Atmospheric Circulation in Simulations of the AGN–CGM Connection at Halo Masses ∼1013.5 M ⊙

Abstract

Coupling between active galactic nuclei (AGNs) and the circumgalactic medium (CGM) is critical to the interplay between radiative cooling and feedback heating in the atmospheres of the universe’s most massive galaxies. This paper presents a detailed analysis of numerical simulations showing how kinetic AGN feedback with a strong momentum flux interacts with the CGM. Our analysis shows that large-scale CGM circulation driven by that momentum flux plays an important role in reconfiguring the galactic atmosphere and regulating the atmosphere’s central entropy level. We find that most of the AGN's energy output goes into lifting of circumgalactic gas rather than heating of atmospheric gas within the galaxy, consequently reconfiguring the CGM by replacing low-entropy gas originally in the core with higher-entropy gas from larger radii. Circulation of the CGM on ∼10–100 kpc scales therefore plays a critical role in preventing overcooling of gas in these simulated galaxies, but leads to elevated entropy profiles ∼1–10 kpc compared to the observed entropy profiles of massive elliptical galaxies in the same mass range. The simulations also show that our choices of accretion efficiency and jet opening angle significantly affect the AGN–CGM coupling. Reducing the jet opening angle to one-quarter of the fiducial opening angle increases the jet momentum flux, enabling it to drill through to larger radii without effectively coupling with the CGM at the center (r < 5 kpc). Outflows with a lower momentum flux decelerate and thermalize the bulk of their energy at smaller radii (r ≲ 10 kpc).