Showing papers in "The Astrophysical Journal in 2011"

Measuring Reddening with Sloan Digital Sky Survey Stellar Spectra and Recalibrating SFD

Abstract: We present measurements of dust reddening using the colors of stars with spectra in the Sloan Digital Sky Survey. We measure reddening as the difference between the measured and predicted colors of a star, as derived from stellar parameters from the Sloan Extension for Galactic Understanding and Exploration Stellar Parameter Pipeline. We achieve uncertainties of 56, 34, 25, and 29 mmag in the colors u – g, g – r, r – i, and i – z, per star, though the uncertainty varies depending on the stellar type and the magnitude of the star. The spectrum-based reddening measurements confirm our earlier "blue tip" reddening measurements, finding reddening coefficients different by –3%, 1%, 1%, and 2% in u – g, g – r, r – i, and i – z from those found by the blue tip method, after removing a 4% normalization difference. These results prefer an RV = 3.1 Fitzpatrick reddening law to O'Donnell or Cardelli et al. reddening laws. We provide a table of conversion coefficients from the Schlegel et al. (SFD) maps of E(B – V) to extinction in 88 bandpasses for four values of RV , using this reddening law and the 14% recalibration of SFD first reported by Schlafly et al. and confirmed in this work.

A 3% Solution: Determination of the Hubble Constant with the Hubble Space Telescope and Wide Field Camera 3

Abstract: We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to determine the Hubble constant from optical and infrared observations of over 600 Cepheid variables in the host galaxies of eight recent Type Ia supernovae (SNe Ia), providing the calibration for a magnitude-redshift relation based on 253 SNe Ia. Increased precision over past measurements of the Hubble constant comes from five improvements: (1) more than doubling the number of infrared observations of Cepheids in the nearby SN hosts; (2) increasing the sample size of ideal SN Ia calibrators from six to eight; (3) increasing by 20% the number of Cepheids with infrared observations in the megamaser host NGC 4258; (4) reducing the difference in the mean metallicity of the Cepheid comparison samples between NGC 4258 and the SN hosts from Δlog [O/H] = 0.08 to 0.05; and (5) calibrating all optical Cepheid colors with a single camera, WFC3, to remove cross-instrument zero-point errors. The result is a reduction in the uncertainty in H 0 due to steps beyond the first rung of the distance ladder from 3.5% to 2.3%. The measurement of H 0 via the geometric distance to NGC 4258 is 74.8 ± 3.1 km s–1 Mpc–1, a 4.1% measurement including systematic uncertainties. Better precision independent of the distance to NGC 4258 comes from the use of two alternative Cepheid absolute calibrations: (1) 13 Milky Way Cepheids with trigonometric parallaxes measured with HST/fine guidance sensor and Hipparcos and (2) 92 Cepheids in the Large Magellanic Cloud for which multiple accurate and precise eclipsing binary distances are available, yielding 74.4 ± 2.5 km s–1 Mpc–1, a 3.4% uncertainty including systematics. Our best estimate uses all three calibrations but a larger uncertainty afforded from any two: H 0 = 73.8 ± 2.4 km s–1 Mpc–1 including systematic errors, corresponding to a 3.3% uncertainty. The improved measurement of H 0, when combined with the Wilkinson Microwave Anisotropy Probe (WMAP) 7 year data, results in a tighter constraint on the equation-of-state parameter of dark energy of w = –1.08 ± 0.10. It also rules out the best-fitting gigaparsec-scale void models, posited as an alternative to dark energy. The combined H 0 + WMAP results yield N eff = 4.2 ± 0.7 for the number of relativistic particle species in the early universe, a low-significance excess for the value expected from the three known neutrino flavors.

Characteristics of planetary candidates observed by Kepler. II. Analysis of the first four months of data

Abstract: On 2011 February 1 the Kepler mission released data for 156,453 stars observed from the beginning of the science observations on 2009 May 2 through September 16. There are 1235 planetary candidates with transit-like signatures detected in this period. These are associated with 997 host stars. Distributions of the characteristics of the planetary candidates are separated into five class sizes: 68 candidates of approximately Earth-size (R_p < 1.25 R_⊕), 288 super-Earth-size (1.25 R_⊕ ≤ R_p < 2 R_⊕), 662 Neptune-size (2 R_⊕ ≤ R_p < 6 R_⊕), 165 Jupiter-size (6 R_⊕ ≤ R_p < 15 R_⊕), and 19 up to twice the size of Jupiter (15 R_⊕ ≤ R_p < 22 R_⊕). In the temperature range appropriate for the habitable zone, 54 candidates are found with sizes ranging from Earth-size to larger than that of Jupiter. Six are less than twice the size of the Earth. Over 74% of the planetary candidates are smaller than Neptune. The observed number versus size distribution of planetary candidates increases to a peak at two to three times the Earth-size and then declines inversely proportional to the area of the candidate. Our current best estimates of the intrinsic frequencies of planetary candidates, after correcting for geometric and sensitivity biases, are 5% for Earth-size candidates, 8% for super-Earth-size candidates, 18% for Neptune-size candidates, 2% for Jupiter-size candidates, and 0.1% for very large candidates; a total of 0.34 candidates per star. Multi-candidate, transiting systems are frequent; 17% of the host stars have multi-candidate systems, and 34% of all the candidates are part of multi-candidate systems.

Dark matter halos in the standard cosmological model: results from the bolshoi simulation

Abstract: Lambda Cold Dark Matter (?CDM) is now the standard theory of structure formation in the universe. We present the first results from the new Bolshoi dissipationless cosmological ?CDM simulation that uses cosmological parameters favored by current observations. The Bolshoi simulation was run in a volume 250 h ?1?Mpc on a side using ~8 billion particles with mass and force resolution adequate to follow subhalos down to the completeness limit of V circ = 50?km?s?1 maximum circular velocity. Using merger trees derived from analysis of 180 stored time steps we find the circular velocities of satellites before they fall into their host halos. Using excellent statistics of halos and subhalos (~10 million at every moment and ~50 million over the whole history) we present accurate approximations for statistics such as the halo mass function, the concentrations for distinct halos and subhalos, the abundance of halos as a function of their circular velocity, and the abundance and the spatial distribution of subhalos. We find that at high redshifts the concentration falls to a minimum value of about 4.0 and then rises for higher values of halo mass?a new result. We present approximations for the velocity and mass functions of distinct halos as a function of redshift. We find that while the Sheth-Tormen (ST) approximation for the mass function of halos found by spherical overdensity is quite accurate at low redshifts, the ST formula overpredicts the abundance of halos by nearly an order of magnitude by z = 10. We find that the number of subhalos scales with the circular velocity of the host halo as V 1/2 host, and that subhalos have nearly the same radial distribution as dark matter particles at radii 0.3-2 times the host halo virial radius. The subhalo velocity function N(> V sub) scales as V ?3 circ. Combining the results of Bolshoi and Via Lactea-II simulations, we find that inside the virial radius of halos with the number of satellites is N(> V sub) = (V sub/58 km s?1)?3 for satellite circular velocities in the range 4 km s?1 < V sub < 150 km s?1.

