Identifying the Obscured Black-Hole Growth Phase of Distant Massive Galaxies

TL;DR

This study combines X-ray and infrared observations to identify heavily obscured AGNs in z~2 dust-obscured galaxies, revealing that supermassive black hole growth was predominantly hidden by gas and dust during this epoch.

Contribution

It introduces new diagnostics based on X-ray and IR data to detect heavily obscured AGNs, advancing understanding of SMBH growth in dust-obscured galaxies at high redshift.

Findings

Most AGN activity in z~2 dust-obscured galaxies is heavily obscured.

SMBH growth at z~2 is often obscured by Compton-thick material.

SMBH growth closely linked to galaxy spheroid development during this epoch.

Abstract

It is well established that a dominant phase in the growth of massive galaxies occurred at high redshift and was heavily obscured by gas and dust. Many studies have explored the stellar growth of massive galaxies but few have combined these constraints with the growth of the supermassive black hole (SMBH; i.e., identified as AGN activity). In this brief contribution we highlight our work aimed at identifying AGNs in z~2 luminous dust-obscured galaxies. Using both sensitive X-ray and infrared (IR)-submillimeter (submm) observations, we show that AGN activity is common in z~2 dust-obscured systems. With a variety of techniques we have found that the majority of the AGN activity is heavily obscured, and construct diagnostics based on X-ray-IR data to identify some of the most heavily obscured AGNs in the Universe (i.e., AGNs obscured by Compton-thick material; N_H>1.5x10^24 cm^-2). On the basis of these techniques we show that SMBH growth was typically heavily obscured (N_H>10^23 cm^-2) at z~2, and find that the growth of the SMBH and spheroid was closely connected, even in the most rapidly evolving systems.