Letter to the Editor

Star formation in AGN hosts in GOODS-N ^*

¹ MPE, Postfach 1312, 85741 Garching, Germany e-mail: shao@mpe.mpg.de
² INAF – Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Italy
³ Department of Physics, Durham University, South Road, Durham, DH1 3LE, UK
⁴ European Space Astronomy Centre, Villafranca del Castillo, Spain
⁵ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
⁶ INAF – Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
⁷ IRFU/Service d'Astrophysique, Bât.709, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France
⁸ Pontificia Universidad Católica de Chile, Departamento de Astronomía y Astrofísica, Casilla 306, Santiago 22, Chile
⁹ Instituto de Astrofísica de Canarias, 38205 La Laguna, Spain
¹⁰ Departamento de Astrofísica, Universidad de La Laguna, Spain
¹¹ Department of Astronomy and Astrophysics, 525 Davey Lab, Pennsylvania State University, University Park, PA 16802, USA
¹² Istituto Nazionale di Astronomia, Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
¹³ Dipartimento di Astronomia, Universitá di Padova, 35122 Padova, Italy
¹⁴ Max-Planck-Institut für Plasmaphysik, Boltzmannstraße 2, 85748 Garching, Germany

Received: 31 March 2010
Accepted: 13 May 2010

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 160 μm observations of the GOODS-N field with 2 Ms Chandra data, we detect ~20% of X-ray AGN individually at >3σ. The host far-infrared luminosity of AGN with ≈ 10⁴³ erg s^-1 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 10⁴⁴ erg s^-1 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 < 10⁴⁴ erg s^-1 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.