Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001aas...19913822w&link_type=abstract
American Astronomical Society, 199th AAS Meeting, #138.22; Bulletin of the American Astronomical Society, Vol. 33, p.1517
Astronomy and Astrophysics
Astronomy
1
Scientific paper
The NRAO VLBA was used at 5.0 GHz to image 27 FIRST sources in the Boötes field of the NOAO Deep Wide-Field Survey (NDWFS). FIRST sources were selected as being compact (Θ M < 5" ) and bright (S peak > 10 mJy beam-1) at 1.4 GHz, implying a typical position error in one dimension of +/-400 mas at 4σ . For each FIRST source, this position error defines the VLBA search region in a phase-referenced image with a FWHM resolution of 3.3 mas by 1.5 mas. FIRST images of these 27 sources imply that 24 are candidates for containing active galactic nuclei (AGN), 2 are hotspots within a single extended source, and 1 is a jet-like feature adjacent to an AGN candidate. Among the 24 FIRST sources that are AGN candidates, 5 were detected with the VLBA above a typical 6σ threshold of 1.5 mJy beam-1 and with a position error in one dimension of less than +/-2 mas at 1σ . Each VLBA detection has a brightness temperature greater than 107 K and must therefore be an AGN. NDWFS images from data release 1.0 suggest that two of these AGN are hosted by galaxies, while two are probable QSOs. NDWFS images are not yet available for the fifth AGN, a possible compact symmetric object. The 19 AGN candidates not detected with the VLBA could still harbor AGN with S peak < 1.5 mJy beam-1 at 5.0 GHz. Therefore, the AGN content in the radio regime of the Boötes field is at least 21+/-9%. The statistical accuracy of this result is set by the small numbers of AGN candidates observed and detected in this pilot VLBA survey. When complete, the VLBA survey will target about four times as many AGN candidates. Among the 3 FIRST sources in the pilot survey that are not AGN candidates, none were detected with the VLBA. This work used images provided by the NDWFS (Jannuzi & Dey 1999, Asp Conf. 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 Associated Universities, Inc.
Fassnacht Chris D.
Myers Steven T.
Taylor Greg B.
Wrobel Joan M.
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