Bibcode
Russell, David M.; Ellison, Sara L.; Benn, Chris R.
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 367, Issue 1, pp. 412-422.
Advertised on:
3
2006
Citations
28
Refereed citations
27
Description
We present a sample of 33 damped Lyman α systems (DLAs) discovered
in the Sloan Digital Sky Survey (SDSS) whose absorption redshifts
(zabs) are within 6000 km s-1 of the quasi-stellar
object's (QSO) systemic redshift (zsys). Our sample is based
on 731 2.5 < zsys < 4.5 non-broad absorption line
(non-BAL) QSOs from Data Release 3 (DR3) of the SDSS. We estimate that
our search is ~100 per cent complete for absorbers with N(HI) >= 2
× 1020cm-2. The derived number density of
DLAs per unit redshift, n(z), within Δv < 6000kms-1
is higher (3.5σ significance) by almost a factor of 2 than that of
intervening absorbers observed in the SDSS DR3, i.e. there is evidence
for an overdensity of galaxies near the QSOs. This provides a physical
motivation for excluding DLAs at small velocity separations in surveys
of intervening `field' DLAs. In addition, we find that the overdensity
of proximate DLAs is independent of the radio-loudness of the QSO,
consistent with the environments of radio-loud and radio-quiet QSOs
being similar.