the manifestation of an intrinsic (and…

ABSTRACT Roth et al. (2014a) reported evidence for plumes of water venting from a southern high latitude region on Europa: spectroscopic detection of off-limb line emission from the dissociation products of water. Here, we present Hubble Space Telescope direct images of Europa in the far-ultraviolet (FUV) as it transited the smooth face of Jupiter to measure absorption from gas or aerosols beyond the Europa limb. Out of 10 observations, we found 3 in which plume activity could be implicated. Two observations showed statistically significant features at latitudes similar to Roth et al., and the third at a more equatorial location. We consider potential systematic effects that might influence the statistical analysis and create artifacts, and are unable to find any that can definitively explain the features, although there are reasons to be cautious. If the apparent absorption features are real, the magnitude of implied outgassing is similar to that of the Roth et al. feature; however, the apparent activity appears more frequently in our data.

ABSTRACT We present H α maps at 1 kpc spatial resolution for star-forming galaxies at z ∼ 1, made possible by the Wide Field Camera 3 grism on Hubble Space Telescope ( HST ). Employing this capability over all five 3D- HST /CANDELS fields provides a sample of 3200 galaxies enabling a division into subsamples based on stellar mass and star formation rate (SFR). By creating deep stacked H α images, we reach surface brightness limits of 1 × 10 −18 erg s −1 cm −2 arcsec −2 , allowing us to map the distribution of ionized gas to ∼10 kpc for typical L * galaxies at this epoch. We find that the spatial extent of the H α distribution increases with stellar mass as kpc. The H α emission is more extended than the stellar continuum emission, consistent with inside-out assembly of galactic disks. This effect grows stronger with mass as . We map the H α distribution as a function of SFR(IR+UV) and find evidence for “coherent star formation” across the SFR– M * plane: above the main sequence (MS), H α is enhanced at all radii; below the MS, H α is depressed at all radii. This suggests that at all…

ABSTRACT Giant exoplanets orbiting very close to their parent star (hot Jupiters) are subject to tidal forces expected to synchronize their rotational and orbital periods on short timescales (tidal locking). However, spin rotation has never been measured directly for hot Jupiters. Furthermore, their atmospheres can show equatorial super-rotation via strong eastward jet streams, and/or high-altitude winds flowing from the day- to the night-side hemisphere. Planet rotation and atmospheric circulation broaden and distort the planet spectral lines to an extent that is detectable with measurements at high spectral resolution. We observed a transit of the hot Jupiter HD 189733 b around 2.3 μm and at a spectral resolution of R∼105 with CRIRES at the ESO Very Large Telescope. After correcting for the stellar absorption lines and their distortion during transit (the Rossiter–McLaughlin effect), we detect the absorption of carbon monoxide and water vapor in the planet transmission spectrum by cross-correlating with model spectra. The signal is maximized (7.6σ) for a planet rotational velocity…

ABSTRACT We present a new version of the MURaM radiative magnetohydrodynamics (MHD) code that allows for simulations spanning from the upper convection zone into the solar corona. We implement the relevant coronal physics in terms of optically thin radiative loss, field aligned heat conduction, and an equilibrium ionization equation of state. We artificially limit the coronal Alfvén and heat conduction speeds to computationally manageable values using an approximation to semi-relativistic MHD with an artificially reduced speed of light (Boris correction). We present example solutions ranging from quiet to active Sun in order to verify the validity of our approach. We quantify the role of numerical diffusivity for the effective coronal heating. We find that the (numerical) magnetic Prandtl number determines the ratio of resistive to viscous heating and that owing to the very large magnetic Prandtl number of the solar corona, heating is expected to happen predominantly through viscous dissipation. We find that reasonable solutions can be obtained with values of the reduced speed of…

ABSTRACT We compare evolutionary predictions of double compact object merger rate densities with initial and forthcoming LIGO/Virgo upper limits. We find that: (i) Due to the cosmological reach of advanced detectors, current conversion methods of population synthesis predictions into merger rate densities are insufficient. (ii) Our optimistic models are a factor of 18 below the initial LIGO/Virgo upper limits for BH–BH systems, indicating that a modest increase in observational sensitivity (by a factor of ∼2.5) may bring the first detections or first gravitational wave constraints on binary evolution. (iii) Stellar-origin massive BH–BH mergers should dominate event rates in advanced LIGO/Virgo and can be detected out to redshift z ≃ 2 with templates including inspiral, merger, and ringdown. Normal stars ( ) can produce such mergers with total redshifted mass up to . (iv) High black hole (BH) natal kicks can severely limit the formation of massive BH–BH systems (both in isolated binary and in dynamical dense cluster evolution), and thus would eliminate detection of these systems even…

