On the OVI abundance in the circumgalactic medium of low-redshift galaxies

Abstract

We analyse the mass, temperature, metal enrichment, andOVI abundance of the circumgalactic medium (CGM) around z similar to 0.2 galaxies of mass 10(9) M-circle dot < M-* < 10(11.5) M-circle dot in the Illustris simulation. Among star-forming galaxies, the mass, temperature, and metallicity of the CGM increase with stellar mass, driving an increase in the OVI column-density profile of similar to 0.5 dex with each 0.5 dex increase in stellar mass. Observed OVI column-density profiles exhibit a weaker mass dependence than predicted; the simulated OVI abundance profiles are consistent with those observed for star-forming galaxies of mass M-* = 10(10.5-11.5) M-circle dot, but underpredict the observed OVI abundances by greater than or similar to 0.8 dex for lower mass galaxies. We suggest that this discrepancy may be alleviated with additional heating of the abundant cool gas in low-mass haloes, or with increased numerical resolution capturing turbulent/conductive mixing layers between CGM phases. Quenched galaxies of mass M-* = 10(10.5-11.5) M-circle dot are found to have 0.3-0.8 dex lower OVI column-density profiles than star-forming galaxies of the same mass, in qualitative agreement with the observed OVI abundance bimodality. This offset is driven by AGN feedback, which quenches galaxies by heating the CGM and ejecting significant amounts of gas from the halo. Finally, we find that the inclusion of the central-galaxy's radiation field may enhance the photoionization of the CGM within similar to 50 kpc, further increasing the predicted OVI abundance around star-forming galaxies.