| Issue |
A&A
Volume 508, Number 1, December II 2009
|
|
|---|---|---|
| Page(s) | 133 - 140 | |
| Section | Extragalactic astronomy | |
| DOI | https://doi.org/10.1051/0004-6361/200811541 | |
| Published online | 15 October 2009 | |
Damped and sub-damped Lyman-α absorbers in z > 4 QSOs *,**
1
Universidade Estadual de Feira de Santana, Av. Transnordestina, s/n, 40036-900, Feira de Santana, BA, Brasil e-mail: rguimara@eso.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
Received:
17
December
2008
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
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