ABSTRACT Supernovae (SNe) embedded in dense circumstellar material (CSM) may show prominent emission lines in their early-time spectra (≤10 days after the explosion), owing to recombination of the CSM ionized by the shock-breakout flash. From such spectra (“flash spectroscopy”), we can measure various physical properties of the CSM, as well as the mass-loss rate of the progenitor during the year prior to its explosion. Searching through the Palomar Transient Factory (PTF and iPTF) SN spectroscopy databases from 2009 through 2014, we found 12 SNe II showing flash-ionized (FI) signatures in their first spectra. All are younger than 10 days. These events constitute 14% of all 84 SNe in our sample having a spectrum within 10 days from explosion, and 18% of SNe II observed at ages <5 days, thereby setting lower limits on the fraction of FI events. We classified as “blue/featureless” (BF) those events having a first spectrum that is similar to that of a blackbody, without any emission or absorption signatures. It is possible that some BF events had FI signatures at an earlier phase than…

ABSTRACT The dust extinction curve is a critical component of many observational programs and an important diagnostic of the physics of the interstellar medium. Here we present new measurements of the dust extinction curve and its variation toward tens of thousands of stars, a hundred-fold larger sample than in existing detailed studies. We use data from the APOGEE spectroscopic survey in combination with ten-band photometry from Pan-STARRS1, the Two Micron All-Sky Survey, and Wide-field Infrared Survey Explorer. We find that the extinction curve in the optical through infrared is well characterized by a one-parameter family of curves described by R(V). The extinction curve is more uniform than suggested in past works, with σ ( R ( V ) ) = 0.18 , and with less than one percent of sight lines having R ( V ) > 4 . Our data and analysis have revealed two new aspects of Galactic extinction: first, we find significant, wide-area variations in R(V) throughout the Galactic plane. These variations are on scales much larger than individual molecular clouds, indicating that R(V) variations…

ABSTRACT Images of the linear polarizations of synchrotron radiation around active galactic nuclei (AGNs) highlight their projected magnetic field lines and provide key data for understanding the physics of accretion and outflow from supermassive black holes. The highest-resolution polarimetric images of AGNs are produced with Very Long Baseline Interferometry (VLBI). Because VLBI incompletely samples the Fourier transform of the source image, any image reconstruction that fills in unmeasured spatial frequencies will not be unique and reconstruction algorithms are required. In this paper, we explore some extensions of the Maximum Entropy Method (MEM) to linear polarimetric VLBI imaging. In contrast to previous work, our polarimetric MEM algorithm combines a Stokes I imager that only uses bispectrum measurements that are immune to atmospheric phase corruption, with a joint Stokes Q and U imager that operates on robust polarimetric ratios. We demonstrate the effectiveness of our technique on 7 and 3 mm wavelength quasar observations from the VLBA and simulated 1.3 mm Event Horizon…

ABSTRACT Hierarchical triple-star systems are expected to form frequently via close binary–binary encounters in the dense cores of globular clusters (GCs). In a sufficiently inclined triple, gravitational interactions between the inner and outer binary can cause large-amplitude oscillations in the eccentricity of the inner orbit (“Lidov–Kozai (LK) cycles”), which can lead to a collision and merger of the two inner components. In this paper we use Monte Carlo models of dense star clusters to identify all triple systems formed dynamically and we compute their evolution using a highly accurate three-body integrator which incorporates relativistic and tidal effects. We find that a large fraction of these triples evolve through a non-secular dynamical phase which can drive the inner binary to higher eccentricities than predicted by the standard secular perturbation theory (even including octupole-order terms). We place constraints on the importance of LK-induced mergers for producing: (i) gravitational wave sources detectable by Advanced LIGO (aLIGO), for triples with an inner pair of…

