A multi-epoch VLBI survey of the kinematics of CFJ sources
Context. This is the second in a series of papers presenting VLBI observations of the 293 Caltech-Jodrell Bank Flat-spectrum (hereafter CJF) sources and their analysis. Aims. We obtain a consistent motion dataset large enough to allow the systematic properties of the population to be studied. Methods. We present detailed kinematic analysis of the complete flux-density limited CJF survey. We computed 2D kinematic models based on the optimal model-fitting parameters of multi-epoch VLBA observations. This allows us to calculate not only radial, but also orthogonal motions, and thus to study curvature and acceleration. Statistical tests of the motions measured and their reliability were performed. A correlation analysis between the derived apparent motions, luminosities, spectral indices, and core dominance and the resulting consequences is described. Results. With at least one velocity in each of the 237 sources, this sample is much larger than any available before, so it allows a meaningful statistical investigation of apparent motions and any possible correlations with other parameters in AGN jets. The main results to emerge are as follows: - In general motions are not consistent with a single uniform velocity applicable to all components along a jet. - We find a slight trend towards a positive outward acceleration and also adduce some evidence for greater acceleration in the innermost regions. - We find a lack of fast components at physical distances less than a few pc from the reference feature. - Only ~4% of the components from galaxies and <2% of those from quasars undergo large bends i.e. within 15° of ± 90°. - The distribution of radial velocities shows a broad distribution of velocities (apparent velocities up to 30 c). Fifteen percent of the best-sampled jet components exhibit low velocities that may need to be explained in a different manner to the fast motions. - Some negative superluminal motions are seen, and in 15 cases (6%) these are definitely significant. - We find a strong correlation between the 5 GHz luminosity and the apparent velocity. - The CJF galaxies, on average, show slower apparent jet-component velocities than the quasars. - The mean velocity in the VLBA 2 cm survey (Kellermann et al. 2004, ApJ, 609, 539) is substantially higher than in the CJF survey, the ratio could be roughly a factor of 1.5-2. This supports the observed trend toward increasing apparent velocity with increasing observing frequency. Conclusions. This AGN survey provides the basis for any statistical analysis of jet and jet-component properties.
Additional Information© ESO 2008 Received 25 April 2007 / Accepted 26 February 2008. It is a pleasure to thank A. Witzel and T. P. Krichbaum for very inspiring discussions and many helpful comments. We thank the referee K. Kellermann for his advice and comments that significantly improved this manuscript. M. Karouzos carefully proof-read the manuscript. This work was supported by the European Commission, TMR Programme, Research Network Contract ERBFMRXCT96-0034 "CERES". S. Britzen acknowledges support by the Claussen-Simon-Stiftung. This project has been supported by the DLR, project 50QD0101. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. The National Radio Astronomy Observatory is operated by Associated Universities, Inc., under cooperative agreement with the National Science Foundation. The European VLBI Network is a joint facility of European, Chinese, South African and other radio astronomy institutes funded by their national research councils. This work is based on observations with the 100-m telescope of the MPIfR (Max-Planck-Institut für Radioastronomie) at Effelsberg.
Published - BRIaanda08a.pdf