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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 685 records · Page 38
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DOE OSTI2011

H I CONTENT AND OPTICAL PROPERTIES OF FIELD GALAXIES FROM THE ALFALFA SURVEY. II. MULTIVARIATE ANALYSIS OF A GALAXY SAMPLE IN LOW-DENSITY ENVIRONMENTS

This is the second paper of two reporting results from a study of the H I content and stellar properties of nearby galaxies detected by the Arecibo Legacy Fast ALFA blind 21 cm line survey and the Sloan Digital Sky Survey in a 2160 deg{sup 2} region of high galactic latitude sky covered by both surveys, in the general Virgo direction. Here, we analyze a complete H I flux-limited subset of 1624 objects with homogeneously measured 21 cm and multi-wavelength optical attributes extracted from the control sample of H I emitters in environments of low local galactic density assembled by Toribio et al. (Paper I). Strategies of multivariate data analysis are applied to this data set in order to (i) investigate the correlation structure of the space defined by an extensive set of potentially independent observables describing gas-rich systems, (ii) identify the intrinsic parameters that best define their neutral gas content, and (iii) explore the scaling relations arising from the joint distributions of the quantities most strongly correlated with the H I mass. The principal component analysis performed over a set of five galaxy properties reveals that they are strongly interrelated, supporting previous claims that nearby H I emitters show a high degree of correlation. The best predictors for the expected value of M{sub HI} are the diameter of the stellar disk, D{sub 25,r}, followed by the total luminosity (both in the r band), and the maximum rotation speed, while morphological proxies such as color show only a moderately strong correlation with the gaseous content attenuated by observational error. Among the various inferred prescriptions, the simplest and most accurate is log(M{sub HI}/M{sub sun}) = 8.72 + 1.25 log(D{sub 25,r}/kpc). We find a slope of -8.2 {+-} 0.5 for the relation between optical magnitude and log rotation speed, in good agreement with Tully-Fisher studies, as well as a log slope of 1.55 {+-} 0.06 for the H I mass-optical galaxy size relation. Given the homogeneity of the measurements and the completeness of our data set, the latter outcome suggests that the constancy of the average (hybrid) H I surface density advocated by some authors for the spiral population is just a crude approximation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

MULTIPHASE GAS IN GALAXY HALOS: THE O VI LYMAN-LIMIT SYSTEM TOWARD J1009+0713

We have serendipitously detected a strong O VI-bearing Lyman-limit system (LLS) at z{sub abs} = 0.3558 toward the quasi-stellar object (QSO) J1009+0713 (z{sub em} = 0.456) in our survey of low-redshift galaxy halos with the Hubble Space Telescope's (HST) Cosmic Origins Spectrograph. Its total rest-frame equivalent width of W{sub r} = 835 {+-} 49 mA and column density of log N(O VI) = 15.0 are the highest for an intervening absorber yet detected in any low-redshift QSO sightline, with absorption spanning at least four major kinematic component groups over 400 km s{sup -1} in its rest frame. HST/Wide Field Camera 3 images of the galaxy field show that the absorber is associated with two galaxies lying at 14 and 46 kpc from the QSO line of sight. The absorber is kinematically complex and there are no less than nine individual Mg II components spanning 200 km s{sup -1} in our Keck/HIRES optical data. The bulk of the absorbing gas traced by H I resides in two strong, blended component groups that possess a total log N(H I) {approx_equal} 18-18.8, but most of the O VI is associated with two outlying components with log N(H I) = 14.8 and 16.5. The ion ratios and column densities of C, N, O, Mg, Si, S, and Fe, except the O VI, can be accommodated into a simple photoionization model in which diffuse, low-metallicity halo gas is exposed to a photoionizing field from stars in the nearby galaxies that propagates into the halo at 10% efficiency. In this model, the clouds have neutral fractions of {approx}1%-10% and thus total hydrogen column densities of log N(H) {approx_equal} 19.5. Direct measurement of the gas metallicity is precluded by saturation of the main components of H I, but we constrain the metallicity firmly within the range 0.1-1 Z{sub sun}, and photoionization modeling indirectly indicates a subsolar metallicity of 0.05-0.5 Z{sub sun}. This highly ionized, multiphase, possibly low-metallicity halo gas resembles gas with similar properties in the Milky Way halo and other low-redshift LLS, suggesting that at least some other galaxies have their star formation fueled by metal-poor gas accreting from the intergalactic medium and ionized by the stars in the host galaxy. As observed in the Milky Way high-velocity clouds, the strong detected O VI is not consistent with the photoionization scenario but is consistent with general picture in which O VI arises in interface material surrounding the photoionized clouds or in a hotter, diffuse component of the halo. The appearance of strong O VI and nine Mg II components in this system, and our review of similar systems in the literature, offer some support to this 'interface' picture of high-velocity O VI: the total strength of the O VI shows a positive correlation with the number of detected components in the low-ionization gas.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

