Preliminary Results from the Second Caltech-Jodrell Bank VLBI Survey

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Session 44 -- Radio Galaxies, Jets and Disks
Display presentation, Wednesday, 9:20-6:30, Pauley Room

[44.07] Preliminary Results from the Second Caltech-Jodrell Bank VLBI Survey

G.B. Taylor, A.C.S. Readhead, R.C. Vermeulen, T.J. Pearson, M.H. ~~~ Cohen (Caltech), D.R. Henstock, P.N. Wilkinson, I.W.A. Browne, A. Patnaik (NRAL, Jodrell Bank)

\def\solmass{M$_\odot$} We present preliminary results from the second Caltech-Jodrell Bank VLBI survey (CJ2). This is a Mark 2 snapshot VLBI survey of flat- and peaked-spectrum sources. The CJ2 survey extends the morphological study of the Pearson \& Readhead (1988, ApJ, 328, 114 and Pearson et al.~1993, these proceedings -- hereafter PR) and Caltech-Jodrell Bank (Xu et al.~1992, BAAS, 24, 1300 hereafter CJ) surveys to 400 sources. The CJ2 survey has three new cosmological goals: 1) to populate the proper motion--redshift diagram for superluminal sources; 2) to populate the size--redshift diagram for compact sources (both diagrams can be used to estimate the deceleration parameter, $q_0$); and 3) to search for small-separation gravitationally-lensed systems and hence to look directly for mass concentrations in the unexplored range of $10^6 - 10^9$ \solmass. We expect this survey, like the previous large VLBI surveys, will reveal 5-10\% of the sources to be interesting, unusual objects worth further study.

The CJ2 sample is drawn from the Patnaik et al.~(1992, MNRAS, 254, 655) list of $\sim$900 compact flat-spectrum sources north of $\delta$ = 35\deg with 6 cm flux densities greater than 200 mJy. We have selected the strongest 200 of these sources subject to the further criteria that they are out of the galactic plane ($|b| > 10$\deg), flat-spectrum ($\alpha$ flatter than $-$0.5), and have not been previously observed in the PR or CJ surveys. So far 76 sources have been successfully imaged at 6 cm with $\sim$1 mas resolution and a typical dynamic range of 500:1. The vast majority (63/76) of these sources have core-jet morphologies and are therefore well suited for the cosmological tests described above. Roughly 12\% (9/76) are candidate compact symmetric (CS) sources. This group of sources is not well understood and is of considerable current interest (Readhead et al. 1993, these proceedings).

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