ABSTRACT The FourStar galaxy evolution survey (ZFOURGE) is a 45 night legacy program with the FourStar near-infrared camera on Magellan and one of the most sensitive surveys to date. ZFOURGE covers a total of 400 arcmin 2 in cosmic fields CDFS, COSMOS and UDS, overlapping CANDELS. We present photometric catalogs comprising >70,000 galaxies, selected from ultradeep K s -band detection images (25.5–26.5 AB mag, 5 σ , total), and >80% complete to K s < 25.3–25.9 AB. We use 5 near-IR medium-bandwidth filters ( J 1 , J 2 , J 3 , H s , H l ) as well as broad-band K s at 1.05–2.16 μ m to 25–26 AB at a seeing of ∼0.″5. Each field has ancillary imaging in 26–40 filters at 0.3–8 μ m. We derive photometric redshifts and stellar population properties. Comparing with spectroscopic redshifts indicates a photometric redshift uncertainty σ z = 0.010, 0.009, and 0.011 in CDFS, COSMOS, and UDS. As spectroscopic samples are often biased toward bright and blue sources, we also inspect the photometric redshift differences between close pairs of galaxies, finding σ z ,pairs = 0.01–0.02 at 1 < z < 2.5. We…

ABSTRACT We present a large, uniform analysis of young (≈10–150 Myr) ultracool dwarfs, based on new high-precision infrared (IR) parallaxes for 68 objects. We find that low-gravity ( vl-g ) late-M and L dwarfs form a continuous sequence in IR color–magnitude diagrams, separate from the field population and from current theoretical models. These vl-g objects also appear distinct from young substellar (brown dwarf and exoplanet) companions, suggesting that the two populations may have a different range of physical properties. In contrast, at the L/T transition, young, old, and spectrally peculiar objects all span a relatively narrow range in near-IR absolute magnitudes. At a given spectral type, the IR absolute magnitudes of young objects can be offset from ordinary field dwarfs, with the largest offsets occurring in the Y and J bands for late-M dwarfs (brighter than the field) and mid-/late-L dwarfs (fainter than the field). Overall, low-gravity ( vl-g ) objects have the most uniform photometric behavior, while intermediate gravity ( int-g ) objects are more diverse, suggesting a…

ABSTRACT As a long gamma-ray burst (GRB) jet propagates within the stellar atmosphere it creates a cocoon composed of an outer Newtonian shocked stellar material and an inner (possibly relativistic) shocked jet. The jet deposits erg into this cocoon. This is comparable to the energies of the GRB and of the accompanying supernova, yet the cocoon’s signature has been largely ignored. The cocoon radiates a fraction of this energy as it expands, following the breakout from the star, and later as it interacts with the surrounding matter. We explore the possible signatures of this emission and outline a framework to calculate them from the conditions of the cocoon at the time of the jet breakout. The cocoon signature depends strongly on the, currently unknown, mixing between the shocked jet and shocked stellar material. With no mixing the γ-ray emission from the cocoon is so bright that it should have been already detected. The lack of such detections indicates that some mixing must take place. For partial and full mixing the expected signals are weaker than regular GRB afterglows.…

ABSTRACT The evolution of the number density of galaxies in the universe, and thus also the total number of galaxies, is a fundamental question with implications for a host of astrophysical problems including galaxy evolution and cosmology. However, there has never been a detailed study of this important measurement, nor a clear path to answer it. To address this we use observed galaxy stellar mass functions up to z ∼ 8 to determine how the number densities of galaxies change as a function of time and mass limit. We show that the increase in the total number density of galaxies (ϕ T), more massive than M * = 106 M ⊙, decreases as ϕ T ∼ t −1, where t is the age of the universe. We further show that this evolution turns over and rather increases with time at higher mass lower limits of M * > 107 M ⊙. By using the M * = 106 M ⊙ lower limit we further show that the total number of galaxies in the universe up to z = 8 is (2 trillion), almost a factor of 10 higher than would be seen in an all sky survey at Hubble Ultra-Deep Field depth. We discuss the implications for these results for…

ABSTRACT Solar flares produce radiation that can have an almost immediate effect on the near-Earth environment, making it crucial to forecast flares in order to mitigate their negative effects. The number of published approaches to flare forecasting using photospheric magnetic field observations has proliferated, with varying claims about how well each works. Because of the different analysis techniques and data sets used, it is essentially impossible to compare the results from the literature. This problem is exacerbated by the low event rates of large solar flares. The challenges of forecasting rare events have long been recognized in the meteorology community, but have yet to be fully acknowledged by the space weather community. During the interagency workshop on “all clear” forecasts held in Boulder, CO in 2009, the performance of a number of existing algorithms was compared on common data sets, specifically line-of-sight magnetic field and continuum intensity images from the Michelson Doppler Imager, with consistent definitions of what constitutes an event. We demonstrate the…