A HUBBLE SPACE TELESCOPE STUDY OF LYMAN LIMIT SYSTEMS: CENSUS AND EVOLUTION

We present a survey for optically thick Lyman limit absorbers at z < 2.6 using archival Hubble Space Telescope observations with the Faint Object Spectrograph and Space Telescope Imaging Spectrograph. We identify 206 Lyman limit systems (LLSs), increasing the number of cataloged LLSs at z < 2.6 by a factor of {approx}10. We compile a statistical sample of 50 {tau}{sub LLS} {>=} 2 LLSs drawn from 249 QSO sight lines that avoid known targeting biases. The incidence of such LLSs per unit redshift, l(z) = dn/dz, at these redshifts is well described by a single power law, l(z){proportional_to}(1 + z){sup {gamma}}, with {gamma} = 1.33 {+-} 0.61 at z < 2.6, or with {gamma} = 1.83 {+-} 0.21 over the redshift range 0.2 {<=} z {<=} 4.9. The incidence of LLSs per absorption distance, l(X), decreases by a factor of {approx}1.5 over the {approx}0.6 Gyr from z = 4.9 to 3.5; l(X) evolves much more slowly at low redshifts, decreasing by a similar factor over the {approx}8 Gyr from z = 2.6 to 0.25. We show that the column density distribution function, f(N{sub HI}), at low redshift is not well fitted by a single power-law index (f(N{sub HI}) {proportional_to} N{sup -}{beta}{sub HI}) over the column density range 13 {<=} log N{sub HI} {<=} 22 or log N{sub HI} {>=} 17.2. While low- and high-redshift f(N{sub HI}) distributions are consistent for log N{sub HI}>19.0, there is some evidence that f(N{sub HI}) evolves with z for log N{sub HI} {approx}< 17.7, possibly due to the evolution of the UV background and galactic feedback. Assuming LLSs are associated with individual galaxies, we show that the physical cross section of the optically thick envelopes of galaxies decreased by a factor of {approx}9 from z {approx} 5 to 2 and has remained relatively constant since that time. We argue that a significant fraction of the observed population of LLSs arises in the circumgalactic gas of sub-L{sub *} galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

BREAKING THE LAW: THE M{sub bh}-M{sub spheroid} RELATIONS FOR CORE-SERSIC AND SERSIC GALAXIES

The popular log-linear relation between supermassive black hole mass, M{sub bh}, and the dynamical mass of the host spheroid, M{sub sph}, is shown to require a significant correction. Core galaxies, typically with M{sub bh} {approx}> 2 Multiplication-Sign 10{sup 8} M{sub Sun} and thought to be formed in dry merger events, are shown to be well described by a linear relation for which the median black hole mass is 0.36%-roughly double the old value of constancy. Of greater significance is that M{sub bh}{proportional_to}M{sup 2}{sub sph} among the (non-pseudobulge) lower-mass systems: specifically, log [M{sub bh}/M{sub Sun }] = (1.92 {+-} 0.38)log [M{sub sph}/7 Multiplication-Sign 10{sup 10} M{sub Sun }] + (8.38 {+-} 0.17). 'Classical' spheroids hosting a 10{sup 6} M{sub Sun} black hole will have M{sub bh}/M{sub sph} {approx} 0.025%. These new relations presented herein (1) bring consistency to the relation M{sub bh}{proportional_to}{sigma}{sup 5} and the fact that L{proportional_to}{sigma}{sup x} with exponents of 5 and 2 for bright (M{sub B} {approx}< -20.5 mag) and faint spheroids, respectively, (2) mimic the non-(log-linear) behavior known to exist in the M{sub bh}-(Sersic n) diagram, (3) necessitate the existence of a previously overlooked M{sub bh}{proportional_to}L{sup 2.5} relation for Sersic (i.e., not core-Sersic) galaxies, and (4) resolve past conflicts (in mass prediction) with the M{sub bh}-{sigma} relation at the low-mass end. Furthermore, the bent nature of the M{sub bh}-M{sub sph} relation reported here for 'classical' spheroids will have a host of important implications that, while not addressed in this paper, relate to (1) galaxy/black hole formation theories, (2) searches for the fundamental, rather than secondary, black hole scaling relation, (3) black hole mass predictions in other galaxies, (4) alleged pseudobulge detections, (5) estimates of the black hole mass function and mass density based on luminosity functions, (6) predictions for space-based gravitational wave detections, (7) connections with nuclear star cluster scaling relations, (8) evolutionary studies over different cosmic epochs, (9) comparisons and calibrations matching inactive black hole masses with low-mass active galactic nucleus data, and more.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

