Metallicity evolution of damped Ly{alpha} systems out to z ~ 5. (2012)
Keywords :
Galaxy halo; galaxies: abundances; galaxies: evolution; galaxies: general; galaxies: ISM; quasars: absorption lines
Abstract:We present chemical abundance measurements for 47 damped Ly{alpha} (DLA) systems, 30 at z>4, observed with the Echellette Spectrograph and Imager and the High Resolution Echelle Spectrometer on the Keck telescopes. H I column densities of the DLAs are measured with Voigt profile fits to the Ly{alpha} profiles, and we find an increased number of false DLA identifications with Sloan Digital Sky Survey at z>4 due to the increased density of the Ly{alpha} forest. Ionic column densities are determined using the apparent optical depth method, and we combine our new metallicity measurements with 195 from previous surveys to determine the evolution of the cosmic metallicity of neutral gas. We find the metallicity of DLAs decreases with increasing
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The first sample of targets was drawn from the SDSS-DR3 and SDSS-DR5
surveys for DLA systems performed by Prochaska et al. (2005,
Cat. J/ApJ/635/123) and Prochaska & Wolfe (2009ApJ...696.1543P),
respectively. We restricted the list to sources that were sufficiently
bright such that we could obtain S/N>15 spectra in a non-prohibitive
observing time. After the first few nights, we needed to supplement
the sample with additional z>4 DLAs, and we searched for new z>4
quasars from SDSS-DR7.
In addition to this primary high-redshift quasar sample obtained in
2009-2011, we also include new observations of lower redshift quasars
(2.5<~z<~3.5) obtained in 2008 to augment the number of unbiased
metallicity measurements. The new observations comprise a total of six
nights on the Echellette Spectrograph and Imager (ESI) and seven
nights on High Resolution Echelle Spectrometer (HIRES) on the Keck I
and II 10m telescopes. In Table 1 we present a journal of observations
describing the 50 quasars in our sample.
- VII/270 : SDSS quasar catalog
- VII/258 : Quasars and Active Galactic Nuclei (13th Ed.) (Veron+ 2010)
- II/294 : The SDSS Photometric Catalog, Release 7 (Adelman-McCarthy+, 2009)
- J/A+A/547/L1 : SDSS-III DR9 DLA catalogue (Noterdaeme+, 2012)
- J/A+A/530/A33 : Evolutionary tracks to estimate DLA depletions (Vladilo+,
- J/ApJ/721/1 : Keck ESI observations of Ly{alpha} systems (Penprase+, 2010)
- J/ApJ/683/321 : Metallicities of GRB, DLA, & Ly{alpha} galaxies (Fynbo+, 2008)
- J/ApJ/675/1002 : Proximate DLA systems in SDSS-DR5 (Prochaska+, 2008)
- J/ApJS/171/29 : UCSD/Keck DLA Abundance Database (Prochaska+, 2007)
- J/A+A/473/791 : CIV absorption in DLAs and sub-DLAs systems (Fox+, 2007)
- J/ApJ/636/610 : Damped Ly{alpha} systems at z<1.65 (Rao+, 2006)
- J/ApJ/635/123 : The SDSS-DR3 damped Ly{alpha} survey (Prochaska+, 2005)
- J/AJ/130/1345 : Optical-infrared colors of CORALS QSOs (Ellison+, 2005)
- J/MNRAS/354/L31 : SDSS DR2 QSO and DLA properties (Murphy+, 2004)
- J/PASP/116/622 : SDSS damped Ly{alpha} survey
- J/A+A/370/426 : APM BR J0307-4945 UVES spectrum (Dessauges-Zavadsky+, 2001)
- http://www.sdss.org/ : SDSS home page
