The origin of dispersion in DLA metallicities.

Abstract : Recent chemical abundance measurements of damped Ly α absorbers (DLAs) revealed an intrinsic scatter in their metallicity of ∼0.5 dex out to z ∼ 5. In order to explore the origin of this scatter, we build a semi-analytic model which traces the chemical evolution of the interstellar matter in small regions of the Universe with different mean density, from over- to underdense regions. We show that the different histories of structure formation in these regions, namely halo abundance, mass and stellar content, are reflected in the chemical properties of the protogalaxies, and in particular of DLAs. We calculate mean metallicity-redshift relations and show that the metallicity dispersion arising from this environmental effect amounts to ∼0.25 dex and is an important contributor to the observed overall intrinsic scatter.