ABSTRACT The mass of a star is arguably its most fundamental parameter. For red giant stars, tracers luminous enough to be observed across the Galaxy, mass implies a stellar evolution age. It has proven to be extremely difficult to infer ages and masses directly from red giant spectra using existing methods. From the Kepler and apogee surveys, samples of several thousand stars exist with high-quality spectra and asteroseismic masses. Here we show that from these data we can build a data-driven spectral model using The Cannon , which can determine stellar masses to ∼0.07 dex from apogee dr12 spectra of red giants; these imply age estimates accurate to ∼0.2 dex (40%). We show that The Cannon constrains these ages foremost from spectral regions with CN absorption lines, elements whose surface abundances reflect mass-dependent dredge-up. We deliver an unprecedented catalog of 70,000 giants (including 20,000 red clump stars) with mass and age estimates, spanning the entire disk (from the Galactic center to kpc). We show that the age information in the spectra is not simply a corollary of…

ABSTRACT We examine the internal consistency of the Planck 2015 cosmic microwave background (CMB) temperature anisotropy power spectrum. We show that tension exists between cosmological constant cold dark matter ( ) model parameters inferred from multipoles (roughly those accessible to Wilkinson Microwave Anisotropy Probe), and from , particularly the CDM density, , which is discrepant at for a Planck -motivated prior on the optical depth, . We find some parameter tensions to be larger than previously reported because of inaccuracy in the code used by the Planck Collaboration to generate model spectra. The Planck constraints are also in tension with low-redshift data sets, including Planck ’s own measurement of the CMB lensing power spectrum ( ), and the most precise baryon acoustic oscillation scale determination ( ). The Hubble constant predicted by Planck from , km s Mpc−1, disagrees with the most precise local distance ladder measurement of km s Mpc−1 at the level, while the Planck value from , km s Mpc−1, is consistent within . A discrepancy between the Planck and South Pole…

ABSTRACT Sub-Neptune-sized exoplanets represent the most common types of planets in the Milky Way, yet many of their properties are unknown. Here, we present a prescription to adapt the capabilities of the stellar evolution toolkit Modules for Experiments in Stellar Astrophysics to model sub-Neptune-mass planets with H/He envelopes. With the addition of routines treating the planet core luminosity, heavy-element enrichment, atmospheric boundary condition, and mass-loss due to hydrodynamic winds, the evolutionary pathways of planets with diverse starting conditions are more accurately constrained. Using these dynamical models, we construct mass-composition relationships of planets from 1–400 M ⊕ and investigate how mass-loss impacts their composition and evolution history. We demonstrate that planet radii are typically insensitive to the evolution pathway that brought the planet to its instantaneous mass, composition and age, with variations from hysteresis . We find that planet envelope mass-loss timescales, , vary non-monotonically with H/He envelope mass fractions (at fixed planet…

ABSTRACT Terrestrial planets at the inner edge of the habitable zone (HZ) of late-K and M-dwarf stars are expected to be in synchronous rotation, as a consequence of strong tidal interactions with their host stars. Previous global climate model (GCM) studies have shown that, for slowly rotating planets, strong convection at the substellar point can create optically thick water clouds, increasing the planetary albedo, and thus stabilizing the climate against a thermal runaway. However these studies did not use self-consistent orbital/rotational periods for synchronously rotating planets placed at different distances from the host star. Here we provide new estimates of the inner edge of the HZ for synchronously rotating terrestrial planets around late-K and M-dwarf stars using a 3D Earth-analog GCM with self-consistent relationships between stellar metallicity, stellar effective temperature, and the planetary orbital/rotational period. We find that both atmospheric dynamics and the efficacy of the substellar cloud deck are sensitive to the precise rotation rate of the planet. Around…

ABSTRACT We report the discovery of a remarkable concentration of massive galaxies with extended X-ray emission at z spec = 2.506, which contains 11 massive ( M * ≳ 10 11 M ⊙ ) galaxies in the central 80 kpc region (11.6 σ overdensity). We have spectroscopically confirmed 17 member galaxies with 11 from CO and the remaining ones from H α . The X-ray luminosity, stellar mass content, and velocity dispersion all point to a collapsed, cluster-sized dark matter halo with mass M 200 c = 10 13.9±0.2 M ⊙ , making it the most distant X-ray-detected cluster known to date. Unlike other clusters discovered so far, this structure is dominated by star-forming galaxies (SFGs) in the core with only 2 out of the 11 massive galaxies classified as quiescent. The star formation rate (SFR) in the 80 kpc core reaches ∼3400 M ⊙ yr −1 with a gas depletion time of ∼200 Myr, suggesting that we caught this cluster in rapid build-up of a dense core. The high SFR is driven by both a high abundance of SFGs and a higher starburst fraction (∼25%, compared to 3%–5% in the field). The presence of both a collapsed,…

