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Astron. Astrophys. 360, 887-895 (2000)

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The GHz-peaked spectrum radio galaxy 2021+614: detection of slow motion in a compact symmetric object

W. Tschager 1, R.T. Schilizzi 2,1, H.J.A. Röttgering 1, I.A.G. Snellen 3 and G.K. Miley 1

1 Leiden Observatory, P.O. Box 9513, 2300 RA Leiden, The Netherlands
2 J.I.V.E., P.O. Box 2, 7990 AA Dwingeloo, The Netherlands
3 Institute of Astronomy, Madingley Rd, Cambridge CB3 OHA, UK

Received 17 April 2000 / Accepted 27 June 2000

Abstract

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 [FORMULA] pc. 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 [FORMULA]. Given the projected separation of the two components of [FORMULA] pc, the infered kinematic age is [FORMULA] years, measured in the source reference frame 1. 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.

Key words: radio continuum: galaxies – galaxies: active – galaxies: compact – galaxies: evolution – galaxies: individual: 2021+614

Send offprint requests to: W. Tschager (tschager@strw.LeidenUniv.nl)

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© European Southern Observatory (ESO) 2000

Online publication: August 23, 2000
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