The growth and enrichment of intragroup gas

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 drawn from a cosmological simulation that includes a wellconstrained prescription for momentum-driven, stellar/supernova-powered galactic outflows but no active galactic nucleus (AGN) feedback. Our simulation successfully reproduces the key observed IGrM properties, including X-ray trends, for all but the most massive groups. The z < 1 redshift evolution of these is also consistent with the observations. Contrary to expectations, the simulated groups' IGrM does not suffer catastrophic cooling. Yet, the z = 0 group stellar mass is ~2 × too large. We show that this is due to the build-up of cold gas in the massive galaxies before they are incorporated inside groups. This indicates that other feedback mechanisms must activate in real galaxies once they grow to M_* ≈ a few × 10¹⁰ M_⊙ and that these must be powerful enough to expel a significant fraction of the gas from the galactic haloes. Gentle 'maintenance-mode' AGN feedback would be insufficient to bring the stellar and baryonic fractions into agreement with the observations. Just as importantly, we find that the stellar/supernova-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 abundances and the group X-ray temperature, and these results should be relatively insensitive to the addition of AGN feedback.