We use idealized three-dimensional hydrodynamic simulations to study the dynamics and thermal structure of the circumgalactic medium ( CGM ) .
Our simulations quantify the role of cooling , stellar feedback driven galactic winds , and cosmological gas accretion in setting the properties of the CGM in dark matter haloes ranging from 10 ^ { 11 } -10 ^ { 12 } M _ { \odot } .
Our simulations support a conceptual picture in which the properties of the CGM , and the key physics governing it , change markedly near a critical halo mass of { M } _ { crit } \approx 10 ^ { 11.5 } \leavevmode \nobreak { M } _ { \odot } .
As in calculations without stellar feedback , above { M } _ { crit } halo gas is supported by thermal pressure created in the virial shock .
The thermal properties at small radii are regulated by feedback triggered when t _ { cool } / t _ { ff } \lesssim 10 in the hot gas .
Below { M } _ { crit } , however , there is no thermally supported halo and self-regulation at t _ { cool } / t _ { ff } \sim 10 does not apply .
Instead , the gas is out of hydrostatic equilibrium and largely supported against gravity by bulk flows ( turbulence and coherent inflow/outflow ) arising from the interaction between cosmological gas inflow and outflowing galactic winds .
In these lower mass halos the phase structure depends sensitively on the outflows ’ energy per unit mass and mass-loading , which may allow measurements of the CGM thermal state to constrain the nature of galactic winds .
Our simulations account for some of the properties of the multiphase halo gas inferred from quasar absorption line observations , including the presence of significant mass at a wide range of temperatures , and the characteristic O vi and C iv column densities and kinematics .
However , we under-predict the neutral hydrogen content of the z \sim 0 CGM .