Hot gas haloes around disc galaxies: O vii column densities from galaxy formation simulations

Abstract

Numerical models of disc galaxy formation predict the existence of extended, hot ( T~10^6 K) gas haloes around present day spirals. The X-ray luminosity of these haloes is predicted to increase strongly with galaxy mass. However, searches for their X-ray emission have not been successful so far. We calculate the all sky O VII column density distributions for the haloes of three Milky Way like disc galaxies, resulting from cosmological high-resolution, N-body/gasdynamical simulations. We perform calculations both including the disc gas and without it, so the disc contribution to the column density is quantified. It is found that the column densities estimated for Milky Way-like galaxies are just below the observational upper limit, making a test of the hot halo paradigm likely within observational reach.