ABSTRACT We present a catalog of panchromatic spectral energy distributions (SEDs) for 7 M and 4 K dwarf stars that span X-ray to infrared wavelengths (5 Å –5.5 μ m). These SEDs are composites of Chandra or XMM-Newton data from 5–∼50 Å, a plasma emission model from ∼50–100 Å, broadband empirical estimates from 100–1170 Å, Hubble Space Telescope data from 1170–5700 Å, including a reconstruction of stellar Ly α emission at 1215.67 Å, and a PHOENIX model spectrum from 5700–55000 Å. Using these SEDs, we computed the photodissociation rates of several molecules prevalent in planetary atmospheres when exposed to each star’s unattenuated flux (“unshielded” photodissociation rates) and found that rates differ among stars by over an order of magnitude for most molecules. In general, the same spectral regions drive unshielded photodissociations both for the minimally and maximally FUV active stars. However, for O 3 visible flux drives dissociation for the M stars whereas near-UV flux drives dissociation for the K stars. We also searched for an far-UV continuum in the assembled SEDs and…

ABSTRACT We present the rationale for and the observational description of ASPECS: the ALMA SPECtroscopic Survey in the Hubble Ultra-Deep Field (UDF), the cosmological deep field that has the deepest multi-wavelength data available. Our overarching goal is to obtain an unbiased census of molecular gas and dust continuum emission in high-redshift ( z > 0.5) galaxies. The ∼1′ region covered within the UDF was chosen to overlap with the deepest available imaging from the Hubble Space Telescope . Our ALMA observations consist of full frequency scans in band 3 (84–115 GHz) and band 6 (212–272 GHz) at approximately uniform line sensitivity ( 2 × 10 9 K km s −1 pc 2 ), and continuum noise levels of 3.8 μ Jy beam −1 and 12.7 μ Jy beam −1 , respectively. The molecular surveys cover the different rotational transitions of the CO molecule, leading to essentially full redshift coverage. The [C ii ] emission line is also covered at redshifts . We present a customized algorithm to identify line candidates in the molecular line scans and quantify our ability to recover artificial sources from our…

ABSTRACT We present ultraviolet through near-infrared photometry and spectroscopy of the host galaxies of all superluminous supernovae (SLSNe) discovered by the Palomar Transient Factory prior to 2013 and derive measurements of their luminosities, star formation rates, stellar masses, and gas-phase metallicities. We find that Type I (hydrogen-poor) SLSNe (SLSNe I) are found almost exclusively in low-mass ( ) and metal-poor (12 + log 10 [O/H] ) galaxies. We compare the mass and metallicity distributions of our sample to nearby galaxy catalogs in detail and conclude that the rate of SLSNe I as a fraction of all SNe is heavily suppressed in galaxies with metallicities . Extremely low metallicities are not required and indeed provide no further increase in the relative SLSN rate. Several SLSN I hosts are undergoing vigorous starbursts, but this may simply be a side effect of metallicity dependence: dwarf galaxies tend to have bursty star formation histories. Type II (hydrogen-rich) SLSNe (SLSNe II) are found over the entire range of galaxy masses and metallicities, and their integrated…

ABSTRACT A global picture of the evolution of protoplanetary disks (PPDs) is key to understanding almost every aspect of planet formation, where standard α -disk models have been continually employed for their simplicity. In the meantime, disk mass loss has been conventionally attributed to photoevaporation, which controls disk dispersal. However, a paradigm shift toward accretion driven by magnetized disk winds has taken place in recent years, thanks to studies of non-ideal magnetohydrodynamic effects in PPDs. I present a framework of global PPD evolution aiming to incorporate these advances, highlighting the role of wind-driven accretion and wind mass loss. Disk evolution is found to be largely dominated by wind-driven processes, and viscous spreading is suppressed. The timescale of disk evolution is controlled primarily by the amount of external magnetic flux threading the disks, and how rapidly the disk loses the flux. Rapid disk dispersal can be achieved if the disk is able to hold most of its magnetic flux during the evolution. In addition, because wind launching requires a…

