Supermassive black holes, star formation and downsizing of elliptical galaxies

TL;DR

This paper enhances chemical evolution models of elliptical galaxies by incorporating feedback from supermassive black holes, explaining observed elemental abundances and galaxy downsizing phenomena.

Contribution

It introduces a model that links black hole growth feedback to star formation efficiency, accounting for observed chemical and evolutionary properties of ellipticals.

Findings

Black hole feedback explains Mg/Fe overabundance in ellipticals.

Galaxy downsizing correlates with black hole activity and star formation efficiency.

Different star formation modes are needed for various galaxy mass ranges.

Abstract

The overabundance of Mg relative to Fe, observed in the nuclei of bright ellipticals, and its increase with galactic mass, poses a serious problem for all current models of galaxy formation. Here we improve on the one-zone chemical evolution models for elliptical galaxies by taking into account positive feedback produced in the early stages of super-massive central black hole growth. We can account for both the observed correlation and the scatter if the observed anti-hierarchical behaviour of the AGN population couples to galaxy assembly and results in an enhancement of the star formation efficiency which is proportional to galactic mass. At low and intermediate galactic masses, however, a slower mode for star formation suffices to account for the observational properties.