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Damped Lyα absorbers from dwarf galaxy ejecta
Authors:P E J Nulsen  X Barcons  & A C Fabian
Institution:Institute of Astronomy, Madingley Road, Cambridge CB3 0HA,;Department of Physics, University of Wollongong, Wollongong NSW 2522, Australia,;Instituto de Física de Cantabria (Consejo Superior de Investigaciones Científicas - Universidad de Cantabria), 39005 Santander, Spain
Abstract:It is argued that the formation of a dwarf galaxy causes a massive burst of star formation, resulting in the ejection of most of the available gas from the galaxy as a weakly collimated wind. The ejected gas can give rise to a damped Lyα absorber (DLA). Weakly collimated outflows naturally explain the asymmetric profiles seen in low-ionization absorption lines caused by heavy elements associated with DLAs, where absorption is strongest at one edge of the absorption feature. The shape of the distribution of column densities in the model agrees reasonably well with observations. In particular, the break in slope is caused by external photoionization of the wind. A semi-analytical model for galaxy formation is used to show that, for currently acceptable cosmological parameters, dwarf galaxy outflows can account for the majority of DLA systems and their distribution with redshift. This model also predicts a correlation between velocity structure and metallicity of DLA systems, in qualitative agreement with observations. DLAs do not require many large, rapidly rotating disc galaxies to have formed early on, as in other models for their origin.
Keywords:galaxies: formation  quasars: absorption lines
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