VLBI OBSERVATIONS OF 10 COMPACT SYMMETRIC OBJECT CANDIDATES: EXPANSION VELOCITIES OF HOT SPOTS

Abstract

Observations of ten Compact Symmetric Objects ({\\rm CSO}) candidates have\nbeen made with the Very Long Baseline Array at 8.4 GHz in 2005 and with a\ncombined Chinese and European VLBI array at 8.4 GHz in 2009. The 2009\nobservations incorporate for the first time the two new Chinese telescopes at\nMiyun and Kunming for international astrophysical observations. The\nobservational data, in combination with archival VLBA data from previous\nepochs, have been used to derive the proper motions of the VLBI components.\nBecause of the long time baseline of $\\sim$16 years of the VLBI data sets, the\nexpansion velocities of the hot spots can be measured at an accuracy as high as\n$\\sim$1.3 $\\mu$as yr$^{-1}$. Six of the ten sources are identified as CSOs with\na typical double or triple morphology on the basis of both spectral index maps\nand their mirror-symmetry of proper motions of the terminal hot spots. The\ncompact double source J1324+4048 is also identified as a CSO candidate. Among\nthe three remaining sources, J1756+5748 and J2312+3847 are identified as\ncore-jet sources with proper motions of their jet components relating to\nsystemic source expansion. The third source J0017+5312 is likely also a\ncore-jet source, but a robust detection of a core is needed for an unambiguous\nidentification. The kinematic ages of the CSOs derived from proper motions\nrange from 300 to 2500 years. The kinematic age distribution of the CSOs\nconfirm an overabundance of compact young CSOs with ages less than 500 years.\nCSOs with known kinematic ages may be used to study the dynamical evolution of\nextragalactic radio sources at early stages.\n