The growth and enrichment of intragroup gas

Abstract

The thermal and chemical properties of the hot diffuse intragroup medium (IGrM) provide important constraints on the feedback processes associated with massive galaxy formation and evolution. Here we explore these constraints via a detailed analysis of the global properties of simulated z<3 galaxy groups from a cosmological simulation that includes a well-constrained prescription for stellar/supernovae-powered galactic outflows but no AGN feedback. Our aims are to (a) establish a baseline against which we will compare future models; (b) identify model successes due to stellar/supernovae-powered outflows; and (c) pinpoint features that signal the need for, and constrain the nature of, AGN feedback. Our simulation successfully reproduces key observed z=0 group IGrM properties, including the various X-ray Lx - Tx - entropy scaling relations, for all but the most massive groups. The z<1 redshift evolution of these also agree with observations. Contrary to expectations, the simulated groups' IGrM does not suffer catastrophic cooling. Yet, the z=0 group stellar mass is ~ 2X too large. This is due to the build-up of cold gas in the massive galaxies before they are incorporated inside groups. This in turn indicates that other feedback mechanisms must activate in real galaxies once their stellar masses grow to a few X 10^{10} M_sun. We show that these must be powerful enough to expel a significant fraction of the gas from the galactic halos. Gentle maintenance-mode (quenching) AGN feedback, as seen in galaxy clusters, will not do. Just as importantly, we find that the stellar/supernovae-powered winds are essential for understanding the IGrM metal abundances. Our simulation is able to reproduce the observed relationship between the global IGrM iron and silicon abundance and the group X-ray temperature, and these results ought to be relatively insensitive to the addition of AGN feedback.