On the origin of metallicity in Lyman-alpha forest systems

Abstract

In the hierarchical model of structure formation, there is a continuum of halos of various masses and velocity dispersions. In this contribution, we consider the hypothesis that the Lyα absorption lines are produced in two populations of halos in this continuum - in "minihalos" of small velocity dispersions that have never cooled and formed stars, and in large galactic halos with stars and metals. Based on this two-population model for Lyα absorbers, together with chemical history of galactic halos, we investigate whether or not the fraction fm, of Lyα lines associated with metal lines, is understood in terms of fg by the relationship fm ~= fg. If fm is larger than fg, it may be concluded that the intergalactic medium (IGM) experienced a global enrichment at higher z.