THE HALO MASSES AND GALAXY ENVIRONMENTS OF HYPERLUMINOUS QSOs AT z {approx_equal} 2.7 IN THE KECK BARYONIC STRUCTURE SURVEY

We present an analysis of the galaxy distribution surrounding 15 of the most luminous ({approx}> 10{sup 14} L{sub Sun }; M{sub 1450} {approx_equal} -30) QSOs in the sky with z {approx_equal} 2.7. Our data are drawn from the Keck Baryonic Structure Survey, which has been optimized to examine the small-scale interplay between galaxies and the intergalactic medium during the peak of the galaxy formation era at z {approx} 2-3. In this work, we use the positions and spectroscopic redshifts of 1558 galaxies that lie within {approx}3' (4.2 h{sup -1} comoving Mpc; cMpc) of the hyperluminous QSO (HLQSO) sight line in 1 of 15 independent survey fields, together with new measurements of the HLQSO systemic redshifts. By combining the spatial and redshift distributions, we measure the galaxy-HLQSO cross-correlation function, the galaxy-galaxy autocorrelation function, and the characteristic scale of galaxy overdensities surrounding the sites of exceedingly rare, extremely rapid, black hole accretion. On average, the HLQSOs lie within significant galaxy overdensities, characterized by a velocity dispersion {sigma}{sub v} {approx_equal} 200 km s{sup -1} and a transverse angular scale of {approx}25'' ({approx}200 physical kpc). We argue that such scales are expected for small groups with log (M{sub h}/M{sub Sun }) {approx_equal} 13. The galaxy-HLQSO cross-correlation function has a best-fit correlation length r{sup GQ}{sub 0} = (7.3 {+-} 1.3) h{sup -1} cMpc, while the galaxy autocorrelation measured from the spectroscopic galaxy sample in the same fields has r{sup GG}{sub 0} = (6.0 {+-} 0.5) h{sup -1} cMpc. Based on a comparison with simulations evaluated at z {approx} 2.6, these values imply that a typical galaxy lives in a host halo with log (M{sub h}/M{sub Sun }) = 11.9 {+-} 0.1, while HLQSOs inhabit host halos of log (M{sub h}/M{sub Sun }) = 12.3 {+-} 0.5. In spite of the extremely large black hole masses implied by their observed luminosities [log (M{sub BH}/M{sub Sun }) {approx}> 9.7], it appears that HLQSOs do not require environments very different from their much less luminous QSO counterparts. Evidently, the exceedingly low space density of HLQSOs ({approx}< 10{sup -9} cMpc{sup -3}) results from a one-in-a-million event on scales <<1 Mpc, and not from being hosted by rare dark matter halos.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

FLUX AND PHOTON SPECTRAL INDEX DISTRIBUTIONS OF FERMI-LAT BLAZARS AND CONTRIBUTION TO THE EXTRAGALACTIC GAMMA-RAY BACKGROUND

We present a determination of the distributions of the photon spectral index and gamma-ray flux-the so-called log N-log S relation-for the 352 blazars detected with a greater than approximately 7{sigma} detection threshold and located above {+-}20 Degree-Sign Galactic latitude by the Large Area Telescope of the Fermi Gamma-ray Space Telescope in its first year catalog. Because the flux detection threshold depends on the photon index, the observed raw distributions do not provide the true log N-log S counts or the true distribution of the photon index. We use the non-parametric methods developed by Efron and Petrosian to reconstruct the intrinsic distributions from the observed ones which account for the data truncations introduced by observational bias and includes the effects of the possible correlation between the two variables. We demonstrate the robustness of our procedures using a simulated data set of blazars and then apply these to the real data and find that for the population as a whole the intrinsic flux distribution can be represented by a broken power law with high and low indices of -2.37 {+-} 0.13 and -1.70 {+-} 0.26, respectively, and the intrinsic photon index distribution can be represented by a Gaussian with mean of 2.41 {+-} 0.13 and width of 0.25 {+-} 0.03. We also find the intrinsic distributions for the sub-populations of BL Lac and flat spectrum radio quasar type blazars separately. We then calculate the contribution of Fermi blazars to the diffuse extragalactic gamma-ray background radiation. Under the assumption that the flux distribution of blazars continues to arbitrarily low fluxes, we calculate the best-fit contribution of all blazars to the total extragalactic gamma-ray output to be 60%, with a large uncertainty.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

