We present Hubble Space Telescope far-UV spectra of four QSOs whose sightlines pass through the halo of NGC 1097 at impact parameters of rho = 48-165 kpc. NGC 1097 is a nearby spiral galaxy that has ...undergone at least two minor merger events, but no apparent major mergers, and is relatively isolated with respect to other nearby bright galaxies. This makes NGC 1097 a good case study for exploring baryons in a paradigmatic bright-galaxy halo. Lyalpha absorption is detected along all sightlines and Si III lambda1206 is found along the three sightlines with the smallest rho; metal lines of C II, Si II, and Si IV are only found with certainty toward the innermost sightline. The kinematics of the absorption lines are best replicated by a model with a disk-like distribution of gas approximately planar to the observed 21 cm H i disk, which is rotating more slowly than the inner disk, and into which gas is infalling from the intergalactic medium. Some part of the absorption toward the innermost sightline may arise either from a small-scale outflow or from tidal debris associated with the minor merger that gives rise to the well known "dog-leg" stellar stream that projects from NGC 1097. When compared to other studies, NGC 1097 appears to be a "typical" absorber, although the large dispersion in absorption line column density and equivalent width in a single halo goes perhaps some way toward explaining the wide range of these values seen in higher-z studies.
We present an analysis of the mid-infrared (MIR) and optical properties of type 1 (broad-line) quasars detected by the Spitzer Space Telescope. The MIR color-redshift relation is characterized to z ...63, with predictions to z = 7. We demonstrate how combining MIR and optical colors can yield even more efficient selection of active galactic nuclei (AGNs)than MIR or optical colors alone. Composite spectral energy distributions (SEDs) are constructed for 259 quasars with both Sloan Digital Sky Survey and Spitzer photometry, supplemented by near-IR, GALEX, VLA, and ROSAT data, where available. We discuss how the spectral diversity of quasars influences the determination of bolometric luminosities and accretion rates; assuming the mean SED can lead to errors as large as 50% for individual quasars when inferring a bolometric luminosity from an optical luminosity. Finally, we show that careful consideration of the shape of the mean quasar SED and its redshift dependence leads to a lower estimate of the fraction of reddened/obscured AGNs missed by optical surveys as compared to estimates derived from a single mean MIR to optical flux ratio.
THE CASE FOR THE DUAL HALO OF THE MILKY WAY BEERS, Timothy C; CAROLLO, Daniela; SIVARANI, Thirupathi ...
The Astrophysical journal,
02/2012, Letnik:
746, Številka:
1
Journal Article
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Carollo et al. have recently resolved the stellar population of the Milky Way halo into at least two distinct components, an inner halo and an outer halo. This result has been criticized by Schonrich ...et al., who claim that the retrograde signature associated with the outer halo is due to the adoption of faulty distances. We refute this claim, and demonstrate that the Schonrich et al. photometric distances are themselves flawed because they adopted an incorrect main-sequence absolute magnitude relationship from the work of Ivezic et al. When compared to the recommended relation from Ivezic et al., which is tied to a Milky Way globular cluster distance scale and accounts for age and metallicity effects, the relation adopted by Schonrich et al. yields up to 18% shorter distances for stars near the main-sequence turnoff (TO). Use of the correct relationship yields agreement between the distances assigned by Carollo et al. and Ivezic et al. for low-metallicity dwarfs to within 6%-10%. Schonrich et al. also point out that intermediate-gravity stars (3.5 < or =, slant log g < 4.0) with colors redder than the TO region are likely misclassified, with which we concur. We implement a new procedure to reassign luminosity classifications for the TO stars that require it. New derivations of the rotational behavior demonstrate that the retrograde signature and high velocity dispersion of the outer-halo population remain. We summarize additional lines of evidence for a dual halo, including a test of the retrograde signature based on proper motions alone, and conclude that the preponderance of evidence strongly rejects the single-halo interpretation.
