Obscured GOODS AGN and Their Host Galaxies at z < 1.25: The Slow Black Hole Growth Phase

TL;DR

This study analyzes obscured AGN at z < 1.25 from the GOODS survey, revealing most are in a slow growth phase with black hole growth likely occurred earlier at higher redshifts.

Contribution

It introduces a refined method to estimate bolometric luminosities and black hole masses for obscured AGN, providing insights into their growth stages.

Findings

Most AGN have low Eddington ratios (<0.01).

Black hole masses range from 7 million to 6 billion solar masses.

Black hole growth predominantly occurred at z > 1.

Abstract

We compute black hole masses and bolometric luminosities for 87 obscured AGN in the redshift range 0.25 < z < 1.25, selected from the GOODS deep multi-wavelength survey fields via their X-ray emission. We fit the optical images and obtain morphological parameters for the host galaxy, separating the galaxy from its central point source, thereby obtaining a four-band optical SED for each active nucleus. We calculate bolometric luminosities for these AGN by reddening a normalized mean SED of GOODS broad-line AGN to match the observed central point-source SED of each obscured AGN. This estimate of Lbol has a smaller spread than simple bolometric corrections to the X-ray luminosity or direct integration of the observed multi-wavelength SED, suggesting it is a better measure. We estimate central black hole masses from the bulge luminosities. The black hole masses span a wide range, 7 x 10^6 M_sun to 6 x 10^9 M_sun; the median black hole mass is 5 x 10^8 M_sun. The majority of these AGN have L/L_Edd < 0.01, and we detect no significant evolution of the mean Eddington ratio to z = 1.25. This implies that the bulk of black hole growth in these obscured AGN must have occurred at z > 1 and that we are observing these AGN in a slow- or no-growth state.