Issue |
A&A
Volume 383, Number 1, FebruaryIII 2002
|
|
---|---|---|
Page(s) | 91 - 97 | |
Section | Cosmology (including clusters of galaxies) | |
DOI | https://doi.org/10.1051/0004-6361:20011738 | |
Published online | 15 February 2002 |
The CORALS survey*
II. Clues to galaxy clustering around
QSOs from
damped Lyman alpha systems
1
European Southern Observatory, Casilla 19001, Santiago 19, Chile
2
SIRTF Science Center, Caltech, California, USA e-mail: lyan@ipac.caltech.edu
3
Astrophysics: Department of Physics, Nuclear and Astrophysics Laboratory, Keble Road, Oxford OX1 3RH, UK e-mail: ihook@gemini.edu
4
Institute of Astronomy, Madingley Rd., Cambridge CB3 0HA, UK e-mail: pettini@ast.cam.ac.uk
5
Astrophysics: Department of Physics, Nuclear and Astrophysics Laboratory, Keble Road, Oxford OX1 3RH, UK e-mail: jvw@astro.ox.ac.uk
6
European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei Munchen, Germany e-mail: pshaver@eso.org
Corresponding author: S. Ellison, sellison@eso.org
Received:
14
August
2001
Accepted:
4
December
2001
We present a list of (
km s-1)
DLAs discovered during the CORALS survey
for absorbers in a radio-selected QSO sample. On the assumption that
DLAs are neither ejecta from the QSO, nor part of the host galaxy
itself, we use the number density statistics of these DLAs
to investigate galaxy clustering near the QSO redshift.
We find that
of
DLAs in our radio-selected QSO
sample is ∼4 times larger
than the number density of intervening DLAs, implying an excess
of galaxies near the QSO. This result is further supported with
the inclusion of the radio-loud QSOs in the FIRST survey, although the
total number of DLAs is still small (4) and the result is currently
only significant at approximately the
level.
Since all of the
DLAs we identify in CORALS
are found towards optically bright (
) QSOs, there is no
strong evidence (based on these limited statistics)
that this population suffers from a severe dust bias.
We compare our results with those from an optically-selected, radio-quiet
QSO sample in order to determine whether there is evidence for an excess
of galaxies around radio-loud versus radio-quiet QSOs. We find that
the
of
DLAs towards radio-quiet QSOs is in agreement with
the number density of intervening absorbers. This result, although
currently limited by the small number statistics of our survey, supports
the conclusion that radio-loud quasars are found
preferentially in rich galaxy environments at high redshift.
Finally, we report that one of the new
DLAs
discovered by CORALS has some residual flux in the base of the
Lyman α trough which may be due to Lyman α emission, either from star
formation in the DLA galaxy
or from gas photoionised by the QSO.
Key words: quasars: general / quasars: absorption lines / galaxies: evolution / galaxies: clusters: general
© ESO, 2002
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