Abstract
We present MUSE observations of the field of the quasar Q0152−020, whose spectrum shows a Lyman limit system (LLS) at redshift zabs = 0.38, with a metallicity Z ≳ 0.06 Z⊙. The low-ionization ...metal lines associated with the LLS present two narrow distinct absorption components with a velocity separation of 26 km s−1. We detect six galaxies within 600 km s−1 from the absorption redshift; their projected distances from the quasar sightline range from 60 to 200 kpc. The optical spectra of five of these galaxies exhibit prominent nebular emission lines, from which we deduce extinction-corrected star formation rates in the range SFR = 0.06–1.3 M⊙ yr−1, and metallicities between 0.2 Z⊙ and Z⊙. The sixth galaxy is only detected in the stellar continuum. By combining our data with archival Keck/HIRES spectroscopy of the quasar and Hubble Space Telescope/Wide Field Planetary Camera 2 imaging of the field, we can relate absorption line and galaxy kinematics; we conclude that the LLS is most likely associated with the galaxy closest to the quasar sightline (galaxy ‘a’). Our morphokinematic analysis of galaxy ‘a’ combined with the absorption line kinematics supports the interpretation that one of the absorption components originates from an extension of the stellar disk of galaxy ‘a’, while the other component may arise in accreting gas in a warped disk with specific angular momentum ∼3 times larger than the specific angular momentum of the galaxy halo. Such warped disks are common features in hydrodynamical simulations of cold-flow accretion on to galaxies; the data presented here provide observational evidence in favour of this scenario.
We report the discovery of 13 confirmed two-image quasar lenses from a systematic search for gravitationally lensed quasars in the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS). We adopted ...a methodology similar to that used in the SDSS Quasar Lens Search (SQLS). In addition to the confirmed lenses, we report 11 quasar pairs with small angular separations ( ≲ 2 arcsec) confirmed from our spectroscopy, which are either projected pairs, physical binaries, or possibly quasar lens systems whose lens galaxies have not yet been detected. The newly discovered quasar lens system, SDSS J1452+4224 at z
s ≈ 4.8 is one of the highest redshift multiply imaged quasars found to date. Furthermore, we have over 50 good lens candidates yet to be followed up. Owing to the heterogeneous selection of BOSS quasars, the lens sample presented here does not have a well-defined selection function.
We exploit stellar population models of absorption line indices in the ultraviolet (from 2000 to 3200 ...) to study the spectra of massive galaxies. Our central aim is to investigate the occurrence ...at high redshift of the UV upturn, i.e. the increased UV emission due to old stars observed in massive galaxies and spiral bulges in the local Universe. We use a large (~275 000) sample of z ~ 0.6 massive (M*/M... > 11.5) galaxies using both individual spectra and stacks and employ a suite of models including a UV contribution from old populations, spanning various effective temperatures, fuel consumptions and metallicities. We find that a subset of our indices; Mg I, Fe I, and BL3096, are able to differentiate between old and young UV ages. We find evidence for old stars contributing to the UV in massive galaxies, rather than star formation. The data favour models with low/medium upturn temperatures (10 000-25 000 K) consistent with local galaxies, depending on the assumed metallicity, and with a larger fuel (f ~ 6.5 x 10 super( -2) M...). Models with one typical temperature are favoured over models with a temperature range, which would be typical of an extended horizontal branch. Old UV-bright populations are found in the whole galaxy sample (92 per cent), with a mass fraction peaking around 20-30 per cent. Upturn galaxies are massive and have redder colours, in agreement with findings in the local Universe. We find that the upturn phenomenon appears at z ~ 1 and its frequency increases towards lower redshift, as expected by stellar evolution of low-mass stars. Our findings will help constrain stellar evolution in the exotic UV upturn phase. (ProQuest: ... denotes formulae/symbols omitted.)
ABSTRACT
We present results of the MUSE-ALMA haloes, an ongoing study of the circumgalactic medium (CGM) of low-redshift galaxies (z ≤ 1.4), currently comprising 14 strong H i absorbers in 5 quasar ...fields. We detect 43 galaxies associated with absorbers down to star formation rate (SFR) limits of 0.01–0.1 M⊙ yr−1, found within impact parameters (b) of 250 kpc from the quasar sightline. Excluding the targeted absorbers, we report a high detection rate of 89 per cent and find that most absorption systems are associated with pairs or groups of galaxies (3–11 members). We note that galaxies with the smallest impact parameters are not necessarily the closest to the absorbing gas in velocity space. Using a multiwavelength data set (UVES/HIRES, HST, MUSE), we combine metal and H i column densities, allowing for derivation of the lower limits of neutral gas metallicity as well as emission-line diagnostics (SFR, metallicities) of the ionized gas in the galaxies. We find that groups of associated galaxies follow the canonical relations of N(H i)–b and Wr(2796)–b, defining a region in parameter space below which no absorbers are detected. The metallicity of the ISM of associated galaxies, when measured, is higher than the metallicity limits of the absorber. In summary, our findings suggest that the physical properties of the CGM of complex group environments would benefit from associating the kinematics of individual absorbing components with each galaxy member.
