Active Galaxies at Milliarcsecond Resolutionin the NOAO Deep Wide-Field Survey

J.M. Wrobel, T.A. Rector, G.B. Taylor, S.T. Myers (NRAO) C.D. Fassnacht (UC Davis)

ABSTRACT: We are using the NRAO VLBA at 5 GHz to image 206 compact FIRST sources stronger than 10 millijansky (mJy) at 1.4 GHz in the NOAO Deep Wide-Field Survey (NDWFS). Our VLBA survey, now half complete, is not biased with flat-spectrum targets. About one source in three is detected with the VLBA at a resolution of 2 milliarcsecond. Optical identifications to 26 magnitude (mag) are becoming available from the NDWFS. Our VLBA images either locate the active nuclei within the optical hosts, or impose upper limits on emission from the active nuclei. A Chandra survey, in progress, will further constrain the spectral energy distributions of the active nuclei. Some VLBA detections are serving as in-beam phase calibrators for wide-field VLBI imaging of the microjansky sky.

VLBA SURVEY: Our VLBA survey uses phase-referencing to reach FIRST sources [4] in the Bootes and Cetus fields of the NDWFS [2]. The VLBA survey is complete in the Bootes field (shown, 9.0 deg2) and in progress in the Cetus field. Each compact (LAS < 5 arcsecond) FIRST source is observed with the VLBA at 5 GHz for 8 minutes with a total bandwidth of 64 MHz.

VLBA DETECTIONS: In the Bootes field, 30 of 93 sources were detected with the VLBA as stronger than 1.5-2.5 mJy at 2-milliarcsecond resolution.The VLBA detection rate is 32+/-6 percent. Most VLBA detections are unresolved but four apparent doubles, shown below in Stokes I, were discovered.

OPTICAL: Optical identifications to 26 mag are beginning to become available in the Bootes field [2]. At these magnitudes, we expect that the FIRST sources will be completely identified with radio galaxies and quasars. Identifications from early –release NDWFS data (background,1.4 deg2) are described below for four VLBA detections.

SPECTRAL ENERGY DISTRIBUTIONS: Our VLBA images either locate the active nuclei within the optical hosts, or impose upper limits on emission from the active nuclei. We will constrain the spectral energy distributions of the active nuclei by combining the VLBA data with the NDWFS [2] and Chandra [3] data, as those data become available.

DEEP VLBI FIELDS: The stronger VLBA detections in the Bootes field are serving as in-beam phase calibrators for wide-field VLBI imaging of the microjanky sky at 1.4 GHz. Results from a twenty-four-hour pilot study, using the VLBA and the NRAO Green Bank Telescope, are presented at this meeting [1].

J143121.320+332808.95S(FIRST) = 27.3 mJy

J143449.111+354246.98S(FIRST) = 23.3 mJy

J143753.050+351940.08S(FIRST) = 11.1 mJy

J143841.949+335809.48S(FIRST) = 57.2 mJy

J142456.287+352841.80S(FIRST) = 11.2 mJyOptical I ~ 19.8 magQuasar

J142842.556+354326.60S(FIRST) = 19.2 mJyOptical I ~ 19.2 mag

Radio Galaxy

J142910.223+352946.86S(FIRST) = 17.5 mJyOptical I ~ 18.4 magQuasar

J142937.566+344115.69S(FIRST) = 10.6 mJyOptical I ~ 21.5 mag

Radio Galaxy

REFERENCES:[1] Garrett, M.A., Wrobel, J.M., & Morganti, R., this meeting[2] Jannuzi, B.T., & Dey, A. 1999, ASP Conference Series, 191, 111[3] Jones, C., & Murray, S., in preparation[4] White, R.L., et al. 1997, ApJ, 475, 479

This work made use of images provided by the NDWFS (Jannuzi & Dey 1999), 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.