Supernova Sweeping and Black-Hole Feedback in Elliptical Galaxies

TL;DR

This study investigates how black-hole feedback and supernova heating work together to prevent star formation in massive elliptical galaxies, using X-ray observations to analyze gas properties and feedback mechanisms.

Contribution

It provides new evidence that black-hole outbursts and supernova heating jointly regulate star formation by altering gas cooling and entropy in elliptical galaxies.

Findings

Multiphase ellipticals have tc/tff ~10, indicating precipitation-driven feedback.

Single-phase ellipticals show thermally stable gas with tc/tff > 20, driven by supernova outflows.

One galaxy with powerful jets suggests black-hole accretion mode switching due to feedback.

Abstract

Most of the massive elliptical galaxies in the universe stopped forming stars billions of years ago, even though plenty of hot gas remains available for star formation. Here we present compelling evidence indicating that quenching of star formation depends on both black-hole feedback and Type Ia supernova heating. We analyze Chandra X-ray observations of ten massive ellipticals, five with extended, potentially star-forming multiphase gas and five single-phase ellipticals with no star formation. The ratio of cooling time to freefall time at 1--10 kpc in the multiphase galaxies is tc/tff ~10, indicating that precipitation-driven feedback limits cooling but does not eliminate condensation. In the same region of the single-phase galaxies, the radial profiles of gas entropy are consistent with a thermally stable (tc/tff > 20) supernova-driven outflow that sweeps stellar ejecta out of the galaxy. However, in one of those single-phase ellipticals (NGC 4261) we find tc/tff < 10 at < 300 pc. Notably, its jets are ~50 times more powerful than in the other nine ellipticals, in agreement with models indicating that precipitation near the black hole should switch its fueling mode from Bondi-like accretion to cold chaotic accretion. We conclude by hypothesizing that particularly strong black-hole outbursts can shut off star formation in massive elliptical galaxies by boosting the entropy of the hot gas and flipping the system into the supernova-sweeping state.