Dust obscuration of DLA galaxies
Abstract
We show that the extinction of quasar absorbers increases exponentially with the logarithmic column density of any volatile metal (e.g. zinc), with a characteristic turning point above which the quasars are severely dimmed. We derive the relation between extinction, hi column density (n_{HI}), metallicity (z ≡ n_{znii}/n_{HI}), and fraction of iron in dust [f_{Fe}(z)] in damped Lyman α (dla) systems. We use this relation to estimate the effect of dust obscuration on the statistical distributions of n_{HI} and z measured in magnitudelimited surveys of DLAs. In the redshift range where the measurements of zinc column densities have sufficient statistics (1.8 ≤ z ≤ 3) we find that the obscuration bias affects the shapes of the observed distributions. The metallicity distribution is particularly affected by the bias, which hampers the detection of DLA galaxies with near solar metallicity. Our results perfectly reproduce, without tuning the dust parameters, the DLA observational threshold log n({znii}) {[cm^{2}]} ≲ 13.15 found by boissé and collaborators in 1998, in terms of a rapid rise of the obscuration. Our predictions of the effects of the bias on the statistics of DLAs are consistent with observational results obtained from unbiased surveys of radioselected quasars.
 Publication:

IAU Colloq. 199: Probing Galaxies through Quasar Absorption Lines
 Pub Date:
 March 2005
 DOI:
 10.1017/S1743921305002772
 arXiv:
 arXiv:astroph/0510216
 Bibcode:
 2005pgqa.conf..325V
 Keywords:

 Astrophysics
 EPrint:
 To appear in "Probing Galaxies through Quasar Absorption Lines", Proc. IAU Coll.No.199, 2005, eds. P.R.Williams, C.Shu, and B.Menard, 6 pages, 4 figures