GeV Observations of star-forming glaxies with the FERMI Large Area Telescope

Recent detections of the starburst galaxies M82 and NGC 253 by gamma-ray telescopes suggest that galaxies rapidly forming massive stars are more luminous at gamma-ray energies compared to their quiescent relatives. Building upon those results, we examine a sample of 69 dwarf, spiral, and luminous and ultraluminous infrared galaxies at photon energies 0.1-100 GeV using 3 years of data collected by the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (Fermi). Measured fluxes from significantly detected sources and flux upper limits for the remaining galaxies are used to explore the physics of cosmic rays in galaxies. We find further evidence for quasi-linear scaling relations between gamma-ray luminosity and both radio continuum luminosity and total infrared luminosity which apply both to quiescent galaxies of the Local Group and low-redshift starburst galaxies (conservative P-values lesssim 0.05 accounting for statistical and systematic uncertainties). The normalizations of these scaling relations correspond to luminosity ratios of log (L 0.1-100 GeV/L 1.4 GHz) = 1.7 ± 0.1(statistical) ± 0.2(dispersion) and log (L 0.1-100 GeV/L 8-1000 μm) = –4.3 ± 0.1(statistical) ± 0.2(dispersion) for a galaxy with a star formation rate of 1 M ⊙ yr–1, assuming a Chabrier initial mass function. Using the relationship between infrared luminosity and gamma-ray luminosity, the collective intensity of unresolved star-forming galaxies at redshifts 0 < z < 2.5 above 0.1 GeV is estimated to be 0.4-2.4 × 10–6 ph cm–2 s–1 sr–1 (4%-23% of the intensity of the isotropic diffuse component measured with the LAT). We anticipate that ~10 galaxies could be detected by their cosmic-ray-induced gamma-ray emission during a 10 year Fermi mission.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

THE X-RAY STAR FORMATION STORY AS TOLD BY LYMAN BREAK GALAXIES IN THE 4 Ms CDF-S

We present results from deep X-ray stacking of >4000 high-redshift galaxies from z Almost-Equal-To 1 to 8 using the 4 Ms Chandra Deep Field-South data, the deepest X-ray survey of the extragalactic sky to date. The galaxy samples were selected using the Lyman break technique based primarily on recent Hubble Space Telescope ACS and WFC3 observations. Based on such high specific star formation rates (sSFRs): log SFR/M {sub *} > -8.7, we expect that the observed properties of these Lyman break galaxies (LBGs) are dominated by young stellar populations. The X-ray emission in LBGs, eliminating individually detected X-ray sources (potential active galactic nucleus), is expected to be powered by X-ray binaries and hot gas. We find, for the first time, evidence of evolution in the X-ray/SFR relation. Based on X-ray stacking analyses for z < 4 LBGs (covering {approx}90% of the universe's history), we find that the 2-10 keV X-ray luminosity evolves weakly with redshift (z) and SFR as log L {sub X} = 0.93log (1 + z) + 0.65log SFR + 39.80. By comparing our observations with sophisticated X-ray binary population synthesis models, we interpret that the redshift evolution of L {sub X}/SFR is driven by metallicity evolution in high mass X-ray binaries, likely the dominant population in these high sSFR galaxies. We also compare these models with our observations of X-ray luminosity density (total 2-10 keV luminosity per Mpc{sup 3}) and find excellent agreement. While there are no significant stacked detections at z {approx}> 5, we use our upper limits from 5 {approx}< z {approx}< 8 LBGs to constrain the supermassive black hole accretion history of the universe around the epoch of reionization.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

