The GHz-Peaked Spectrum radio galaxy 2021+614: Detection of slow motion   in a compact symmetric object
  We have analysed VSOP (VLBI Space Observatory Programme) data at 5 GHz and ground-based VLBI (Very Long Baseline Interferometry) data at 15 GHz for the GHz-Peaked Spectrum (GPS) radio galaxy 2021+614. Its morphology is consistent with it being a compact symmetric source extending over 30 h^-1 pc (H_0 = 100 h km s^-1 Mpc^-1, q_0 = 0.5). From a comparison with earlier observations we have detected an increase in the separation and a decrease in the size of the two most prominent components. We determine the projected speed with which these two components recede from each other to be 0.12+/-0.02 h^-1 c. Given the projected separation of the two components of 16.1 h^-1 pc, the infered kinematic age is 440+/-80 years, measured in the source reference frame. These results provide additional support for the contention that compact symmetric radio objects are young and the precursors of the classical FR I or FR II radio sources. The sizes of individual components appear to contract with time which is not consistent with the self-similar evolution model for peaked spectrum sources.   In order to overcome problems related to the estimation of uncertainties for separation measurements between source components, we have developed and applied a method that compares two uv-data sets obtained at different epochs. This method parametrizes the most important structural change, the increase in separation between components, by rescaling the u and v axis of the amplitude interference pattern. It provides best-fit values for the parameters and uses a bootstrap method to estimate the errors in the parameters. 
Wolfgang Tschager (1), Richard T. Schilizzi (1 and 2), Huub J. A.   R"ottgering (1), Ignas A. G. Snellen (3) and George K. M...