Major Galaxy Mergers and the Growth of Supermassive Black Holes in Quasars

TL;DR

This paper investigates the connection between galaxy mergers and the growth of supermassive black holes in quasars, showing that mergers trigger phases of obscured and unobscured quasar activity linked to SMBH growth.

Contribution

It introduces a physical model connecting galaxy mergers with quasar phases and SMBH growth, supported by observations up to redshift 3.

Findings

The ratio of obscured to unobscured quasars varies with cosmic epoch.

Most SMBH mass growth occurs during the heavily-obscured phase.

Galaxy mergers are causally linked to SMBH accretion and star formation.

Abstract

Despite observed strong correlations between central supermassive black holes (SMBHs) and star-formation in galactic nuclei, uncertainties exist in our understanding of their coupling. We present observations of the ratio of heavily-obscured to unobscured quasars as a function of cosmic epoch up to z~3, and show that a simple physical model describing mergers of massive, gas-rich galaxies matches these observations. In the context of this model, every obscured and unobscured quasar represent two distinct phases that result from a massive galaxy merger event. Much of the mass growth of the SMBH occurs during the heavily-obscured phase. These observations provide additional evidence for a causal link between gas-rich galaxy mergers, accretion onto the nuclear SMBH and coeval star formation.