AGN and starbursts at high redshift: High resolution EVN radio observations of the Hubble Deep Field

We present deep, wide-field European VLBI Network (EVN) 1.6 GHz observations of the Hubble Deep Field (HDF) region with a resolution of 0.025 arcseconds. Above the 210 mu Jy/beam (5 sigma) detection level, the EVN clearly detects two radio sources in a field that encompasses the HDF and part of the Hubble Flanking Fields (HFF). The sources detected are: VLA J123633+621133 (a z = 1.013, low-luminosity FR-I radio source located within the HDF itself) and VLA J23642+621331 (a dust enshrouded, optically faint, z = 4.424 starburst system). A third radio source, VLA J123646+621404, is detected at the 4 sigma level. The VLBI detections of all three sources suggest that most of the radio emission of these particular sources (including the dusty starburst) is generated by an embedded AGN.