The Lesser Role of Starbursts in Star Formation at z = 2

Abstract: Two main modes of star formation are know to control the growth of galaxies: a relatively steady one in disk-like galaxies, defining a tight star formation rate (SFR)-stellar mass sequence, and a starburst mode in outliers to such a sequence which is generally interpreted as driven by merging. Such starburst galaxies are rare but have much higher SFRs, and it is of interest to establish the relative importance of these two modes. PACS/Herschel observations over the whole COSMOS and GOODS-South fields, in conjunction with previous optical/near-IR data, have allowed us to accurately quantify for the first time the relative contribution of the two modes to the global SFR density in the redshift interval 1.5 1000 M ☉ yr-1, off-sequence sources significantly contribute to the SFR density (46% ± 20%). We conclude that merger-driven starbursts play a relatively minor role in the formation of stars in galaxies, whereas they may represent a critical phase toward the quenching of star formation and morphological transformation in galaxies.

Galaxy Clustering in the Completed SDSS Redshift Survey: The Dependence on Color and Luminosity

Abstract: We measure the luminosity and color dependence of galaxy clustering in the largest-ever galaxy redshift survey, the main galaxy sample of the Sloan Digital Sky Survey (SDSS) Seventh Data Release (DR7). We focus on the projected correlation function wp(rp) of volume-limited samples, extracted from the parent sample of ∼ 700,000 galaxies over 8000 deg 2 , extending up to redshift of 0.25. We interpret our measurements using halo occupation distribution (HOD) modeling assuming aCDM cosmol- ogy (inflationary cold dark matter with a cosmological constant). The amplitude of wp(rp) grows slowly with luminosity for L L) × (�8/0.8) = 1.06 + 0.21(L/L∗) 1.12 , where L is the sample luminosity threshold. At fixed luminosity, redder galaxies exhibit a higher amplitude and steeper correlation function, a steady trend that runs through the "blue cloud" and "green valley" and continues across the "red sequence." The cross-correlation of red and blue galaxies is close to the geometric mean of their auto- correlations, dropping slightly below at rp 4L∗, but the lowest luminosity red galaxies (0.04−0.25L∗) show very strong clustering on small scales (rp < 2h −1 Mpc). Most of the observed trends can be naturally understood within theCDM+HOD framework. The growth of wp(rp) for higher luminosity galaxies reflects an overall shift in the mass scale of their host dark matter halos, in particular an increase in the minimum host halo mass Mmin. The mass at which a halo has, on average, one satellite galaxy brighter than L is M1 ≈ 17Mmin(L) over most of the luminosity range, with a smaller ratio above L∗. The growth and steepening of wp(rp) for redder galaxies reflects the increasing fraction of galaxies that are satellite systems in high mass halos instead of central systems in low mass halos, a trend that is especially marked at low luminosities. Our exten- sive measurements, provided in tabular form, will allow detailed tests of theoretical models of galaxy formation, a firm grounding of semi-empirical models of the galaxy population, and new constraints on cosmological parameters from combining real-space galaxy clustering with mass-sensitive statistics such as redshift-space distortions, cluster mass-to-light ratios, and galaxy-galaxy lensing. Subject headings: cosmology: observations — cosmology: theory — galaxies: distances and redshifts — galaxies: halos — galaxies: statistics — large-scale structure of universe

The Internal-collision-induced Magnetic Reconnection and Turbulence (ICMART) Model of Gamma-ray Bursts

Abstract: The recent Fermi observation of GRB 080916C shows that the bright photosphere emission associated with a putative fireball is missing, which suggests that the central engine likely launches a Poynting-flux-dominated (PFD) outflow. We propose a model of gamma-ray burst (GRB) prompt emission in the PFD regime, namely, the InternalCollision-induced MAgnetic Reconnection and Turbulence (ICMART) model. It is envisaged that the GRB central engine launches an intermittent, magnetically dominated wind, and that in the GRB emission region, the ejecta is still moderately magnetized (e.g., 1 σ 100). Similar to the internal shock (IS) model, the mini-shells interact internally at the radius RIS ∼ Γ 2 cΔt. Most of these early collisions, however, have little energy dissipation, but serve to distort the ordered magnetic field lines entrained in the ejecta. At a certain point, the distortion of magnetic field configuration reaches the critical condition to allow fast reconnection seeds to occur, which induce relativistic MHD turbulence in the interaction regions. The turbulence further distorts field lines easing additional magnetic reconnections, resulting in a runway release of the stored magnetic field energy (an ICMART event). Particles are accelerated either directly in the reconnection zone, or stochastically in the turbulent regions, which radiate synchrotron photons that power the observed gamma rays. Each ICMART event corresponds to a broad pulse in the GRB light curve, and a GRB is composed of multiple ICMART events. This model retains the merits of IS and other models, but may overcome several difficulties/issues faced by the IS model (e.g., low efficiency, fast cooling, electron number excess, Amati/Yonetoku relation inconsistency, and missing bright photosphere). Within this model, the observed GRB variability timescales could have two components, one slow component associated with the central engine time history, and another fast component associated with relativistic magnetic turbulence in the emission region. The model predicts a decrease of gamma-ray polarization degree and Ep in each ICMART event (broad pulse) during the prompt GRB phase, as well as a moderately magnetized external reverse shock. The model may be applied to the GRBs that have time-resolved, featureless Band-function spectra, such as GRB 080916C and most GRBs detected by Fermi LAT.

