| Astronomers at JIVE are involved in deep, high resolution surveys of the radio sky. In particular, JIVE leads the development of wide-field analysis techniques as applied to VLBI data. The EVN correlator at JIVE is uniquely equipped to image out the full primary beam of individial VLBI antennas, increasing the typical VLBI field of view by 16 orders of magnitude in terms of real sky coverage. It is thus possible to simultaneously image with VLBI, many faint sub-mJy radio sources with milliarcsecond resolution and microJy sensitivity. The faint radio source population: A significant fraction of the sub-mJy radio source population is believed to located at high-z - at a sensitivity level of 100 microJy, the number of source per square degree at z > 5 is expected to be ~ 100. At these faint flux density levels, much of the radio source population is dominated by extended, moderate-z star forming galaxies. These starbursts are resolved by VLBI but the rarer and perhaps more interesting AGN systems generate compact radio emission, associated with the relativistic outflows generated by accretion onto central massive black holes. Deep, wide-field VLBI observations can therefore be an efficient, and direct way of distinguishing (via brightness temperature arguements) between radio emission generated by star formation and AGN processes. In this way, VLBI can contribute to the cosmic census of AGN (and massive black holes) at the very earliest epochs in the Universe, when the first AGN and black holes began to form. Such observations also probe the accretion history of the early Universe. Crucially, these radio investigations are made free of the effects of dust obscuration. In addition, phase-reference VLBI observations achieve milliarcsecond astrometric precision, and are able to anchor non-radio observations to the International Celestial Reference Frame (ICRF). In crowded, deep fields, such precision astrometry may be useful in identifying faint or obscured sources. |
