2004A&A...421..479V

We present a study of the early build-up of dust in high redshift galaxies. The study is based on the analysis of 38 Damped Lyα systems (DLAs) for which we derive the fraction of iron atoms in dust form, f_Fe. The sample is representative of metal-poor galaxies in the redshift range 0.6≤z≤3.4 selected on the basis of their absorption HI column density (N(HI)≥2x10²⁰atoms/cm²). We find that the dust fraction increases with metallicity, from f_Fe≃0 at [Fe/H]~-2dex, up to f_Fe≃0.9 at solar metallicity; the increase is fast below [Fe/H]≃-1dex and mild at higher metallicities. We also find some evidence for an increase of f_Fe with cosmic time; a large fraction of the systems younger than ≃3Gyr has f_Fe≲0.5. These results indicate that the dust-to-metal ratio increases in the course of chemical evolution, at variance with the hypothesis of an approximately constant dust-to-metal ratio, commonly adopted in models of galactic evolution. This hypothesis is consistent with local and high-redshift data only when the metallicity is relatively high ([Fe/H]>-1dex). The results of this work suggest that the main mechanisms of dust formation may be rather sensitive to the level of metallicity attained by a galaxy in the course of its chemical evolution. A metallicity-dependent dust production by SNe II seems to be the most promising mechanism to explain the rise of f_Fe at [Fe/H]≲-1dex.