Resolved Images of Large Cavities in Protoplanetary Transition Disks

Abstract: Circumstellar disks are thought to experience a rapid transition phase in their evolution that can have a considerable impact on the formation and early development of planetary systems. We present new and archival high angular resolution (03 40-75 AU) Submillimeter Array (SMA) observations of the 880 μm (340 GHz) dust continuum emission from 12 such transition disks in nearby star-forming regions. In each case, we directly resolve a dust-depleted disk cavity around the central star. Using two-dimensional Monte Carlo radiative transfer calculations, we interpret these dust disk structures in a homogeneous, parametric model framework by reproducing their SMA continuum visibilities and spectral energy distributions. The cavities in these disks are large (R cav = 15-73 AU) and substantially depleted of small (~μm-sized) dust grains, although their mass contents are still uncertain. The structures of the remnant material at larger radii are comparable to normal disks. We demonstrate that these large cavities are relatively common among the millimeter-bright disk population, comprising at least 1 in 5 (20%) of the disks in the bright half (and ≥26% of the upper quartile) of the millimeter luminosity (disk mass) distribution. Utilizing these results, we assess some of the physical mechanisms proposed to account for transition disk structures. As has been shown before, photoevaporation models do not produce the large cavity sizes, accretion rates, and disk masses representative of this sample. A sufficient decrease of the dust optical depths in these cavities by particle growth would be difficult to achieve: substantial growth (to meter sizes or beyond) must occur in large (tens of AU) regions of low turbulence without also producing an abundance of small particles. Given those challenges, we suggest instead that the observations are most commensurate with dynamical clearing due to tidal interactions with low-mass companions—very young (~1 Myr) brown dwarfs or giant planets on long-period orbits.

Preliminary results from neowise: an enhancement to the wide-field infrared survey explorer for solar system science

Abstract: The Wide-field Infrared Survey Explorer (WISE) has surveyed the entire sky at four infrared wavelengths with greatly improved sensitivity and spatial resolution compared to its predecessors, the Infrared Astronomical Satellite and the Cosmic Background Explorer. NASA's Planetary Science Division has funded an enhancement to the WISE data processing system called "NEOWISE" that allows detection and archiving of moving objects found in the WISE data. NEOWISE has mined the WISE images for a wide array of small bodies in our solar system, including near-Earth objects (NEOs), Main Belt asteroids, comets, Trojans, and Centaurs. By the end of survey operations in 2011 February, NEOWISE identified over 157,000 asteroids, including more than 500 NEOs and ~120 comets. The NEOWISE data set will enable a panoply of new scientific investigations.

CALIBRATING EXTINCTION-FREE STAR FORMATION RATE DIAGNOSTICS WITH 33 GHz FREE-FREE EMISSION IN NGC 6946

Abstract: Using free-free emission measured in the Ka band (26-40 GHz) for 10 star-forming regions in the nearby galaxy NGC 6946, including its starbursting nucleus, we compare a number of star formation rate (SFR) diagnostics that are typically considered to be unaffected by interstellar extinction. These diagnostics include non-thermal radio (i.e., 1.4 GHz), total infrared (IR; 8-1000 μm), and warm dust (i.e., 24 μm) emission, along with hybrid indicators that attempt to account for obscured and unobscured emission from star-forming regions including Hα + 24 μm and UV + IR measurements. The assumption is made that the 33 GHz free-free emission provides the most accurate measure of the current SFR. Among the extranuclear star-forming regions, the 24 μm, Hα + 24 μm, and UV + IR SFR calibrations are in good agreement with the 33 GHz free-free SFRs. However, each of the SFR calibrations relying on some form of dust emission overestimates the nuclear SFR by a factor of ~2 relative to the 33 GHz free-free SFR. This is more likely the result of excess dust heating through an accumulation of non-ionizing stars associated with an extended episode of star formation in the nucleus rather than increased competition for ionizing photons by dust. SFR calibrations using the non-thermal radio continuum yield values which only agree with the 33 GHz free-free SFRs for the nucleus and underestimate the SFRs from the extranuclear star-forming regions by an average factor of ~2 and ~4-5 before and after subtracting local background emission, respectively. This result likely arises from the cosmic-ray (CR) electrons decaying within the starburst region with negligible escape, whereas the transient nature of star formation in the young extranuclear star-forming complexes allows for CR electrons to diffuse significantly further than dust-heating photons, resulting in an underestimate of the true SFR. Finally, we find that the SFRs estimated using the total 33 GHz flux density appear to agree well with those estimated using free-free emission due to the large thermal fractions present at these frequencies even when local diffuse backgrounds are not removed. Thus, rest-frame 33 GHz observations may act as a reliable method to measure the SFRs of galaxies at increasingly high redshift without the need of ancillary radio data to account for the non-thermal emission.

GALAXY STRUCTURE AND MODE OF STAR FORMATION IN THE SFR-MASS PLANE FROM z ∼ 2.5 TO z ∼ 0.1

Abstract: We analyze the dependence of galaxy structure (size and Sersic index) and mode of star formation (ΣSFR and SFRIR/SFRUV) on the position of galaxies in the star formation rate (SFR) versus mass diagram. Our sample comprises roughly 640,000 galaxies at z ~ 0.1, 130,000 galaxies at z ~ 1, and 36,000 galaxies at z ~ 2. Structural measurements for all but the z ~ 0.1 galaxies are based on Hubble Space Telescope imaging, and SFRs are derived using a Herschel-calibrated ladder of SFR indicators. We find that a correlation between the structure and stellar population of galaxies (i.e., a "Hubble sequence") is already in place since at least z ~ 2.5. At all epochs, typical star-forming galaxies on the main sequence are well approximated by exponential disks, while the profiles of quiescent galaxies are better described by de Vaucouleurs profiles. In the upper envelope of the main sequence, the relation between the SFR and Sersic index reverses, suggesting a rapid buildup of the central mass concentration in these starbursting outliers. We observe quiescent, moderately and highly star-forming systems to co-exist over an order of magnitude or more in stellar mass. At each mass and redshift, galaxies on the main sequence have the largest size. The rate of size growth correlates with specific SFR, and so does ΣSFR at each redshift. A simple model using an empirically determined star formation law and metallicity scaling, in combination with an assumed geometry for dust and stars, is able to relate the observed ΣSFR and SFRIR/SFRUV, provided a more patchy dust geometry is assumed for high-redshift galaxies.

