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J.M. Wrobel (NRAO), M.A. Garrett (JIVE), R. Morganti (ASTRON)
For starbursts, free-free absorption limits the total brightness temperature Tb of the coextensive thermal and nonthermal radio emission to a few times the electron temperature of about 104~K (Condon, 1992, ARAA, 30, 575). For active galactic nuclei (AGNs), higher brightness temperatures are reached. Sky patches can be filtered for AGN with Tb > 2 \times 105~K through deep observations at a frequency \nu = 1.4~GHz with the NRAO VLBA and GBT. Such filtering observations were recently made, within a patch of the NDWFS Boötes field known from WSRT images to be densely populated with faint radio sources (de Vries et al.\ 2002, AJ, 123, 1784; Morganti & Garrett, 2002, ASTRON Newsletter, No.~17). Any WSRT source that is also detected with the VLBA+GBT cannot be energized by just a starburst. Analysis of the VLBA+GBT data is in progress. Phase referencing to the in-beam calibrator WSRT J142910+352945 yields an rms sensitivity of 9~\muJy~beam-1 and, so far, two clear detections. One is of a 400-\muJy source coincident with WSRT J142934+352858. This AGN is hosted by a candidate high-redshift galaxy, as inferred from the host's apparent drop-out in the BW band of the NDWFS. The other detection locates the 300-\muJy AGN embedded in WSRT J142923+352851. Both detections are astrometrically anchored to the ICRF. This work made use of images provided by the NDWFS (Jannuzi & Dey, 1999, ASP Conference Series, 191, 111), which is supported by NOAO. NOAO is operated by AURA, Inc., under a cooperative agreement with the NSF. NRAO is a facility of the NSF operated under cooperative agreement by AUI.
The author(s) of this abstract have provided an email address for comments about the abstract: jwrobel@nrao.edu
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.