Star formation in AGN hosts in GOODS-N

Abstract

Sensitive <i>Herschel<i/> far-infrared observations can break degeneracies that were inherent to previous studies of star formation in high-<i>z<i/> AGN hosts. Combining PACS 100 and 160 <i>μ<i/>m observations of the GOODS-N field with 2 Ms <i>Chandra<i/> data, we detect ~20% of X-ray AGN individually at >3<i>σ<i/>. The host far-infrared luminosity of AGN with <i>≈<i/> 10<sup>43<sup/> erg s<sup>-1<sup/> increases with redshift by an order of magnitude from <i>z = 0<i/> to <i>z<i/> <i>∼<i/> 1. In contrast, there is little dependence of far-infrared luminosity on AGN luminosity, for 10<sup>44<sup/> erg s<sup>-1<sup/> AGN at <i>z<i/> 1. We do not find a dependence of far-infrared luminosity on X-ray obscuring column, for our sample which is dominated by < 10<sup>44<sup/> erg s<sup>-1<sup/> AGN. In conjunction with properties of local and luminous high-<i>z<i/> 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-<i>z<i/> 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.