We present the 3D real-space clustering power spectrum of a sample of ∼600 000 luminous red galaxies measured by the Sloan Digital Sky Survey, using photometric redshifts. These galaxies are old, ...elliptical systems with strong 4000-Å breaks, and have accurate photometric redshifts with an average error of Δz= 0.03. This sample of galaxies ranges from redshift z= 0.2 to 0.6 over 3528 deg2 of the sky, probing a volume of 1.5 h−3 Gpc3, making it the largest volume ever used for galaxy clustering measurements. We measure the angular clustering power spectrum in eight redshift slices and use well-calibrated redshift distributions to combine these into a high-precision 3D real-space power spectrum from k= 0.005 to k= 1 h Mpc−1. We detect power on gigaparsec scales, beyond the turnover in the matter power spectrum, at a ∼2σ significance for k < 0.01 h Mpc−1, increasing to 5.5σ for k < 0.02 h Mpc−1. This detection of power is on scales significantly larger than those accessible to current spectroscopic redshift surveys. We also find evidence for baryonic oscillations, both in the power spectrum, as well as in fits to the baryon density, at a 2.5 σ confidence level. The large volume and resulting small statistical errors on the power spectrum allow us to constrain both the amplitude and the scale dependence of the galaxy bias in cosmological fits. The statistical power of these data to constrain cosmology is ∼1.7 times better than previous clustering analyses. Varying the matter density and baryon fraction, we find ΩM= 0.30 ± 0.03, and Ωb/ΩM= 0.18 ± 0.04, for a fixed Hubble constant of 70 km s−1 Mpc−1 and a scale-invariant spectrum of initial perturbations. The detection of baryonic oscillations also allows us to measure the comoving distance to z= 0.5; we find a best-fitting distance of 1.73 ± 0.12 Gpc, corresponding to a 6.5 per cent error on the distance. These results demonstrate the ability to make precise clustering measurements with photometric surveys.
We measure the sum of the neutrino particle masses using the three-dimensional galaxy power spectrum of the Sloan Digital Sky Survey III (SDSS-III) Baryon Oscillation Spectroscopic Survey Data ...Release 9 the constant MASS (CMASS) galaxy sample. Combined with the cosmic microwave background, supernova and additional baryonic acoustic oscillation data, we find upper 95 per cent confidence limits (CL) of the neutrino mass Σm
ν < 0.340 eV within a flat Λ cold dark matter (ΛCDM) background, and Σm
ν < 0.821 eV, assuming a more general background cosmological model. The number of neutrino species is measured to be N
eff = 4.308 ± 0.794 and
for these two cases, respectively. We study and quantify the effect of several factors on the neutrino measurements, including the galaxy power spectrum bias model, the effect of redshift-space distortion, the cut-off scale of the power spectrum and the choice of additional data. The impact of neutrinos with unknown masses on other cosmological parameter measurements is investigated. The fractional matter density and the Hubble parameter are measured to be
km s−1 Mpc−1 (flat ΛCDM) and
km s−1 Mpc−1 (more general background model). Based on a Chevallier-Polarski-Linder parametrization of the equation-of-state w of dark energy, we find that w = −1 is consistent with observations, even allowing for neutrinos. Similarly, the curvature ΩK and the running of the spectral index αs are both consistent with zero. The tensor-to-scalar ratio is constrained down to r < 0.198 (95 per cent CL, flat ΛCDM) and r < 0.440 (95 per cent CL, more general background model).
The halo of the Milky Way provides unique elemental abundance and kinematic information on the first objects to form in the Universe, and this information can be used to tightly constrain models of ...galaxy formation and evolution. Although the halo was once considered a single component, evidence for its dichotomy has slowly emerged in recent years from inspection of small samples of halo objects. Here we show that the halo is indeed clearly divisible into two broadly overlapping structural components--an inner and an outer halo--that exhibit different spatial density profiles, stellar orbits and stellar metallicities (abundances of elements heavier than helium). The inner halo has a modest net prograde rotation, whereas the outer halo exhibits a net retrograde rotation and a peak metallicity one-third that of the inner halo. These properties indicate that the individual halo components probably formed in fundamentally different ways, through successive dissipational (inner) and dissipationless (outer) mergers and tidal disruption of proto-Galactic clumps.
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