The stellar activity-rotation relationship and the evolution of stellar dynamos

Abstract: We present a sample of 824 solar and late-type stars with X-ray luminosities and rotation periods. This is used to study the relationship between rotation and stellar activity and derive a new estimate of the convective turnover time. From an unbiased subset of this sample the power-law slope of the unsaturated regime, LX /L bolRo?, is fit as ? = ?2.70 ? 0.13. This is inconsistent with the canonical ? = ?2 slope to a confidence of 5?, and argues for an additional term in the dynamo number equation. From a simple scaling analysis this implies ??/??0.7, i.e., the differential rotation of solar-type stars gradually declines as they spin down. Supersaturation is observed for the fastest rotators in our sample and its parametric dependencies are explored. Significant correlations are found with both the corotation radius and the excess polar updraft, the latter theory providing a stronger dependence and being supported by other observations. We estimate mass-dependent empirical thresholds for saturation and supersaturation and map out three regimes of coronal emission. Late F-type stars are shown never to pass through the saturated regime, passing straight from supersaturated to unsaturated X-ray emission. The theoretical threshold for coronal stripping is shown to be significantly different from the empirical saturation threshold (Ro < 0.13), suggesting it is not responsible. Instead we suggest that a different dynamo configuration is at work in stars with saturated coronal emission. This is supported by a correlation between the empirical saturation threshold and the time when stars transition between convective and interface sequences in rotational spin-down models.

The Spitzer-WISE Survey of the Ecliptic Poles

Abstract: We have carried out a survey of the north and south ecliptic poles, EP-N and EP-S, respectively, with the Spitzer Space Telescope and the Wide-field Infrared Survey Explorer (WISE). The primary objective was to cross-calibrate WISE with the Spitzer and Midcourse Space Experiment (MSX) photometric systems by developing a set of calibration stars that are common to these infrared missions. The ecliptic poles were continuous viewing zones for WISE due to its polar-crossing orbit, making these areas ideal for both absolute and internal calibrations. The Spitzer IRAC and MIPS imaging survey covers a complete area of 0.40 deg^2 for the EP-N and 1.28 deg^2 for the EP-S. WISE observed the whole sky in four mid-infrared bands, 3.4, 4.6, 12, and 22 μm, during its eight-month cryogenic mission, including several hundred ecliptic polar passages; here we report on the highest coverage depths achieved by WISE, an area of ~1.5 deg^2 for both poles. Located close to the center of the EP-N, the Sy-2 galaxy NGC 6552 conveniently functions as a standard calibrator to measure the red response of the 22 μm channel of WISE. Observations from Spitzer-IRAC/MIPS/IRS-LL and WISE show that the galaxy has a strong red color in the mid-infrared due to star-formation and the presence of an active galactic nucleus (AGN), while over a baseline >1 year the mid-IR photometry of NGC 6552 is shown to vary at a level less than 2%. Combining NGC 6552 with the standard calibrator stars, the achieved photometric accuracy of the WISE calibration, relative to the Spitzer and MSX systems, is 2.4%, 2.8%, 4.5%, and 5.7% for W1 (3.4 μm), W2 (4.6 μm), W3 (12 μm), and W4 (22 μm), respectively. The WISE photometry is internally stable to better than 0.1% over the cryogenic lifetime of the mission. The secondary objective of the Spitzer-WISE Survey was to explore the poles at greater flux-level depths, exploiting the higher angular resolution Spitzer observations and the exceptionally deep (in total coverage) WISE observations that potentially reach down to the confusion limit of the survey. The rich Spitzer and WISE data sets were used to study the Galactic and extragalactic populations through source counts, color-magnitude and color-color diagrams. As an example of what the data sets facilitate, we have separated stars from galaxies, delineated normal galaxies from power-law-dominated AGNs, and reported on the different fractions of extragalactic populations. In the EP-N, we find an AGN source density of ~260 deg^(–2) to a 12 μm depth of 115 μJy, representing 15% of the total extragalactic population to this depth, similar to what has been observed for low-luminosity AGNs in other fields.

Ultraviolet Luminosity Functions from 132 z ~ 7 and z ~ 8 Lyman-break Galaxies in the Ultra-deep HUDF09 and Wide-area Early Release Science WFC3/IR Observations

Abstract: We identify 73 z ~ 7 and 59 z ~ 8 candidate galaxies in the reionization epoch, and use this large 26-29.4?AB?mag sample of galaxies to derive very deep luminosity functions to < ? 18?AB?mag and the star formation rate (SFR) density at z ~ 7 and z ~ 8 (just 800?Myr and 650?Myr after recombination, respectively). The galaxy sample is derived using a sophisticated Lyman-break technique on the full two-year Wide Field Camera 3/infrared (WFC3/IR) and Advanced Camera for Surveys (ACS) data available over the HUDF09 (~29.4?AB?mag, 5?), two nearby HUDF09 fields (~29?AB?mag, 5?, 14?arcmin2), and the wider area Early Release Science (~27.5?AB?mag, 5?, ~40?arcmin2). The application of strict optical non-detection criteria ensures the contamination fraction is kept low (just ~7% in the HUDF). This very low value includes a full assessment of the contamination from lower redshift sources, photometric scatter, active galactic nuclei, spurious sources, low-mass stars, and transients (e.g., supernovae). From careful modeling of the selection volumes for each of our search fields, we derive luminosity functions for galaxies at z ~ 7 and z ~ 8 to < ? 18?AB?mag. The faint-end slopes ? at z ~ 7 and z ~ 8 are uncertain but very steep at ? = ?2.01 ? 0.21 and ? = ?1.91 ? 0.32, respectively. Such steep slopes contrast to the local ? ?1.4 and may even be steeper than that at z ~ 4 where ? = ?1.73 ? 0.05. With such steep slopes (? ?1.7) lower luminosity galaxies dominate the galaxy luminosity density during the epoch of reionization. The SFR densities derived from these new z ~ 7 and z ~ 8 luminosity functions are consistent with the trends found at later times (lower redshifts). We find reasonable consistency with the SFR densities implied from reported stellar mass densities being only ~40% higher at z < 7. This suggests that (1) the stellar mass densities inferred from the Spitzer Infrared Array Camera (IRAC) photometry are reasonably accurate and (2) that the initial mass function at very high redshift may not be very different from that at later times.

