Star formation in AGN hosts in GOODS-N

TL;DR

This study uses Herschel far-infrared data combined with Chandra X-ray observations to analyze star formation in AGN host galaxies across different redshifts, revealing how star formation correlates with AGN properties and evolution.

Contribution

It provides new insights into the relationship between AGN activity and host star formation over cosmic time using sensitive FIR observations.

Findings

Star formation in AGN hosts increases with redshift, especially for moderate luminosity AGN.

Far-infrared luminosity shows little dependence on AGN luminosity for L2-10<~10^44 erg/s at z>~1.

No significant correlation between FIR luminosity and X-ray obscuring column in the sample.

Abstract

Sensitive Herschel far-infrared observations can break degeneracies that were inherent to previous studies of star formation in high-z AGN hosts. Combining PACS 100 and 160um observations of the GOODS-N field with 2Msec Chandra data, we detect ~20% of X-ray AGN individually at >3sig. The host far-infrared luminosity of AGN with L2-10~10^43erg/s increases with redshift by an order of magnitude from z=0 to z~1. In contrast, there is little dependence of far-infrared luminosity on AGN luminosity, for L2-10<~10^44erg/s AGN at z>~1. We do not find a dependence of far-infrared luminosity on X-ray obscuring column, for our sample which is dominated by L2-10<10^44erg/s AGN. In conjunction with properties of local and luminous high-z AGN, we interpret these results as reflecting the interplay between two paths of AGN/host coevolution. A correlation of AGN luminosity and host star formation is traced locally over a wide range of luminosities and also extends to luminous high z AGN. This correlation reflects an evolutionary connection, likely via merging. For lower AGN luminosities, star formation is similar to that in non-active massive galaxies and shows little dependence on AGN luminosity. The level of this secular, non-merger driven star formation increasingly dominates over the correlation at increasing redshift.