Introduction

At this conference on the metal-rich Universe, a talk on damped Lyman-alpha (DLA) systems may seem misplaced, since there is now a considerable literature on these absorption-selected galaxies that describes them as metal-poor (e.g. Pettini 2004 and references therein). Faced with the almost universally sub-solar abundances of DLAs over all redshifts (the average metallicity of DLAs is ~ (1/30) Z0 at z — 3 and —(1/10) ZQ at z — 1), questions have been raised concerning DLA-selection techniques. For example, are we missing a large fraction of metal-rich DLAs due to dust obscuration bias (Ostriker & Heisler 1984)? Or are the bulk of the metals in absorbers below the canonical DLA column-density threshold (Peroux et al. 2006)? In this contribution, I review the latest observations on the possibility of selection bias and discuss whether DLAs can ever be considered as metal-rich.

The Metal-rich Universe, eds. G. Israelian and G. Meynet. Published by Cambridge University Press. © Cambridge University Press 2008.

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Figure 22.1. Metallicities from optically selected DLA surveys (open points) and from the radio-selected CORALS survey (filled points). The dashed line shows the 'dust filter' of Prantzos & Boissier (2000), although this is inconsistent with limits on DLA reddening (Ellison et al. 2005a). Figure adapted from Akerman et al. (2005).

Figure 22.1. Metallicities from optically selected DLA surveys (open points) and from the radio-selected CORALS survey (filled points). The dashed line shows the 'dust filter' of Prantzos & Boissier (2000), although this is inconsistent with limits on DLA reddening (Ellison et al. 2005a). Figure adapted from Akerman et al. (2005).

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