Following Black Hole Scaling Relations Through Gas-Rich Mergers

TL;DR

This study measures black hole masses in merging galaxies using high-resolution spectroscopy, revealing they are overmassive compared to scaling relations and suggesting early merger stages are key for black hole growth.

Contribution

It provides new dynamical black hole mass measurements in merging galaxies and challenges the idea that black hole growth peaks during quasar feedback phases.

Findings

Black holes are overmassive relative to scaling relations.

Black hole growth likely occurs early in mergers.

Gas within the sphere of influence may fuel future activity.

Abstract

We present black hole mass measurements from kinematic modeling of high-spatial resolution integral field spectroscopy of the inner regions of 9 nearby (ultra-)luminous infrared galaxies in a variety of merger stages. These observations were taken with OSIRIS and laser guide star adaptive optics on the Keck I and Keck II telescopes, and reveal gas and stellar kinematics inside the spheres of influence of these supermassive black holes. We find that this sample of black holes are overmassive ($\sim10^{7-9}$ M$_{Sun}$) compared to the expected values based on black hole scaling relations, and suggest that the major epoch of black hole growth occurs in early stages of a merger, as opposed to during a final episode of quasar-mode feedback. The black hole masses presented are the dynamical masses enclosed in $\sim$25pc, and could include gas which is gravitationally bound to the black hole but has not yet lost sufficient angular momentum to be accreted. If present, this gas could in principle eventually fuel AGN feedback or be itself blown out from the system.