Spherical accretion in giant elliptical galaxies: multi-transonicity, shocks, and implications on AGN feedback

TL;DR

This study investigates how the combined gravitational potential of massive elliptical galaxies affects spherical accretion flows onto SMBHs, revealing multi-transonic behavior, shocks, and temperature thresholds that influence AGN feedback.

Contribution

It extends previous models by incorporating the full galactic potential and cosmological constant, demonstrating complex flow structures and conditions for accretion in massive ellipticals.

Findings

Galactic potential induces multi-transonic flow topology.

Shocks form in spherical wind flows at higher mass-to-light ratios.

A temperature threshold (~9 million K) limits Bondi accretion initiation.

Abstract

Isolated massive elliptical galaxies, or that are present at the center of cool-core clusters, are believed to be powered by hot gas accretion directly from their surrounding hot X-ray emitting gaseous medium. This leads to a giant Bondi-type spherical/quasi-spherical accretion flow onto their host SMBHs, with the accretion flow region extending well beyond the Bondi radius. In this work, we present a detailed study of Bondi-type spherical flow in the context of these massive ellipticals by incorporating the effect of entire gravitational potential of the host galaxy in the presence of cosmological constant $\Lambda$, considering a five-component galactic system (SMBH + stellar + dark matter + hot gas + $\Lambda$). The current work is an extension of Ghosh \& Banik (2015), who studied only the cosmological aspect of the problem. The galactic contribution to the potential renders the (adiabatic) spherical flow to become {\it multi-transonic} in nature, with the flow topology and flow structure significantly deviating from that of classical Bondi solution. More notably, corresponding to moderate to higher values of galactic mass-to-light ratios, we obtain Rankine-Hugoniot shocks in spherical wind flows. Galactic potential enhances the Bondi accretion rate. Our study reveals that there is a strict lower limit of ambient temperature below which no Bondi accretion can be triggered; which is as high as $\sim 9 \times 10^6 \, K$ for flows from hot ISM-phase, indicating that the hot phase tightly regulates the fueling of host nucleus. Our findings may have wider implications, particularly in the context of outflow/jet dynamics, and radio-AGN feedback, associated with these massive galaxies in the contemporary Universe.