Statistical Results from the First Caltech--Jodrell Bank VLBI Survey
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**Session 100 -- AGN: Unified Picture**
*Oral presentation, Friday, January 14, 2:15-3:45, Crystal Forum Room (Crystal City Marriott)*

## [100.02] Statistical Results from the First Caltech--Jodrell Bank VLBI Survey

*T.J.~Pearson, W.~Xu, A.C.S.~Readhead (Caltech), P.~N. Wilkinson, A.~Polatidis (NRAL, Jodrell Bank)*
In the Pearson--Readhead (PR) and Caltech--Jodrell (CJ1) surveys we have
made milliarcsecond-resolution images at $\lambda6$ and $\lambda18$~cm
of the cores of 127 radio sources from a complete sample of 200 objects
with total $\lambda6$~cm flux density $\ge 0.7$~Jy. This large sample is
suitable for a variety of statistical studies, including the
following.\par
(1)~The distribution of $\Delta$PA, the difference in position angle
between parsec-scale and kiloparsec-scale structure, is bimodal with
peaks at $0^\circ$ and $90^\circ$, confirming the result found in a
smaller subsample by Pearson and Readhead. We discuss the differences in
properties of the two types of object, and interpret the distribution in
terms of relativistic beaming of helical jets (cf.~Conway \& Murphy
1993, ApJ, 411, 89).\par
(2)~We present the $\theta$--$z$ (angular size--redshift) diagram for
this sample, and compare it with the results of Kellermann (1993,
Nature, 361, 134) which showed evidence for a deceleration parameter
$q_0=0.5$. In contrast to Kellermann, we find that the the angular
displacement between the unresolved nucleus and the 2\% contour in the
jet does not depend on redshift in the way expected for a standard
measuring rod, and that most parsec-scale jets have a self-similar,
scale-free structure that cannot be used for cosmological inferences.

**Friday
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