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Astron. Astrophys. 325, 943-953 (1997)

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A VLBI study of GHz-peaked-spectrum radio sources

I. VLBI images at 6 cm

C. Stanghellini 1, 6, C.P. O'Dea 2, S.A. Baum 2, D. Dallacasa 3, 5, R. Fanti 4, 5 and C. Fanti 4, 5

1 Istituto di Radioastronomia del CNR, C.P. 141, I-96017 Noto SR, Italy
2 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
3 Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo, The Netherlands
4 Dipartimento di Fisica, Università degli Studi, via Irnerio 46, I-40126 Bologna, Italy
5 Istituto di Radioastronomia del CNR, Via Gobetti 101, I-40129 Bologna, Italy
6 Visitor at the Space Telescope Science Institute, Baltimore, USA

Received 10 February 1997 / Accepted 24 March 1997


Global VLBI observations at 5 GHz of 9 powerful GHz-Peaked-Spectrum (GPS) radio sources from a complete sample of 33 objects (Stanghellini 1992, Stanghellini et al. 1996, 1997) are presented. These sources have higher turnover frequencies and smaller overall sizes than Compact Steep-Spectrum (CSS) radio sources, but they are probably related objects with the apparent differences due to a different density of the ambient medium and/or a different age.

The GPS radio sources presented here show a variety of morphologies and have angular sizes ranging from a few to a hundred mas, corresponding to projected linear sizes from a few to hundreds of parsecs.

GPS quasars are rather compact and show core-jet or complex structures and may appear shortened by projection. In contrast, the GPS radio galaxies have larger sizes and exhibit a combination of jets/hot-spots/lobes on both sides of a putative center of activity. Therefore all the radio galaxies observed here can tentatively be classified as Compact Symmetric Objects (CSO). Observations at another frequency (at least) are needed to locate the core, confirm the classification and determine the spectral index of the various components.

Asymmetries in the flux densities and structures of the two opposite sides of our candidate CSO's are more likely produced by interaction with the ambient medium rather than by relativistic beaming.

Morphological properties of the sources in this sample are similar to those found in the smaller CSS by Dallacasa et al. (1995).

H0 =100 km sec-1 Mpc-1, and q0 =0.5 have been assumed throughout this paper.

Key words: galaxies: active – quasars: general – radio continuum: galaxies

Send offprint requests to: C. Stanghellini

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© European Southern Observatory (ESO) 1997

Online publication: April 28, 1998