ABSTRACT We show that, for a low-mass planet that orbits its host star within a few tenths of an AU (like the majority of the Kepler planets), the atmosphere it was able to accumulate while embedded in the protoplanetary disk may not survive unscathed after the disk disperses. This gas envelope, if more massive than a few percent of the core (with a mass below ), has a cooling time that is much longer than the timescale on which the planet exits the disk. As such, it could not have contracted significantly from its original size, of the order of the Bondi radius. So a newly exposed protoplanet would be losing mass via a Parker wind that is catalyzed by the stellar continuum radiation. This represents an intermediate stage of mass-loss, occurring soon after the disk has dispersed, but before the EUV/X-ray driven photoevaporation becomes relevant. The surface mass-loss induces a mass movement within the envelope that advects internal heat outward. As a result, the planet atmosphere rapidly cools down and contracts, until it has reached a radius of the order of 0.1 Bondi radius, at…

ABSTRACT We present measurements of the evolution of normal-galaxy X-ray emission from 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 ( ) 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 ( ) and redshift, provide significantly improved characterizations of the average X-ray emission from normal galaxy populations at 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 and SFR, respectively. We find (LMXB)/ and…

ABSTRACT With current space-based missions it is now possible to obtain age-sensitive asteroseismic information for tens of thousands of red giants. This provides a promising opportunity to study the Galactic structure and evolution. We use asteroseismic data of red giants, observed by Kepler, to test the current theoretical framework of modeling the Galaxy based on population synthesis modeling and the use of asteroseismic scaling relations for giants. We use the open source code Galaxia to model the Milky Way and find the distribution of the masses predicted by Galaxia to be systematically offset with respect to the seismically inferred observed masses. The Galactic model overestimates the number of low-mass stars, and these stars are predominantly old and of low metallicity. Using corrections to the Δ ν scaling relation suggested by stellar models significantly reduces the disagreement between predicted and observed masses. For a few cases where non-seismic mass estimates are available, the corrections to Δ ν also improve the agreement between seismic and non-seismic mass…

ABSTRACT We present a comprehensive analysis of strong-lensing, weak-lensing shear and magnification data for a sample of 16 X-ray-regular and 4 high-magnification galaxy clusters at 0.19 ≲ z ≲ 0.69 selected from Cluster Lensing And Supernova survey with Hubble (CLASH). Our analysis combines constraints from 16-band Hubble Space Telescope observations and wide-field multi-color imaging taken primarily with Suprime-Cam on the Subaru Telescope, spanning a wide range of cluster radii (10″–16′). We reconstruct surface mass density profiles of individual clusters from a joint analysis of the full lensing constraints, and determine masses and concentrations for all of the clusters. We find the internal consistency of the ensemble mass calibration to be ≤5% ± 6% in the one-halo regime (200–2000 kpc h −1) compared to the CLASH weak-lensing-only measurements of Umetsu et al. For the X-ray-selected subsample of 16 clusters, we examine the concentration–mass (c–M) relation and its intrinsic scatter using a Bayesian regression approach. Our model yields a mean concentration of c ∣ z = 0.34 =…

ABSTRACT We report the discovery of 15 quasars and bright galaxies at 5.7 < z < 6.9. This is the initial result from the Subaru High-z Exploration of Low-Luminosity Quasars project, which exploits the exquisite multiband imaging data produced by the Subaru Hyper Suprime-Cam (HSC) Strategic Program survey. The candidate selection is performed by combining several photometric approaches including a Bayesian probabilistic algorithm to reject stars and dwarfs. The spectroscopic identification was carried out with the Gran Telescopio Canarias and the Subaru Telescope for the first 80 deg2 of the survey footprint. The success rate of our photometric selection is quite high, approaching 100% at the brighter magnitudes (z AB < 23.5 mag). Our selection also recovered all the known high-z quasars on the HSC images. Among the 15 discovered objects, six are likely quasars, while the other six with interstellar absorption lines and in some cases narrow emission lines are likely bright Lyman-break galaxies. The remaining three objects have weak continua and very strong and narrow Lyα lines, which…

