The black hole - bulge mass relation of Active Galactic Nuclei in the Extended Chandra Deep Field - South Survey

TL;DR

This study investigates whether the local universe's black hole-bulge mass relation holds at redshifts 0.5-1.2, finding that most AGN host galaxies align with local relations, especially bulge-dominated ones, despite many having disks.

Contribution

First measurement of black hole and host galaxy bulge masses at intermediate redshifts using HST imaging and virial black hole mass estimates.

Findings

~80% of AGN hosts follow the local M_BH - M_Bulge relation.

Bulge-dominated hosts are more consistent with local relations.

Most hosts contain significant disks despite alignment with local relations.

Abstract

We present results from a study to determine whether relations, established in the local Universe, between the mass of supermassive black holes (SMBHs) and their host galaxies are in place at higher redshifts. We establish a well-constructed sample of 18 X-ray-selected, broad-line Active Galactic Nuclei (AGN) in the Extended Chandra Deep Field South - Survey with 0.5 < z < 1.2. This redshift range is chosen to ensure that HST imaging is available with at least two filters that bracket the 4000 Angstrom break thus providing reliable stellar mass estimates of the host galaxy by accounting for both young and old stellar populations. We compute single-epoch, virial black hole masses from optical spectra using the broad MgII emission line. For essentially all galaxies in our sample, their total stellar mass content agrees remarkably well, given their BH masses, with local relations of inactive galaxies and active SMBHs. We further decompose the total stellar mass into bulge and disk components separately with full knowledge of the HST point-spread-function. We find that ~80% of the sample is consistent with the local M_BH - M_Bulge relation even with 72% of the host galaxies showing the presence of a disk. In particular, bulge dominated hosts are more aligned with the local relation than those with prominent disks. We further discuss the possible physical mechanisms that are capable building up the stellar mass of the bulge from an extended disk of stars over the subsequent eight Gyrs.