The Star Formation History of Mass-selected Galaxies in the COSMOS Field

Abstract: We explore the redshift evolution of the specific star formation rate (SSFR) for galaxies of different stellar mass by drawing on a deep 3.6 µm-selected sample of > 10 5 galaxies in the 2 deg 2 COSMOS field. The average star formation rate (SFR) for sub-sets of these galaxies is estimated with stacked 1.4 GHz radio continuum emission. We separately consider the total sample and a subset of galaxies that shows evidence for substantive recent star formation in the rest-frame optical spectral energy distributions. At redshifts 0.2 2, at least for high-mass (M� & 4 � 10 10 M� ) systems where our conclusions are most robust. Our data show that there is a tight correlation with power-law dependence, SSFR / M� � , between

The Effects of Snowlines on C/O in Planetary Atmospheres

Abstract: The C/O ratio is predicted to regulate the atmospheric chemistry in hot Jupiters Recent observations suggest that some exoplanets, eg, Wasp 12-b, have atmospheric C/O ratios substantially different from the solar value of 054 In this Letter, we present a mechanism that can produce such atmospheric deviations from the stellar C/O ratio In protoplanetary disks, different snowlines of oxygen- and carbon-rich ices, especially water and carbon monoxide, will result in systematic variations in the C/O ratio both in the gas and in the condensed phases In particular, between the H2O and CO snowlines most oxygen is present in icy grains—the building blocks of planetary cores in the core accretion model—while most carbon remains in the gas phase This region is coincidental with the giant-planet-forming zone for a range of observed protoplanetary disks Based on standard core accretion models of planet formation, gas giants that sweep up most of their atmospheres from disk gas outside of the water snowline will have a C/O ~ 1, while atmospheres significantly contaminated by evaporating planetesimals will have a stellar or substellar C/O when formed at the same disk radius The overall metallicity will also depend on the atmosphere formation mechanism, and exoplanetary atmospheric compositions may therefore provide constraints on where and how a specific planet formed

A method for measuring (slopes of) the mass profiles of dwarf spheroidal galaxies

Abstract: We introduce a method for measuring the slopes of mass profiles within dwarf spheroidal (dSph) galaxies directly from stellar spectroscopic data and without adopting a dark matter halo model. Our method combines two recent results: (1) spherically symmetric, equilibrium Jeans models imply that the product of half-light radius and (squared) stellar velocity dispersion provides an estimate of the mass enclosed within the half-light radius of a dSph stellar component, and (2) some dSphs have chemodynamically distinct stellar subcomponents that independently trace the same gravitational potential. We devise a statistical method that uses measurements of stellar positions, velocities, and spectral indices to distinguish two dSph stellar subcomponents and to estimate their individual half-light radii and velocity dispersions. For a dSph with two detected stellar subcomponents, we obtain estimates of masses enclosed at two discrete points in the same mass profile, immediately defining a slope. Applied to published spectroscopic data, our method distinguishes stellar subcomponents in the Fornax and Sculptor dSphs, for which we measure slopes Γ ≡ Δlog M/Δlog r = 2.61+0.43 –0.37 and Γ = 2.95+0.51 –0.39, respectively. These values are consistent with "cores" of constant density within the central few hundred parsecs of each galaxy and rule out "cuspy" Navarro-Frenk-White (NFW) profiles (dlog M/dlog r ≤ 2 at all radii) with a significance 96% and 99%, respectively. Tests with synthetic data indicate that our method tends systematically to overestimate the mass of the inner stellar subcomponent to a greater degree than that of the outer stellar subcomponent, and therefore to underestimate the slope Γ (implying that the stated NFW exclusion levels are conservative).

Kepler 's First Rocky Planet: Kepler-10b

Abstract: NASA's Kepler Mission uses transit photometry to determine the frequency of Earth-size planets in or near the habitable zone of Sun-like stars. The mission reached a milestone toward meeting that goal: the discovery of its first rocky planet, Kepler-10b. Two distinct sets of transit events were detected: (1) a 152 ± 4 ppm dimming lasting 1.811 ± 0.024 hr with ephemeris T [BJD] = 2454964.57375^(+0.00060)_(–0.00082) + N * 0.837495^(+0.000004)_(–0.000005) days and (2) a 376 ± 9 ppm dimming lasting 6.86 ± 0.07 hr with ephemeris T [BJD] = 2454971.6761^(+0.0020)_(–0.0023) + N * 45.29485^(+0.00065) _(–0.00076) days. Statistical tests on the photometric and pixel flux time series established the viability of the planet candidates triggering ground-based follow-up observations. Forty precision Doppler measurements were used to confirm that the short-period transit event is due to a planetary companion. The parent star is bright enough for asteroseismic analysis. Photometry was collected at 1 minute cadence for >4 months from which we detected 19 distinct pulsation frequencies. Modeling the frequencies resulted in precise knowledge of the fundamental stellar properties. Kepler-10 is a relatively old (11.9 ± 4.5 Gyr) but otherwise Sun-like main-sequence star with T_(eff) = 5627 ± 44 K, M_⋆ = 0.895 ± 0.060 M_⊙ , and R_⋆ = 1.056 ± 0.021 R_⊙. Physical models simultaneously fit to the transit light curves and the precision Doppler measurements yielded tight constraints on the properties of Kepler-10b that speak to its rocky composition: M_P = 4.56^9+1.17)_(–1.29) M_⊕, R_P = 1.416^(+0.033)_(–0.036) R_⊕, and ρ_P = 8.8^(+2.1)_(–2.9) g cm^(–3). Kepler-10b is the smallest transiting exoplanet discovered to date.

THE SINS SURVEY OF z ∼ 2 GALAXY KINEMATICS: PROPERTIES OF THE GIANT STAR-FORMING CLUMPS*

Abstract: We have studied the properties of giant star-forming clumps in five z ~ 2 star-forming disks with deep SINFONI AO spectroscopy at the ESO VLT. The clumps reside in disk regions where the Toomre Q-parameter is below unity, consistent with their being bound and having formed from gravitational instability. Broad Hα/[N II] line wings demonstrate that the clumps are launching sites of powerful outflows. The inferred outflow rates are comparable to or exceed the star formation rates, in one case by a factor of eight. Typical clumps may lose a fraction of their original gas by feedback in a few hundred million years, allowing them to migrate into the center. The most active clumps may lose much of their mass and disrupt in the disk. The clumps leave a modest imprint on the gas kinematics. Velocity gradients across the clumps are 10-40 km s–1 kpc–1, similar to the galactic rotation gradients. Given beam smearing and clump sizes, these gradients may be consistent with significant rotational support in typical clumps. Extreme clumps may not be rotationally supported; either they are not virialized or they are predominantly pressure supported. The velocity dispersion is spatially rather constant and increases only weakly with star formation surface density. The large velocity dispersions may be driven by the release of gravitational energy, either at the outer disk/accreting streams interface, and/or by the clump migration within the disk. Spatial variations in the inferred gas phase oxygen abundance are broadly consistent with inside-out growing disks, and/or with inward migration of the clumps.

