Issue |
A&A
Volume 458, Number 2, November I 2006
|
|
---|---|---|
Page(s) | 427 - 439 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20065372 | |
Published online | 12 September 2006 |
The evolution of Lyman α
absorbers in the redshift range
1
Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany e-mail: [ejanknecht;dreimers]@hs.uni-hamburg.de
2
Departamento de Astronomia, Universidad de Chile, Casilla 36, Santiago, Chile e-mail: slopez@das.uchile.cl
3
Center for Astrophysics and Space Sciences, University of California, San Diego, MS 0424, La Jolla, CA 92093-0424, USA e-mail: tytler@ucsd.edu
Received:
6
April
2006
Accepted:
28
July
2006
We investigate the evolution and the statistical properties
of the Ly α absorbers of the intergalactic medium (IGM)
in the largely unexplored redshift range .
We use high-resolution (
) UV (STIS) and optical (VLT/UVES
and Keck/HIRES) spectra of nine bright quasars with
.
The Ly α lines detected in the lines of sight (LOS) towards these quasars
are evaluated with a software package which determines simultaneously
the quasar continuum and the line profiles.
The main results for the combined Ly α line sample are summarized
as follows:
1. The evolution of the number density of the absorbers can be described
by the power law
.
The number density of the low column density lines
(
cm-2)
decreases with decreasing z with
in the interval
. A comparison with results at higher redshifts shows
that it is decelerated in the explored redshift range
and turns into a flat evolution for
.
The stronger absorbers (
cm-2)
thin out faster (
).
The break in their evolution predicted for
cannot be seen down to
. On the other hand, a comparison with values
from the literature for the local number density gives a hint that this break
occurs at lower redshift.
2. The distribution of the column densities of the absorbers is complete
down to
cm-2. It can be approximated
by a single power law with the exponent
over almost
three orders of magnitude. β is redshift independent.
3. The Ly α lines with lower column densities
as well as the higher column density lines show marginal clustering
with a
significance over short distances (
km s-1
and
km s-1, respectively). We do not see any difference
in the clustering with either column density or redshift.
4. The distribution of the Doppler parameters has a mean value
of
km s-1. This value is typical
for the analyzed region. It does not change significantly with z.
Key words: cosmology: observations / intergalactic medium
© ESO, 2006
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