ABSTRACT We study the emission from tidal disruption events (TDEs) produced as radiation from black hole accretion propagates through an extended, optically thick envelope formed from stellar debris. We analytically describe key physics controlling spectrum formation, and present detailed radiative transfer calculations that model the spectral energy distribution and optical line strengths of TDEs near peak brightness. The steady-state transfer is coupled to a solver for the excitation and ionization states of hydrogen, helium, and oxygen (as a representative metal), without assuming local thermodynamic equilibrium. Our calculations show how an extended envelope can reprocess a fraction of soft X-rays and produce the observed optical fluxes of the order of 1043 erg s−1, with an optical/UV continuum that is not described by a single blackbody. Variations in the mass or size of the envelope may help explain how the optical flux changes over time with roughly constant color. For high enough accretion luminosities, X-rays can escape to be observed simultaneously with the optical flux.…

ABSTRACT We present coupled stellar evolution (SE) and 3D radiation-hydrodynamic (RHD) simulations of the evolution of primordial protostars, their immediate environment, and the dynamic accretion history under the influence of stellar ionizing and dissociating UV feedback. Our coupled SE RHD calculations result in a wide diversity of final stellar masses covering 10 ≲ M * ≲ 103 . The formation of very massive (≳250 ) stars is possible under weak UV feedback, whereas ordinary massive (a few ×10 ) stars form when UV feedback can efficiently halt the accretion. This may explain the peculiar abundance pattern of a Galactic metal-poor star recently reported by Aoki et al., possibly the observational signature of very massive precursor primordial stars. Weak UV feedback occurs in cases of variable accretion, in particular when repeated short accretion bursts temporarily exceed 0.01 , causing the protostar to inflate. In the bloated state, the protostar has low surface temperature and UV feedback is suppressed until the star eventually contracts, on a thermal adjustment timescale, to…

ABSTRACT In this paper, we investigate the level of hydrostatic equilibrium (HE) in the intracluster medium of simulated galaxy clusters, extracted from state-of-the-art cosmological hydrodynamical simulations performed with the Smoothed-Particle-Hydrodynamic code GADGET-3. These simulations include several physical processes, among which are stellar and active galactic nucleus feedback, and have been performed with an improved version of the code that allows for a better description of hydrodynamical instabilities and gas mixing processes. Evaluating the radial balance between the gravitational and hydrodynamical forces via the gas accelerations generated, we effectively examine the level of HE in every object of the sample and its dependence on the radial distance from the center and on the classification of the cluster in terms of either cool-coreness or dynamical state. We find an average deviation of 10%–20% out to the virial radius, with no evident distinction between cool-core and non-cool-core clusters. Instead, we observe a clear separation between regular and disturbed…

ABSTRACT We identify four unusually bright (H < 25.5) galaxies from Hubble Space Telescope (HST) and Spitzer CANDELS data with probable redshifts z ∼ 7–9. These identifications include the brightest-known galaxies to date at z ≳ 7.5. As Y-band observations are not available over the full CANDELS program to perform a standard Lyman-break selection of z > 7 galaxies, we employ an alternate strategy using deep Spitzer/IRAC data. We identify z ∼ 7.1–9.1 galaxies by selecting z ≳ 6 galaxies from the HST CANDELS data that show quite red IRAC [3.6]−[4.5] colors, indicating strong [O iii]+Hβ lines in the 4.5 μm band. This selection strategy was validated using a modest sample for which we have deep Y-band coverage, and subsequently used to select the brightest z ≥ 7 sources. Applying the IRAC criteria to all HST-selected optical dropout galaxies over the full ∼900 arcmin2 of the CANDELS survey revealed four unusually bright z ∼ 7.1, 7.6, 7.9, and 8.6 candidates. The median [3.6]−[4.5] color of our selected z ∼ 7.1–9.1 sample is consistent with rest-frame [O iii]+Hβ EWs of ∼1500 Å in the…

ABSTRACT The spatial structure of stellar populations with different chemical abundances in the Milky Way (MW) contains a wealth of information on Galactic evolution over cosmic time. We use data on 14,699 red-clump stars from the APOGEE survey, covering , to determine the structure of mono-abundance populations (MAPs)—stars in narrow bins in and —accounting for the complex effects of the APOGEE selection function and the spatially variable dust obscuration. We determine that all MAPs with enhanced are centrally concentrated and are well-described as exponentials with a scale length of over the whole radial range of the disk. We discover that the surface-density profiles of low- MAPs are complex: they do not monotonically decrease outwards, but rather display a peak radius ranging from to at low . The extensive radial coverage of the data allows us to measure radial trends in the thickness of each MAP. While high- MAPs have constant scale heights, low- MAPs flare. We confirm, now with high-precision abundances, previous results that each MAP contains only a single vertical scale…