X-RAY PROPERTIES OF THE NORTHERN GALACTIC CAP SOURCES IN THE 58 MONTH SWIFT/BAT CATALOG

We present a detailed X-ray spectral analysis of the non-beamed, hard X-ray selected active galactic nuclei (AGNs) in the northern Galactic cap of the 58 month Swift Burst Alert Telescope (Swift/BAT) catalog, consisting of 100 AGNs with b > 50 Degree-Sign . This sky area has excellent potential for further dedicated study due to a wide range of multi-wavelength data that are already available, and we propose it as a low-redshift analog to the 'deep field' observations of AGNs at higher redshifts (e.g., CDFN/S, COSMOS, Lockman Hole). We present distributions of luminosity, absorbing column density, and other key quantities for the catalog. We use a consistent approach to fit new and archival X-ray data gathered from XMM-Newton, Swift/XRT, ASCA, and Swift/BAT. We probe to deeper redshifts than the 9 month BAT catalog ((z) = 0.043 compared to (z) = 0.03 for the 9 month catalog), and uncover a broader absorbing column density distribution. The fraction of obscured (log N {sub H} {>=} 22) objects in the sample is {approx}60%, and 43%-56% of the sample exhibits 'complex' 0.4-10 keV spectra. We present the properties of iron lines, soft excesses, and ionized absorbers for the subset of objects with sufficient signal-to-noise ratio. We reinforce previous determinations of the X-ray Baldwin (Iwasawa-Taniguchi) effect for iron K{alpha} lines. We also identify two distinct populations of sources; one in which a soft excess is well-detected and another where the soft excess is undetected, suggesting that the process responsible for producing the soft excess is not at work in all AGNs. The fraction of Compton-thick sources (log N {sub H} > 24.15) in our sample is {approx}9%. We find that 'hidden/buried AGNs' (which may have a geometrically thick torus or emaciated scattering regions) constitute {approx}14% of our sample, including seven objects previously not identified as hidden. Compton reflection is found to be important in a large fraction of our sample using joint XMM-Newton+BAT fits ((R) = 2.7 {+-} 0.75), indicating light bending or extremely complex absorption. High-energy cutoffs generally lie outside the BAT band (E > 200 keV) but are seen in some sources. We present the average 1-10 keV spectrum for the sample, which reproduces the 1-10 keV X-ray background slope as found for the brighter 9 month BAT AGN sample. The 2-10 keV log(N)-log(S) plot implies completeness down to fluxes a factor of {approx}4 fainter than seen in the 9 month catalog. We emphasize the utility of this northern Galactic cap sample for a wide variety of future studies on AGNs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

THE STRUCTURE OF THE X-RAY AND OPTICAL EMITTING REGIONS OF THE LENSED QUASAR Q 2237+0305

We use gravitational microlensing to determine the size of the X-ray and optical emission regions of the quadruple lens system Q 2237+0305. The optical half-light radius, log(R{sub 1/2,V}/cm) = 16.41 {+-} 0.18 (at {lambda}{sub rest} = 2018 A), is significantly larger than the observed soft, log(R{sub 1/2,soft}/cm)=15.76{sup +0.41}{sub -0.34} (1.1-3.5 keV in the rest frame), and hard, log(R{sub 1/2,hard}/cm)=15.46{sup +0.34}{sub -0.29} (3.5-21.5 keV in the rest frame), band X-ray emission. There is weak evidence that the hard component is more compact than the soft, with log(R{sub 1/2,soft}/R{sub 1/2,hard}){approx_equal}0.30{sup +0.53}{sub -0.45}. This wavelength-dependent structure agrees with recent results found in other lens systems using microlensing techniques, and favors geometries in which the corona is concentrated near the inner edge of the accretion disk. While the available measurements are limited, the size of the X-ray emission region appears to be roughly proportional to the mass of the central black hole.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

