Abstract
We use cosmological hydrodynamical simulations of Milky Way-sized halos with
different feedback strengths or merger histories to investigate the formation
of X-ray luminous coronae. We show that a galactic corona is not a consequence
of hot spherical accretion onto a galaxy but of mergers-induced shock heating
and supernova feedback. Coronae grow inside-out and detach galaxies from the
filamentary network as they outbalance the pressure of cold flows.
Additionally, ram pressure strips cold flows at the intersection of the two
fronts. Coronae thus drive the transition from the cold mode to hot mode
accretion. Our results predict the presence of gas at high temperatures even as
early as $z=3-4$, and in halos of much lower mass than the critical mass for
hot mode accretion suggested by previous simulations and analytical models
(Dekel et al.). All this is quite different from the standard picture in which
diffuse halos are a consequence of the thermalisation of kinetic energy derived
from gravity and/or the geometric effect of cross sections of halos vs.
filaments, and may be more relevant for halos harbouring typical spiral
galaxies. We show that SN feedback impacts the galaxy cold flows connection,
which has also consequences for the large-scale gas supply and may contribute
to galaxy quenching.
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