MASSIVE MOLECULAR OUTFLOWS AND NEGATIVE FEEDBACK IN ULIRGs OBSERVED BY HERSCHEL-PACS*

Abstract: Mass outflows driven by stars and active galactic nuclei (AGNs) are a key element in many current models of galaxy evolution. They may produce the observed black-hole-galaxy mass relation and regulate and quench both star formation in the host galaxy and black hole accretion. However, observational evidence of such feedback processes through outflows of the bulk of the star-forming molecular gas is still scarce. Here we report the detection of massive molecular outflows, traced by the hydroxyl molecule (OH), in far-infrared spectra of ULIRGs obtained with Herschel-PACS as part of the SHINING key project. In some of these objects the (terminal) outflow velocities exceed 1000?km?s?1, and their outflow rates (up to ~1200 M ? yr?1) are several times larger than their star formation rates. We compare the outflow signatures in different types of ULIRGs and in starburst galaxies to address the issue of the energy source (AGN or starburst) of these outflows. We report preliminary evidence that ULIRGs with a higher AGN luminosity (and higher AGN contribution to L IR) have higher terminal velocities and shorter gas depletion timescales. The outflows in the observed ULIRGs are able to expel the cold gas reservoirs from the centers of these objects within ~106-108 years.

Forming realistic late-type spirals in a λcdm universe: the eris simulation

Abstract: Simulations of the formation of late-type spiral galaxies in a cold dark matter ({Lambda}CDM) universe have traditionally failed to yield realistic candidates. Here we report a new cosmological N-body/smooth particle hydrodynamic simulation of extreme dynamic range in which a close analog of a Milky Way disk galaxy arises naturally. Named 'Eris', the simulation follows the assembly of a galaxy halo of mass M{sub vir} = 7.9 Multiplication-Sign 10{sup 11} M{sub Sun} with a total of N = 18.6 million particles (gas + dark matter + stars) within the final virial radius, and a force resolution of 120 pc. It includes radiative cooling, heating from a cosmic UV field and supernova explosions (blastwave feedback), a star formation recipe based on a high gas density threshold (n{sub SF} = 5 atoms cm{sup -3} rather than the canonical n{sub SF} = 0.1 atoms cm{sup -3}), and neglects any feedback from an active galactic nucleus. Artificial images are generated to correctly compare simulations with observations. At the present epoch, the simulated galaxy has an extended rotationally supported disk with a radial scale length R{sub d} = 2.5 kpc, a gently falling rotation curve with circular velocity at 2.2 disk scale lengths of V{sub 2.2}more » = 214 km s{sup -1}, an i-band bulge-to-disk ratio B/D = 0.35, and a baryonic mass fraction within the virial radius that is 30% below the cosmic value. The disk is thin, has a typical H I-to-stellar mass ratio, is forming stars in the region of the {Sigma}{sub SFR}-{Sigma}{sub HI} plane occupied by spiral galaxies, and falls on the photometric Tully-Fisher and the stellar-mass-halo-virial-mass relations. Hot (T > 3 Multiplication-Sign 10{sup 5} K) X-ray luminous halo gas makes up only 26% of the universal baryon fraction and follows a 'flattened' density profile {proportional_to}r{sup -1.13} out to r = 100 kpc. Eris appears then to be the first cosmological hydrodynamic simulation in which the galaxy structural properties, the mass budget in the various components, and the scaling relations between mass and luminosity are all consistent with a host of observational constraints. A twin simulation with a low star formation density threshold results in a galaxy with a more massive bulge and a much steeper rotation curve, as in previously published work. A high star formation threshold appears therefore key in obtaining realistic late-type galaxies, as it enables the development of an inhomogeneous interstellar medium where star formation and heating by supernovae occur in a clustered fashion. The resulting outflows at high redshifts reduce the baryonic content of galaxies and preferentially remove low-angular-momentum gas, decreasing the mass of the bulge component. Simulations of even higher resolution that follow the assembly of galaxies with different merger histories shall be used to verify our results.« less

Black hole formation in failing core-collapse supernovae

Abstract: We present results of a systematic study of failing core-collapse supernovae and the formation of stellar-mass black holes (BHs). Using our open-source general-relativistic 1.5D code GR1D equipped with a three-species neutrino leakage/heating scheme and over 100 presupernova models, we study the effects of the choice of nuclear equation of state (EOS), zero-age main sequence (ZAMS) mass and metallicity, rotation, and mass-loss prescription on BH formation. We find that the outcome, for a given EOS, can be estimated, to first order, by a single parameter, the compactness of the stellar core at bounce. By comparing protoneutron star (PNS) structure at the onset of gravitational instability with solutions of the Tolman–Oppenheimer–Volkof equations, we find that thermal pressure support in the outer PNS core is responsible for raising the maximum PNS mass by up to 25% above the cold NS value. By artificially increasing neutrino heating, we find the critical neutrino heating efficiency required for exploding a given progenitor structure and connect these findings with ZAMS conditions, establishing, albeit approximately, for the first time based on actual collapse simulations, the mapping between ZAMS parameters and the outcome of core collapse. We also study the effect of progenitor rotation and find that the dimensionless spin of nascent BHs may be robustly limited below a* = Jc/GM^2 = 1 by the appearance of nonaxisymmetric rotational instabilities.