NEW RADIAL ABUNDANCE GRADIENTS FOR NGC 628 AND NGC 2403

Motivated by recent interstellar medium studies, we present high quality MMT and Gemini spectroscopic observations of H II regions in the nearby spiral galaxies NGC 628 and NGC 2403 in order to measure their chemical abundance gradients. Using long-slit and multi-object mask optical spectroscopy, we obtained measurements of the temperature sensitive auroral lines [O III] λ4363 and/or [N II] λ5755 at a strength of 4σ or greater in 11 H II regions in NGC 628 and 7 regions in NGC 2403. These observations allow us, for the first time, to derive an oxygen abundance gradient in NGC 628 based solely on 'direct' oxygen abundances of H II regions: 12 + log(O/H) = (8.43 ± 0.03) + (–0.017 ± 0.002) × R{sub g} (dex kpc{sup –1}), with a dispersion in log(O/H) of σ = 0.10 dex, from 14 regions with a radial coverage of ∼2-19 kpc. This is a significantly shallower slope than found by previous 'strong-line' abundance studies. In NGC 2403, we derive an oxygen abundance gradient of 12 + log(O/H) = (8.48 ± 0.04) + (–0.032 ± 0.007)× R{sub g} (dex kpc{sup –1}), with a dispersion in log(O/H) of σ = 0.07 dex, from seven H II with a radial coverage of ∼1-10 kpc. Additionally, we measure the N, S, Ne, and Ar abundances. We find the N/O ratio decreases with increasing radius for the inner disk, but reaches a plateau past R{sub 25} in NGC 628. NGC 2403 also has a negative N/O gradient with radius, but we do not sample the outer disk of the galaxy past R{sub 25} and so do not see evidence for a plateau. This bi-modal pattern measured for NGC 628 indicates dominant contributions from secondary nitrogen inside of the R{sub 25} transition and dominantly primary nitrogen farther out. As expected for α-process elements, S/O, Ne/O, and Ar/O are consistent with constant values over a range in oxygen abundance.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

K{sub s} -BAND LUMINOSITY EVOLUTION OF THE ASYMPTOTIC GIANT BRANCH POPULATION BASED ON STAR CLUSTERS IN THE LARGE MAGELLANIC CLOUD

We present a study of K{sub s} -band luminosity evolution of the asymptotic giant branch (AGB) population in simple stellar systems using star clusters in the Large Magellanic Cloud (LMC). We determine physical parameters of LMC star clusters including center coordinates, radii, and foreground reddenings. Ages of 83 star clusters are derived from isochrone fitting with the Padova models, and those of 19 star clusters are taken from the literature. The AGB stars in 102 star clusters with log(age) = 7.3-9.5 are selected using near-infrared color-magnitude diagrams based on Two Micron All Sky Survey photometry. Then we obtain the K{sub s} -band luminosity fraction of AGB stars in these star clusters as a function of ages. The K{sub s} -band luminosity fraction of AGB stars increases, on average, as age increases from log(age) ∼ 8.0, reaching a maximum at log(age) ∼ 8.5, and it decreases thereafter. There is a large scatter in the AGB luminosity fraction for given ages, which is mainly due to stochastic effects. We discuss this result in comparison with five simple stellar population models. The maximum K{sub s} -band AGB luminosity fraction for bright clusters is reproduced by the models that expect the value of 0.7-0.8 at log(age) = 8.5-8.7. We discuss the implication of our results with regard to the study of size and mass evolution of galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Choirs H I galaxy groups: The metallicity of dwarf galaxies

We present a recalibration of the luminosity-metallicity relation for gas-rich, star-forming dwarfs to magnitudes as faint as M{sub R} ∼ –13. We use the Dopita et al. metallicity calibrations to calibrate the relation for all the data in this analysis. In metallicity-luminosity space, we find two subpopulations within a sample of high-confidence Sloan Digital Sky Survey (SDSS) DR8 star-forming galaxies: 52% are metal-rich giants and 48% are metal-medium galaxies. Metal-rich dwarfs classified as tidal dwarf galaxy (TDG) candidates in the literature are typically of metallicity 12 + log(O/H) = 8.70 ± 0.05, while SDSS dwarfs fainter than M{sub R} = –16 have a mean metallicity of 12 + log(O/H) = 8.28 ± 0.10, regardless of their luminosity, indicating that there is an approximate floor to the metallicity of low-luminosity galaxies. Our hydrodynamical simulations predict that TDGs should have metallicities elevated above the normal luminosity-metallicity relation. Metallicity can therefore be a useful diagnostic for identifying TDG candidate populations in the absence of tidal tails. At magnitudes brighter than M{sub R} ∼ –16, our sample of 53 star-forming galaxies in 9 H I gas-rich groups is consistent with the normal relation defined by the SDSS sample. At fainter magnitudes, there is an increase in dispersion of the metallicity of our sample, suggestive of a wide range of H I content and environment. In our sample, we identify three (16% of dwarfs) strong TDG candidates (12 + log(O/H) > 8.6) and four (21%) very metal-poor dwarfs (12 + log(O/H) < 8.0), which are likely gas-rich dwarfs with recently ignited star formation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Probing the large and massive circumgalactic medium of a galaxy at z ∼ 0.2 using a pair of quasars

