Universidade Estadual de Feira de Santana, Av. Transnordestina, s/n, 40036-900, Feira de Santana, BA, Brasil e-mail: firstname.lastname@example.org
2 UPMC Paris 6, Institut d'Astrophysique de Paris, CNRS, 98bis boulevard Arago, 75014 Paris, France
3 Instituto Nacional de Pesquisas Espaciais - INPE, Av. dos Astronautas 1758, 12227-010 S. J. dos Campos, SP, Brasil
4 California Institute of Technology, MS 105-24, Pasadena, CA 91125, USA
5 Inter-University Centre for Astonomy and Astrophysics, Post Bag 4, Ganeshkhind, Pune 411 007, India
6 Europeen Southern Observatory, Karl-Schwarzschild Strasse 2, Garching, Germany
7 Department of Physics, University of Sistan and Baluchestan, 98135 Zahedan, Iran
8 School of Astronomy and Astrophysics, Institute for Research in Fundamental Sciences (IPM), PO Box 193595-5531, Tehran, Iran
Accepted: 7 September 2009
We present the results of a survey of damped (DLA, H i) and sub-damped Lyman-α systems (H i) at along the lines-of-sight to 77 quasars with emission redshifts in the range . Intermediate resolution () spectra were obtained with the Echellette Spectrograph and Imager (ESI) mounted on the Keck telescope. A total of 100 systems with H i were detected of which 40 systems are damped Lyman-α systems for an absorption length of . About half of the lines of sight of this homogeneous survey have never been investigated for DLAs. We study the evolution with redshift of the cosmological density of the neutral gas and find, consistent with previous studies at similar resolution, that decreases at . The overall cosmological evolution of shows a peak around this redshift. The H i column density distribution for H i is fitted, consistent with previous surveys, with a single power-law of index . This power-law overpredicts data at the high-end and a second, much steeper, power-law (or a gamma function) is needed. There is a flattening of the function at lower H i column densities with an index of for the column density range H i. The fraction of H i mass in sub-DLAs is of the order of 30%. The H i column density distribution does not evolve strongly from to .
Key words: Galaxy: evolution / Galaxy: formation / quasars: absorption lines / intergalactic medium / cosmology: observations
The observations reported here were obtained with the W. M. Keck Observatory, which is operated by the California Association for Research in Astronomy, a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration.
© ESO, 2009