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ABSTRACT The circumgalactic medium (CGM) in $$\gtrsim 10^{12}\ \mathrm{M}_{\odot }$$ haloes is dominated by a hot phase ($$T \gtrsim 10^{6}$$ 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 $$\sim 10^{12}{\,\rm to\,}10^{13}\ \mathrm{M}_{\odot }$$ haloes in galaxy formation simulations from the Feedback in Realistic Environments (FIRE) project at $$z\sim 0$$. 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 $$\sim 10^{13}\ \mathrm{M}_{\odot }$$ haloes very well, with median agreement in the density and temperature profiles of $$\sim 20{{\ \rm per\ cent}}$$ and $$\sim 10{{\ \rm per\ cent}}$$, respectively. This indicates that stellar feedback has little impact on CGM scales in those haloes. For $$\sim 10^{12}\ \mathrm{M}_{\odot }$$ 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 $$\sim 10{\!-\!}40{{\ \rm per\ cent}}$$ 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. 

Abstract Feedback from supermassive black holes is believed to be a critical driver of the observed color bimodality of galaxies above the Milky Way mass scale. Active galactic nuclei (AGN) feedback has been modeled in many galaxy formation simulations, but most implementations have involved simplified prescriptions or a coarse-grained interstellar medium (ISM). We present the first set of Feedback In Realistic Environments (FIRE)-3 cosmological zoom-in simulations with AGN feedback evolved toz∼ 0, examining the impact of AGN feedback on a set of galaxies with halos in the mass range 10¹²–10¹³M_⊙. These simulations combine detailed stellar and ISM physics with multichannel AGN feedback including radiative feedback, mechanical outflows, and, in some simulations, cosmic rays (CRs). We find that massive (>L*) galaxies in these simulations can match local scaling relations including the stellar mass–halo mass relation and theM_BH–σrelation; in the stronger model with CRs, they also match the size–mass relation and the Faber–Jackson relation. Many of the massive galaxies in the simulations with AGN feedback have quenched star formation and elliptical morphologies, in qualitative agreement with observations. In contrast, simulations at the massive end without AGN feedback produce galaxies that are too massive and form stars too rapidly, are order-of-magnitude too compact, and have velocity dispersions well above Faber–Jackson. Despite these successes, the AGN models analyzed do not produce uniformly realistic galaxies when the feedback parameters are held constant: While the stronger model produces the most realistic massive galaxies, it tends to overquench the lower-mass galaxies. This indicates that further refinements of the AGN modeling are needed.