The M_BH-M_star relation of obscured AGNs at high redshift

TL;DR

This study detects broad Halpha emission in high-redshift obscured AGNs, estimating their black hole and host galaxy masses, and finds they align with the local M_BH-M_star relation, suggesting an advanced evolutionary stage.

Contribution

First measurement of the M_BH-M_star relation for obscured high-z AGNs selected by X-ray luminosity, showing they follow the local relation unlike other samples.

Findings

Obscured high-z AGNs are consistent with the local M_BH-M_star relation.

These AGNs are likely in an advanced evolutionary stage.

Their nuclear activity may be recently revived by galaxy interactions.

Abstract

We report the detection of broad Halpha emission in three X-ray selected obscured AGNs at z=1-2. By exploiting the Halpha width and the intrinsic X-ray luminosity, we estimate their black hole masses, which are in the range 0.1-3x10^9 Msun. By means of multi-band photometric data, we measure the stellar mass of their host galaxy and, therefore, infer their M_BH/M_star ratio. These are the first obscured AGNs at high-z, selected based on their black hole accretion (i.e. on the basis of their X-ray luminosity), that can be located on the M_BH-M_star relation at high-z. All of these obscured high-z AGNs are fully consistent with the local M_BH-M_star relation. This result conflicts with those for other samples of AGNs in the same redshift range, whose M_BH/M_star ratio departs significantly from the value observed in local galaxies. We suggest that the obscured AGNs in our sample are in an advanced evolutionary stage, have already settled onto the local M_BH-M_star relation, and whose nuclear activity has been temporarily revived by recent galaxy interactions.