Black hole feedback in a multiphase interstellar medium

TL;DR

This study uses high-resolution simulations to explore how ultrafast outflows from supermassive black holes interact with a multiphase interstellar medium, revealing that gas clumpiness significantly influences feedback effectiveness and SMBH growth.

Contribution

It demonstrates the importance of gas phase structure in black hole feedback, highlighting the role of porosity in energy leakage and SMBH mass regulation.

Findings

Shocked UFOs escape through low-density channels in clumpy media.

High-density gas is less affected and may continue inward flow.

Multiphase ISM effects are likely under-resolved in current cosmological models.

Abstract

Ultrafast outflows (UFOs) from supermassive black holes (SMBHs) are thought to regulate the growth of SMBHs and host galaxies, resulting in a number of observational correlations. We present high-resolution numerical simulations of the impact of a thermalized UFO on the ambient gas in the inner part of the host galaxy. Our results depend strongly on whether the gas is homogeneous or clumpy. In the former case all of the ambient gas is driven outward rapidly as expected based on commonly used energy budget arguments, while in the latter the flows of mass and energy decouple. Carrying most of the energy, the shocked UFO escapes from the bulge via paths of least resistance, taking with it only the low-density phase of the host. Most of the mass is however in the high-density phase, and is affected by the UFO much less strongly, and may even continue to flow inwards. We suggest that the UFO energy leakage through the pores in the multiphase interstellar medium (ISM) may explain why observed SMBHs are so massive despite their overwhelmingly large energy production rates. The multiphase ISM effects reported here are probably under-resolved in cosmological simulations but may be included in prescriptions for active galactic nuclei feedback in future simulations and in semi-analytical models.