Deep, wide-field, global VLBI observations of the Hubble deep field north (HDF-N) and flanking fields (HFF)

¹ Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
e-mail: pdb@astro.rug.nl
² Joint Institute for VLBI in Europe (JIVE), PO Box 2, 7990 AA Dwingeloo, The Netherlands
³ Netherlands Foundation for Research in Astronomy (ASTRON), PO Box 2, 7990 AA Dwingeloo, The Netherlands
⁴ Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Mail number H39, PO Box 218, Hawthorn, Victoria 3122, Australia
⁵ Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands

Received: 23 November 2012
Accepted: 21 December 2012

Abstract

Context. Dust is commonly present in weakly radio emitting star-forming galaxies and this dust may obscure the signatures of accreting black holes in these objects.

Aims. We aim to uncover weak active galactic nuclei, AGN, in the faint radio source population by means of deep high-resolution radio observations.

Methods. VLBI observations with a world-wide array at unparallelled sensitivity are carried out to assess the nature of the faint radio source population in the Hubble deep field north and its flanking fields.

Results. Images of twelve compact, AGN-driven radio sources are presented. These represent roughly one quarter of the detectable faint radio source sample. Most, but not all of these low power AGN have X-ray detections.

Conclusions. The majority of the faint radio source population must be star-forming galaxies. Faint AGN occur in a variety of (distant) host galaxies, and these are often accompanied by a dust-obscured starburst. Deep, high-resolution VLBI is a unique, powerful technique to assess the occurrence of faint AGN.