A VLBI and MERLIN Survey of faint, compact radio sources

Abstract

We present preliminary results from a VLBI survey at $\lambda=6 $cm of a sample of 35 sources with flux densities of 2 - 100 mJy. These sources were selected from the VLA FIRST survey at $\lambda = 20 $cm, in a 3 degree field around the bright calibrator 1156+295, simply by imposing $S_{20} > 10 $ mJy and $\theta < 5$ arcsec. MERLIN observations at $\lambda 6 $cm detected 70/127 of these sources with a threshold of 2 mJy at 50 mas resolution and the closest 35 of these to the calibrator were observed with the VLBA+EVN in snapshot mode at $\lambda 6 $cm. These sources are a mixture of flat and steep-spectrum sources and include: weak flat-spectrum nuclei of large radio galaxies, low power AGN in nearby galaxies and radio quiet quasars. With these short observations, the sensitivity is limited and most appear as either core-jets or simple point sources on the milliarcsec scale. Nonetheless, it is encouraging that with only 10 minutes observation per source, at least 35% of all sources with $S_{20} > 10 $ mJy can be detected and imaged with global 6cm VLBI.