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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. 

Abstract The properties of warm-hot gas around ∼L_*galaxies can be studied with absorption lines from highly ionized metals. We predict Neviiicolumn densities from cosmological zoom-in simulations of halos with masses in ∼10¹²and ∼10¹³M_☉from the Feedback in Realistic Environments (FIRE) project. Neviiitraces the volume-filling, virial-temperature gas in ∼10¹²M_☉halos. In ∼10¹³M_☉halos the Neviiigas is clumpier, and biased toward the cooler part of the warm-hot phase. We compare the simulations to observations from the COS Absorption Survey of Baryon Harbors (or CASBaH) and COS Ultraviolet Baryon Survey (or CUBS). We show that when inferring halo masses from stellar masses to compare simulated and observed halos, it is important to account for the scatter in the stellar-mass–halo-mass relation, especially atM_⋆≳ 10^10.5M_☉. Median Neviiicolumns in the fiducial FIRE-2 model are about as high as observed upper limits allow, while the simulations analyzed do not reproduce the highest observed columns. This suggests that the median Neviiiprofiles predicted by the simulations are consistent with observations, but that the simulations may underpredict the scatter. We find similar agreement with analytical models that assume a product of the halo gas fraction and metallicity (relative to solar) ∼0.1, indicating that observations are consistent with plausible circumgalactic medium temperatures, metallicities, and gas masses. Variants of the FIRE simulations with a modified supernova feedback model and/or active galactic nuclei feedback included (as well as some other cosmological simulations from the literature) more systematically underpredict Neviiicolumns. The circumgalactic Neviiiobservations therefore provide valuable constraints on simulations that otherwise predict realistic galaxy properties.