We present an analysis of two O VI absorbers at redshift z {sub abs} = 0.227, which were detected in the spectra of two closely spaced QSO sightlines (Q 0107–025A and B) and observed with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope. At the same redshift, the presence of a single bright (∼1.2L {sub *}) galaxy at an impact parameter of ∼200 kpc (proper) from both the sightlines was reported by Crighton et al. Using detailed photoionization models, we show that the high ionization phases of both the O VI absorbers have similar ionization conditions (e.g., log U ∼ –1.1 to –0.9), chemical enrichment (e.g., log Z ∼ –1.4 to –1.0), total hydrogen column density (e.g., log N {sub H}(cm{sup –2}) ∼ 19.6 – 19.7), and line of sight thickness (e.g., l {sub los} ∼ 600-800 kpc). Therefore we speculate that the O VI absorbers are tracing different parts of same large-scale structure, presumably the circumgalactic medium (CGM) of the identified galaxy. Using sizes along and transverse to the line of sight, we estimate the size of the CGM to be R ∼ 330 kpc. The baryonic mass associated with this large CGM as traced by O VI absorption is ∼1.2 × 10{sup 11} M {sub ☉}. A low ionization phase is detected in one of the O VI systems with near-solar metallicity (log Z = 0.20 ± 0.20) and parsec scale size (l {sub los} ∼ 6 pc), possibly tracing the neutral phase of a high-velocity cloud embedded within the CGM.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Curvature of the spectral energy distributions of blazars

In this paper, spectral energy distributions (SED) of both synchrotron and inverse Compton (IC) components of a sample of Fermi bright blazars are fitted by a log-parabolic law. The second-degree term of the log parabola measures the curvature of an SED. We find a statistically significant correlation between the synchrotron peak frequency and its curvature. This result is in agreement with the theoretical prediction and confirms previous studies that dealt with a single source with observations at various epochs or a small sample. If a broken power law is employed to fit the SED, the difference between the two spectral indices (i.e., |α{sub 2} – α{sub 1}|) can be considered a 'surrogate' of the SED curvature. We collect data from the literature and find a correlation between the synchrotron peak frequency and the spectral difference. We do not find a significant correlation between the IC peak frequency and its curvature, which may be caused by a complicated seed photon field. It is also found that the synchrotron curvatures are on average larger than those of IC curvatures, and there is no correlation between these two parameters. As suggested by previous works, both the log-parabolic law of the SED and the above correlation can be explained by statistical and/or stochastic particle accelerations. Based on a comparison of the slops of the correlation, our result seems to favor stochastic acceleration mechanisms and emission processes. Additional evidence, including SED modeling, particle acceleration simulation, and comparisons between some predictions and empirical relations/correlations, also seems to support the idea that the electron energy distribution (and/or synchrotron SED) may be log-parabolic.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Star formation rates from [C II] 158 μm and mid-infrared emission lines for starbursts and active galactic nuclei

A summary is presented for 130 galaxies observed with the Herschel Photodetector Array Camera and Spectrometer instrument to measure fluxes for the [C II] 158 μm emission line. Sources cover a wide range of active galactic nucleus to starburst classifications, as derived from polycyclic aromatic hydrocarbon strength measured with the Spitzer Infrared Spectrograph. Redshifts from [C II] and line to continuum strengths (equivalent width (EW) of [C II]) are given for the full sample, which includes 18 new [C II] flux measures. Calibration of L([C II)]) as a star formation rate (SFR) indicator is determined by comparing [C II] luminosities with mid-infrared [Ne II] and [Ne III] emission line luminosities; this gives the same result as determining SFR using bolometric luminosities of reradiating dust from starbursts: log SFR = log L([C II)]) – 7.0, for SFR in M{sub ☉} yr{sup –1} and L([C II]) in L{sub ☉}. We conclude that L([C II]) can be used to measure SFR in any source to a precision of ∼50%, even if total source luminosities are dominated by an active galactic nucleus (AGN) component. The line to continuum ratio at 158 μm, EW([C II]), is not significantly greater for starbursts (median EW([C II]) = 1.0 μm) compared to composites and AGNs (median EW([C II]) = 0.7 μm), showing that the far-infrared continuum at 158 μm scales with [C II] regardless of classification. This indicates that the continuum at 158 μm also arises primarily from the starburst component within any source, giving log SFR = log νL{sub ν}(158 μm) – 42.8 for SFR in M{sub ☉} yr{sup –1} and νL{sub ν}(158 μm) in erg s{sup –1}.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Systematic non-LTE study of the −2.6 ≤ [Fe/H] ≤ 0.2 F and G dwarfs in the solar neighborhood. I. Stellar atmosphere parameters

