Where are the Cosmic Metals at z~3?

Abstract

The temperature distribution of the cosmic gas-phase oxygen at z~3 is determined by combining high resolution cosmological simulations with the observed, (rest-frame) V-band galaxy LF. The simulations invoke three different stellar IMFs, a Kroupa (K98), a Salpeter (S) and an Arimoto-Yoshii (AY), spanning a range of a factor of five in chemical yield and specific SNII energy feedback. Oxygen is found in all T phases (cold: logT<~4, warm: logT~4.5, hot: logT>~5), in particular for the (top-heavy) AY IMF. For the K98 and S IMFs, the most important phase is the cold one. Moreover, the cold phase alone contains 1-3 times the mass of oxygen in galactic stars for the three IMFs. The implications of this in relation to DLA studies are discussed. In relation to ``missing metals'' it is found that a significant fraction of the oxygen is located in a warm/hot phase that may be very difficult to detect. Moreover, it is found that less than about 20-25% of the cosmic oxygen is associated with galaxies brighter than M_V~-22, the faintest LBGs probed by current metallicity determinations. From the LBG based, lambda~1500 AA luminosity density history at z>3, the mean oxygen density at z=3 is inferred. Comparing this to the models, it is found that the (solar neighbourhood type) K98 IMF is strongly excluded (too small yield), the S is marginally excluded, and the AY matches the constraint well. The optimal IMF has a yield between the S and AY. A similar conclusion is reached on the basis of the C IV abundance of the moderate density IGM.