Cooling flows as a reference solution for the hot circumgalactic medium

ABSTRACT The circumgalactic medium (CGM) in 10^12\ M haloes is dominated by a hot phase (T 10^6 K). While many models exist for the hot gas structure, there is as yet no consensus. We compare cooling flow models, in which the hot CGM flows inwards due to radiative cooling, to the CGM of 10^12\, to\, 10^13\ M haloes in galaxy formation simulations from the Feedback in Realistic Environments (FIRE) project at z 0. The simulations include realistic cosmological evolution and feedback from stars but neglect AGN feedback. At both mass scales, CGM inflows are typically dominated by the hot phase rather than by the ‘precipitation’ of cold gas. Despite being highly idealized, we find that cooling flows describe 10^13\ M haloes very well, with median agreement in the density and temperature profiles of 20{\ per\ cent} and 10{\ per\ cent}, respectively. This indicates that stellar feedback has little impact on CGM scales in those haloes. For 10^12\ M haloes, the thermodynamic profiles are also accurately reproduced in the outer CGM. For some of these lower-mass haloes, cooling flows significantly overpredict the hot gas density in the inner CGM. This could be due to multidimensional angular momentum effects not well captured by our one-dimensional cooling flow models and/or to the larger cold gas fractions in these regions. Turbulence, which contributes 10\!-\!40{\ per\ cent} of the total pressure, must be included to accurately reproduce the temperature profiles. Overall, cooling flows predict entropy profiles in better agreement with the FIRE simulations than other idealized models in the literature.