The case for hot-mode accretion in Abell 2029

Radiative cooling and active galactic nucleus heating are thought to form a feedback loop that regulates the evolution of low-redshift cool-core galaxy clusters. Numerical simulations suggest that the formation of multiphase gas in the cluster core imposes a floor on the ratio of cooling time (tcool) to free-fall time (tff) at min(tcool/tff) ≈ 10. Observations of galaxy clusters show evidence for such a floor, and usually the cluster cores with min(tcool/tff) ≲ 30 contain abundant multiphase gas. However, there are important outliers. One of them is Abell 2029 (A2029), a massive galaxy cluster (M200 ≳ 1015 M⊙) with min(tcool/tff) ∼ 20, but little apparent multiphase gas. In this paper, we present high-resolution 3D hydrodynamic adaptive mesh refinement simulations of a cluster similar to A2029 and study how it evolves over a period of 1–2 Gyr. Those simulations suggest that A2029 self-regulates without producing multiphase gas because the mass of its central black hole (~ 5 × 10¹⁰ \, M_) is great enough for Bondi accretion of hot ambient gas to produce enough feedback energy to compensate for radiative cooling.