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Paper: SB and AGNs in the HDF-N and HFF: Deep, Global VLBI Observations
Volume: 408, The Starburst−AGN Connection
Page: 242
Authors: Chi, S.; Garrett, M.A.; Barthel, P.D.
Abstract: We present the results of deep, wide-field global VLBI 1.4 GHz observations of the Hubble Deep Field North (HDF-N) region and the surrounding Hubble Flanking Fields (HFF). Using the global VLBI network, we attained an r.m.s. noise level of 7 μJy/beam with a 4 mas angular resolution in the inner part of the field. Above the 5σ detection level, we clearly detected 12 compact radio sources. The observations strongly suggest that these sources harbour active galactic nuclei (AGN). Some of the sources show resolved structures, in particular we resolved a jet-like extension emanating from the AGN core of a distant, dust-obscured starburst galaxy. We compared radio, IR, and X-ray luminosities of 12 VLBI detected AGN with starburst sample. The radio/X-ray luminosity correlation clearly presents two separate sub-populations of AGN. One of the sub-population (radio-enhanced AGN) dramatically shows extremely red optical/near-infrared (NIR) colour and even the deepest X-ray survey missed some of the AGN in this group, which imply that these AGN are heavily obscured by dust in the host galaxies. The results clearly demonstrate the power of deep, high-resolution VLBI imaging in discriminating between star-formation and AGN activity in distant, dust-obscured systems.
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