ABSTRACT We report the analysis of two new spectroscopic observations in the near-infrared of the super-Earth 55 Cancri e, obtained with the WFC3 camera on board the Hubble Space Telescope. 55 Cancri e orbits so close to its parent star that temperatures much higher than 2000 K are expected on its surface. Given the brightness of 55 Cancri, the observations were obtained in scanning mode, adopting a very long scanning length and a very high scanning speed. We use our specialized pipeline to take into account systematics introduced by these observational parameters when coupled with the geometrical distortions of the instrument. We measure the transit depth per wavelength channel with an average relative uncertainty of 22 ppm per visit and find modulations that depart from a straight line model with a 6σ confidence level. These results suggest that 55 Cancri e is surrounded by an atmosphere, which is probably hydrogen-rich. Our fully Bayesian spectral retrieval code, -REx, has identified HCN to be the most likely molecular candidate able to explain the features at 1.42 and 1.54 μm.…

ABSTRACT We model the impact of nonuniform cloud cover on transit transmission spectra. Patchy clouds exist in nearly every solar system atmosphere, brown dwarfs, and transiting exoplanets. Our major findings suggest that fractional cloud coverage can exactly mimic high mean molecular weight atmospheres and vice versa over certain wavelength regions, in particular, over the Hubble Space Telescope ( HST ) Wide Field Camera 3 (WFC3) bandpass (1.1–1.7 μ m). We also find that patchy cloud coverage exhibits a signature that is different from uniform global clouds. Furthermore, we explain analytically why the “patchy cloud-high mean molecular weight” degeneracy exists. We also explore the degeneracy of nonuniform cloud coverage in atmospheric retrievals on both synthetic and real planets. We find from retrievals on a synthetic solar composition hot Jupiter with patchy clouds and a cloud-free high mean molecular weight warm Neptune that both cloud-free high mean molecular weight atmospheres and partially cloudy atmospheres can explain the data equally well. Another key finding is that the…

ABSTRACT We present a new, publicly available set of Los Alamos OPLIB opacity tables for the elements hydrogen through zinc. Our tables are computed using the Los Alamos ATOMIC opacity and plasma modeling code, and make use of atomic structure calculations that use fine-structure detail for all the elements considered. Our equation of state model, known as ChemEOS, is based on the minimization of free energy in a chemical picture and appears to be a reasonable and robust approach to determining atomic state populations over a wide range of temperatures and densities. In this paper we discuss in detail the calculations that we have performed for the 30 elements considered, and present some comparisons of our monochromatic opacities with measurements and other opacity codes. We also use our new opacity tables in solar modeling calculations and compare and contrast such modeling with previous work.

ABSTRACT Turbulence is ubiquitous in molecular clouds (MCs), but its origin is still unclear because MCs are usually assumed to live longer than the turbulence dissipation time. Interstellar medium (ISM) turbulence is likely driven by supernova (SN) explosions, but it has never been demonstrated that SN explosions can establish and maintain a turbulent cascade inside MCs consistent with the observations. In this work, we carry out a simulation of SN-driven turbulence in a volume of (250 pc) 3 , specifically designed to test if SN driving alone can be responsible for the observed turbulence inside MCs. We find that SN driving establishes a velocity scaling consistent with the usual scaling laws of supersonic turbulence, suggesting that previous idealized simulations of MC turbulence, driven with a random, large-scale volume force, were correctly adopted as appropriate models for MC turbulence, despite the artificial driving. We also find that the same scaling laws extend to the interiors of MCs, and that the velocity–size relation of the MCs selected from our simulation is consistent…

ABSTRACT The total contribution of diffuse halo gas to the galaxy baryon budget strongly depends on its dominant ionization state. In this paper, we address the physical conditions in the highly ionized circumgalactic medium (CGM) traced by absorption lines observed in COS-Halos spectra. We analyze the observed ionic column densities, absorption-line widths and relative velocities, along with the ratios of / for 39 fitted Voigt profile components of O vi. We compare these quantities with the predictions given by a wide range of ionization models. Photoionization models that include only extragalactic UV background radiation are ruled out; conservatively, the upper limits to / and measurements of imply unphysically large path lengths ≳100 kpc. Furthermore, very broad absorption (b > 40 km s−1) is a defining characteristic of the CGM of star-forming L* galaxies. We highlight two possible origins for the bulk of the observed : (1) highly structured gas clouds photoionized primarily by local high-energy sources or (2) gas radiatively cooling on large scales behind a supersonic wind.…