Statistics of Mg II absorbers (Brice Menard)

Mg II absorbers are known to inhabit the halo of galaxies but their nature has been a matter of debate for more than a decade. Recently, Menard et al. (2011) reported a correlation between Mg II rest equivalent width (EW) and the [O II] emission associated with these systems. They showed that strong Mg II absorbers trace most of the star forming galaxies in the Universe and that the incidence rate of Mg II absorbers, dN/dz, is related to the cosmic density of star formation SFR. If confirmed, the Mg II systems would be a powerful alternative tracer of high redshift star formation. A direct prediction of the relation between Mg II and SFR is that the incidence of strong Mg II absorbers is expected to decrease at z > 2 because of the observed decline in SFR(z). On the other hand, the extrapolation of the measured dN/dz predicts a continued rise towards high redshift (Fig. 2). This critical test requires a large sample of QSOs with NIR spectroscopy.[Add FIRE paper]