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J.M. Wrobel (NRAO), G.B. Taylor (University of New Mexico), T.A. Rector (University of Alaska), S.T. Myers (NRAO), C.D. Fassnacht (University of California at Davis)
As a step toward investigating the parsec-scale properties of faint extragalactic radio sources, the Very Long Baseline Array (VLBA) was used at 5.0 GHz to obtain phase-referenced images of 76 sources in the NOAO Bootes field. These 76 sources were selected from the FIRST catalog to have peak flux densities above 10 mJy at 5-arcsecond resolution and deconvolved major diameters of less than 3 arcseconds at 1.4 GHz. Fifty-seven of these faint radio sources were identified with accretion-powered radio galaxies and quasars brighter than 25.5 mag in the optical I band. On VLA scales at 1.4 GHz, a measure of the compactness of the faint sources (the ratio of the peak flux density from FIRST to the integrated flux density from the NVSS catalog) spans the full range of possibilites arising from source-resolution effects. Thirty of the faint radio sources, or 39(+9,-7) percent, were detected with the VLBA at 5.0 GHz with peak flux densities above 6sigma ~ 2 mJy at 2-milliarcsecond resolution. The VLBA detections occur through the full range of compactness ratios. The stronger VLBA detections can themselves serve as phase-reference calibrators, boding well for opening up much of the radio sky to VLBA imaging. For the adopted cosmology, the VLBA resolution correponds to 17 pc or finer. Most VLBA detections are unresolved or slightly resolved but one is diffuse and five show either double or core-jet structures; the properties of these latter six are discussed in detail. Three VLBA detections are unidentified and fainter than 25.5 mag in the optical I band; their properties are highlighted because they likely mark optically-obscured active nuclei at high redshift.
For details, please see Wrobel et al. (2005, AJ, 130, 923).
The VLBA is operated by the National Radio Astronomy Observatory, a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.