A measurement of the damping tail of the cosmic microwave background power spectrum with the south pole telescope

Abstract: We present a measurement of the angular power spectrum of the cosmic microwave background (CMB) using data from the South Pole Telescope (SPT). The data consist of 790 square degrees of sky observed at 150 GHz during 2008 and 2009. Here we present the power spectrum over the multipole range 650 < ‘ < 3000, where it is dominated by primary CMB anisotropy. We combine this power spectrum with the power spectra from the seven-year Wilkinson Microwave Anisotropy Probe (WMAP) data release to constrain cosmological models. We nd that the SPT and WMAP data are consistent with each other and, when combined, are well t by a spatially at, CDM cosmological model. The SPT+WMAP constraint on the spectral index of scalar uctuations is ns = 0:9663 0:0112. We detect, at 5 signicance, the eect of gravitational lensing on the CMB power spectrum, and nd its amplitude to be consistent with the CDM cosmological model. We explore a number of extensions beyond the CDM model. Each extension is tested independently, although there are degeneracies between some of the extension parameters. We constrain the tensorto-scalar ratio to be r < 0:21 (95% CL) and constrain the running of the scalar spectral index to be dns=d lnk = 0:024 0:013. We strongly detect the eects of primordial helium and neutrinos on the CMB; a model without helium is rejected at 7.7 , while a model without neutrinos is rejected at 7.5 . The primordial helium abundance is measured to be Yp = 0:296 0:030, and the eective number of relativistic species is measured to be Ne = 3:85 0:62. The constraints on these models are strengthened when the CMB data are combined with measurements of the Hubble constant and the baryon acoustic oscillation feature. Notable improvements include ns = 0:9668 0:0093, r < 0:17 (95% CL), and Ne = 3:86 0:42. The SPT+WMAP data show a mild preference for low power in the CMB damping tail, and while this preference may be accommodated by models that have a negative spectral running, a high primordial helium abundance, or a high eective number of relativistic species, such models are disfavored by the abundance of low-redshift galaxy clusters. Subject headings: cosmology { cosmology:cosmic microwave background { cosmology: observations { large-scale structure of universe

Dust-corrected star formation rates of galaxies. ii. combinations of ultraviolet and infrared tracers

Abstract: We present new calibrations of far-ultraviolet (FUV) attenuation as derived from the total infrared to FUV luminosity ratio (IRX) and the FUV-near-UV(NUV) color. We find that the IRX-corrected FUV luminosities are tightly and linearly correlated with the attenuation-corrected H{alpha} luminosities (as measured from the Balmer decrement), with an rms scatter of {+-}0.09 dex. The ratios of these attenuation-corrected FUV to H{alpha} luminosities are consistent with evolutionary synthesis model predictions, assuming a constant star formation rate over 100 Myr, solar metallicity, and either a Salpeter or a Kroupa initial mass function with lower and upper mass limits of 0.1 and 100 M{sub Sun }. The IRX-corrected FUV to Balmer-corrected H{alpha} luminosity ratios do not show any trend with other galactic properties over the ranges covered by our sample objects. In contrast, FUV attenuation derived from the FUV-NUV color (UV spectral slope) show much larger random and systematic uncertainties. When compared to either Balmer-corrected H{alpha} luminosities or IRX-corrected FUV luminosities the color-corrected FUV luminosities show {approx}2.5 times larger rms scatter, and systematic nonlinear deviations as functions of luminosity and other parameters. Linear combinations of 25 {mu}m and 1.4 GHz radio continuum luminosities with the observed FUV luminosities are also well correlated withmore » the Balmer-corrected H{alpha} luminosities. These results provide useful prescriptions for deriving attenuation-corrected star formation rates of galaxies based on linear combinations of UV and IR or radio luminosities, which are presented in convenient tabular form. Comparisons of our calibrations with attenuation corrections in the literature and with dust attenuation laws are also made.« less

The CO-to-H2 Conversion Factor from Infrared Dust Emission across the Local Group

Abstract: We estimate the conversion factor relating CO emission to H2 mass, αCO, in five Local Group galaxies that span approximately an order of magnitude in metallicity—M 31, M 33, the Large Magellanic Cloud (LMC), NGC 6822, and the Small Magellanic Cloud (SMC). We model the dust mass along the line of sight from infrared (IR) emission and then solve for the αCO that best allows a single gas-to-dust ratio (δGDR) to describe each system. This approach remains sensitive to CO-dark envelopes H2 surrounding molecular clouds. In M 31, M 33, and the LMC we find αCO 3-9 M ☉ pc–2 (K km s–1)–1, consistent with the Milky Way value within the uncertainties. The two lowest metallicity galaxies in our sample, NGC 6822 and the SMC (12 + log (O/H) 8.2 and 8.0), exhibit a much higher αCO. Our best estimates are αNGC6822 CO 30 M ☉ pc–2 (K km s–1)–1 and αSMC CO 70 M ☉ pc–2 (K km s–1)–1. These results are consistent with the conversion factor becoming a strong function of metallicity around 12 + log (O/H) ~ 8.4-8.2. We favor an interpretation where decreased dust shielding leads to the dominance of CO-free envelopes around molecular clouds below this metallicity.

The spitzer ice legacy: ice evolution from cores to protostars

Abstract: Ices regulate much of the chemistry during star formation and account for up to 80% of the available oxygen and carbon. In this paper, we use the Spitzer c2d Legacy ice survey, complimented with data sets on ices in cloud cores and high-mass protostars, to determine standard ice abundances and to present a coherent picture of the evolution of ices during low- and high-mass star formation. The median ice composition H_(2)O:CO:CO_2:CH_(3)OH:NH_3:CH_4:XCN is 100:29:29:3:5:5:0.3 and 100:13:13:4:5:2:0.6 toward low- and high-mass protostars, respectively, and 100:31:38:4:-:-:- in cloud cores. In the low-mass sample, the ice abundances with respect to H_(2)O of CH_4, NH_3, and the component of CO_2 mixed with H_(2)O typically vary by <25%, indicative of co-formation with H_(2)O. In contrast, some CO and CO_2 ice components, XCN, and CH3OH vary by factors 2-10 between the lower and upper quartile. The XCN band correlates with CO, consistent with its OCN– identification. The origin(s) of the different levels of ice abundance variations are constrained by comparing ice inventories toward different types of protostars and background stars, through ice mapping, analysis of cloud-to-cloud variations, and ice (anti-)correlations. Based on the analysis, the first ice formation phase is driven by hydrogenation of atoms, which results in an H_(2)O-dominated ice. At later prestellar times, CO freezes out and variations in CO freezeout levels and the subsequent CO-based chemistry can explain most of the observed ice abundance variations. The last important ice evolution stage is thermal and UV processing around protostars, resulting in CO desorption, ice segregation, and the formation of complex organic molecules. The distribution of cometary ice abundances is consistent with the idea that most cometary ices have a protostellar origin.

