Enrichment and pre-heating in intragroup gas from galactic outflows

We examine metal and entropy content in galaxy groups having T_X ≈ 0.5-2 keV in cosmological hydrodynamic simulations. Our simulations include a well-constrained prescription for galactic outflows following momentum-driven wind scalings, and a sophisticated chemical evolution model. Our simulation with no outflows reproduces observed iron abundances in X-ray emitting gas, but the oxygen abundance is too low; including outflows yields iron and oxygen abundances in good agreement with data. X-ray measures of [O/Fe] primarily reflect metal distribution mechanisms into hot gas, not the ratio of Type Ia to Type II supernovae within the group. Iron abundance increases by ∼ ×2 from z ∼ 1 to 0 independent of group size, consistent with that seen in clusters, while [O/Fe] drops by ∼30 per cent. Core entropy versus temperature is elevated over self-similar predictions regardless of outflows due to radiative cooling removing low-entropy gas, but outflows provide an additional entropy contribution below 1 keV. This results in a noticeable break in the L_X-T_X relation below ∼1 keV, as observed. Entropy at R₅₀₀ is also in good agreement with data, and is unaffected by outflows. Importantly, outflows serve to reduce the stellar content of groups to observed levels. Specific energy injection from outflows drops with group mass, and exceeds the thermal energy for ≲0.5-keV systems. Radial profiles from simulations are in broad agreement with observations, but there remain non-trivial discrepancies that may reflect an excess of late-time star formation in central group galaxies in our simulations. Our model with outflows suggests a connection between physical processes of galaxy formation and both pre-heating and enrichment in intragroup gas, though more definitive conclusions must await a model that simultaneously suppresses cooling flows as observed.