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

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.