We present atmospheric parameters for 51 nearby F and G dwarf and subgiant stars uniformly distributed over the −2.60<[Fe/H]<+0.20 metallicity range that is suitable for the Galactic chemical evolution research. Lines of iron in the two ionization stages, Fe i and Fe ii, were used to derive a homogeneous set of effective temperatures, surface gravities, iron abundances, and microturbulence velocities. Our spectroscopic analyses took advantage of employing high-resolution (R ≥ 60,000) Shane/Hamilton and Canada–France–Hawaii Telescope/ESPaDOnS observed spectra and non-LTE (NLTE) line formation for Fe i and Fe ii in the classical one-dimensional model atmospheres. The spectroscopic method was tested in advance with the 20 benchmark stars, for which there are multiple measurements of the infrared flux method effective temperature and their Hipparcos parallax error is less than 10%. We found NLTE abundances from lines of Fe i and Fe ii to be consistent within 0.06 dex for every benchmark star, when applying a scaling factor of S{sub H} = 0.5 to the Drawinian rates of inelastic Fe+H collisions. The obtained atmospheric parameters were checked for each program star by comparing its position in the log g–T{sub eff} plane with the theoretical evolutionary track of given metallicity and α-enhancement in the Yi et al. grid. Our final effective temperatures lie exactly in between the T{sub IRFM} scales of Alonso et al. and Casagrande et al., with a mean difference of +46 and −51 K, respectively. NLTE leads to higher surface gravity compared with that for LTE. The shift in log g is smaller than 0.1 dex for stars with [Fe/H] ⩾−0.75, T{sub eff} ≤ 5750 K, or log g ≥ 4.20. NLTE analysis is crucial for the very metal-poor turnoff and subgiant stars, for which the shift in log g between NLTE and LTE can be up to 0.5 dex. The obtained accurate atmospheric parameters will be used in the forthcoming papers to determine NLTE abundances of important astrophysical elements from lithium to europium and to improve observational constraints on the chemodynamical models of the Galaxy evolution.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Radio jet feedback and star formation in heavily obscured, hyperluminous quasars at redshifts ∼ 0.5–3. I. ALMA observations

We present Atacama Large Millimeter/submillimeter Array (ALMA) 870 μm (345 GHz) data for 49 high-redshift (0.47 < z < 2.85), luminous (11.7<log(L{sub bol}/L{sub ⊙})<14.2) radio-powerful active galactic nuclei (AGNs), obtained to constrain cool dust emission from starbursts concurrent with highly obscured radiative-mode black hole (BH) accretion in massive galaxies that possess a small radio jet. The sample was selected from the Wide-field Infrared Survey Explorer with extremely steep (red) mid-infrared colors and with compact radio emission from NVSS/FIRST. Twenty-six sources are detected at 870 μm, and we find that the sample has large mid- to far-infrared luminosity ratios, consistent with a dominant and highly obscured quasar. The rest-frame 3 GHz radio powers are 24.7<log(P{sub 3.0 GHz}/W Hz{sup −1})<27.3, and all sources are radio-intermediate or radio-loud. BH mass estimates are 7.7 < log(M{sub BH}/M{sub ⊙}) < 10.2. The rest-frame 1–5 μm spectral energy distributions are very similar to the “Hot DOGs” (hot dust-obscured galaxies), and steeper (redder) than almost any other known extragalactic sources. ISM masses estimated for the ALMA-detected sources are 9.9 < log (M{sub ISM}/M{sub ⊙}) < 11.75 assuming a dust temperature of 30 K. The cool dust emission is consistent with star formation rates reaching several thousand M{sub ⊙} yr{sup −1}, depending on the assumed dust temperature, but we cannot rule out the alternative that the AGN powers all the emission in some cases. Our best constrained source has radiative transfer solutions with approximately equal contributions from an obscured AGN and a young (10–15 Myr) compact starburst.

79 ASTRONOMY AND ASTROPHYSICS↗