EVN observations of eleven GHz-Peaked-Spectrum radio sources at 2.3/8.4 GHz

Free access article

Issue		A&A Volume 434, Number 1, April IV 2005


Page(s)		123 - 132
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20041778

A&A 434, 123-132 (2005)
DOI: 10.1051/0004-6361:20041778

EVN observations of eleven GHz-Peaked-Spectrum radio sources at 2.3/8.4 GHz

L. Xiang¹, D. Dallacasa^{2, 3}, P. Cassaro⁴, D. Jiang⁵ and C. Reynolds⁶

¹ National Astronomical Observatories, Chinese Academy of Sciences, 40-5 South Beijing Road, Urumqi 830011, PR China
    e-mail: liux@ms.xjb.ac.cn
² Dipartimento di Astronomia, Universita di Bologna, via Ranzani 1, 40127 Bologna, Italy
    e-mail: dallacasa@ira.cnr.it
³ Istituto di Radioastronomia del CNR, via P. Gobetti 101, 40129 Bologna, Italy
⁴ Istituto di Radioastronomia del CNR, CP 141, 96017 Noto SR, Italy
    e-mail: cassaro@noto.ira.cnr.it
⁵ Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, PR China
    e-mail: djiang@shao.ac.cn
⁶ Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo, The Netherlands
    e-mail: reynolds@jive.nl

(Received 3 August 2004 / Accepted 14 December 2004 )

Abstract
We present results of EVN observations of eleven GHz-Peaked-Spectrum (GPS) radio sources at 2.3/8.4 GHz. These sources are from the classical "bright" GPS source samples with peak flux densities > 0.2 Jy and spectral indices $\alpha < -0.2$ ( $S \propto \nu^{-\alpha}$ ) in the optically thick regime of their convex spectra. Most of the target sources did not have VLBI images at the time this project started. The aim of the work is to find Compact Symmetric Object (CSO) candidates from the "bright" GPS samples. These CSOs play a key role in understanding the very early stage of the evolution of individual radio galaxies. The reason for investigating GPS source samples is that CSO candidates are more frequently found among this class of radio sources. In fact both classes, GPS and CSO, represent a small fraction of the flux limited and flat-spectrum samples like PR+CJ1 (PR: Pearson-Readhead survey, CJ1: the first Caltech-Jodrell Bank survey) and CJF (the Caltech-Jodrell Bank flat spectrum source survey) with a single digit percentage progressively decreasing with decreasing flux density limit. Our results, with at least 3, but possibly more CSO sources detected among a sample of 11, underline the effectiveness of our approach. The three confirmed CSO sources (1133+432, 1824+271, and 2121-014) are characterized by a symmetric pair of resolved components, each with steep spectral indices. Five further sources (0144+209, 0554-026, 0904+039, 0914+114 and 2322-040) can be considered likely CSO candidates. The remaining three sources (0159+839, 0602+780 and 0802+212) are either of core-jet type or dominated by a single component at both frequencies.

Key words: galaxies: nuclei -- galaxies: quasars: general -- radio continuum: galaxies

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