SNLS3: Constraints on dark energy combining the supernova legacy survey three-year data with other probes

Abstract: We present observational constraints on the nature of dark energy using the Supernova Legacy Survey three-year sample (SNLS3) of Guy et al. and Conley et al. We use the 472 Type Ia supernovae (SNe Ia) in this sample, accounting for recently discovered correlations between SN Ia luminosity and host galaxy properties, and include the effects of all identified systematic uncertainties directly in the cosmological fits. Combining the SNLS3 data with the full WMAP7 power spectrum, the Sloan Digital Sky Survey luminous red galaxy power spectrum, and a prior on the Hubble constant H_0 from SHOES, in a flat universe we find Ω_m = 0.269 ± 0.015 and w = –1.061^(+0.069)_(–0.068) (where the uncertainties include all statistical and SN Ia systematic errors)—a 6.5% measure of the dark energy equation-of-state parameter w. The statistical and systematic uncertainties are approximately equal, with the systematic uncertainties dominated by the photometric calibration of the SN Ia fluxes—without these calibration effects, systematics contribute only a ~2% error in w. When relaxing the assumption of flatness, we find Ω_m = 0.271 ± 0.015, Ω_k = –0.002 ± 0.006, and w = –1.069^(+0.091)_(–0.092). Parameterizing the time evolution of w as w(a) = w_0 + w_a (1–a) gives w_0 = –0.905 ± 0.196, w_a = –0.984^(+1.094)_(– 1.097) in a flat universe. All of our results are consistent with a flat, w = –1 universe. The size of the SNLS3 sample allows various tests to be performed with the SNe segregated according to their light curve and host galaxy properties. We find that the cosmological constraints derived from these different subsamples are consistent. There is evidence that the coefficient, β, relating SN Ia luminosity and color, varies with host parameters at >4σ significance (in addition to the known SN luminosity-host relation); however, this has only a small effect on the cosmological results and is currently a subdominant systematic.

The star formation rate of supersonic magnetohydrodynamic turbulence

Abstract: This work presents a new physical model of the star formation rate (SFR), which is verified with an unprecedented set of large numerical simulations of driven, supersonic, self-gravitating, magneto-hydrodynamic (MHD) turbulence, where collapsing cores are captured with accreting sink particles. The model depends on the relative importance of gravitational, turbulent, magnetic, and thermal energies, expressed through the virial parameter, αvir, the rms sonic Mach number, , and the ratio of mean gas pressure to mean magnetic pressure, β0. The SFR is predicted to decrease with increasing αvir (stronger turbulence relative to gravity), to increase with increasing (for constant values of αvir), and to depend weakly on β0 for values typical of star forming regions (-20 and β0 1-20). In the unrealistic limit of β0 → ∞, that is, in the complete absence of a magnetic field, the SFR increases approximately by a factor of three, which shows the importance of magnetic fields in the star formation process, even when they are relatively weak (super-Alfvenic turbulence). The star-formation simulations used to test the model result in an approximately constant SFR, after an initial transient phase. The dependence of the SFR on the virial parameter is shown to agree very well with the theoretical predictions.

Simulations on a moving mesh: the clustered formation of population iii protostars

Abstract: The cosmic dark ages ended a few hundred million years after the big bang, when the first stars began to fill the universe with new light. It has generally been argued that these stars formed in isolation and were extremely massive—perhaps 100 times as massive as the Sun. In a recent study, Clark and collaborators showed that this picture requires revision. They demonstrated that the accretion disks that build up around Population III stars are strongly susceptible to fragmentation and that the first stars should therefore form in clusters rather than in isolation. We here use a series of high-resolution hydrodynamical simulations performed with the moving mesh code AREPO to follow up on this proposal and to study the influence of environmental parameters on the level of fragmentation. We model the collapse of five independent minihalos from cosmological initial conditions, through the runaway condensation of their central gas clouds, to the formation of the first protostar, and beyond for a further 1000 years. During this latter accretion phase, we represent the optically thick regions of protostars by sink particles. Gas accumulates rapidly in the circumstellar disk around the first protostar, fragmenting vigorously to produce a small group of protostars. After an initial burst, gravitational instability recurs periodically, forming additional protostars with masses ranging from ~0.1 to 10 M ☉. Although the shape, multiplicity, and normalization of the protostellar mass function depend on the details of the sink-particle algorithm, fragmentation into protostars with diverse masses occurs in all cases, confirming earlier reports of Population III stars forming in clusters. Depending on the efficiency of later accretion and merging, Population III stars may enter the main sequence in clusters and with much more diverse masses than are commonly assumed.

THE NEWFIRM MEDIUM-BAND SURVEY: PHOTOMETRIC CATALOGS, REDSHIFTS, AND THE BIMODAL COLOR DISTRIBUTION OF GALAXIES OUT TO z ∼ 3

Abstract: We present deep near-IR (NIR) medium-bandwidth photometry over the wavelength range 1-1.8 μm in the All-wavelength Extended Groth strip International Survey (AEGIS) and Cosmic Evolution Survey (COSMOS) fields. The observations were carried out using the NOAO Extremely Wide-Field Infrared Imager (NEWFIRM) on the Mayall 4 m Telescope on Kitt Peak as part of the NEWFIRM Medium-Band Survey (NMBS), an NOAO survey program. In this paper, we describe the full details of the observations, data reduction, and photometry for the survey. We also present a public K-selected photometric catalog, along with accurate photometric redshifts. The redshifts are computed with 37 (20) filters in the COSMOS (AEGIS) fields, combining the NIR medium-bandwidth data with existing UV (Galaxy Evolution Explorer), visible and NIR (Canada-France-Hawaii Telescope and Subaru Telescope), and mid-IR (Spitzer/IRAC) imaging. We find excellent agreement with publicly available spectroscopic redshifts, with σ z /(1 + z) ~ 1%-2% for ~4000 galaxies at z = 0-3. The NMBS catalogs contain ~13,000 galaxies at z > 1.5 with accurate photometric redshifts and rest-frame colors. Due to the increased spectral resolution obtained with the five NIR medium-band filters, the median 68% confidence intervals of the photometric redshifts of both quiescent and star-forming galaxies are a factor of about two times smaller when comparing catalogs with medium-band NIR photometry to NIR broadband photometry. We show evidence for a clear bimodal color distribution between quiescent and star-forming galaxies that persists to z ~ 3, a higher redshift than has been probed so far.