1997A&A...325..943S

Global VLBI observations at 5 GHz of 9 powerful GHz-Peaked-Spectrum (GPS) radio sources from a complete sample of 33 objects (Stanghellini, 1992 (PhD. Thesis), Stanghellini et al., 1996 (in GPS/CSS radio source, in press), 1997, in prep) 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. (1995A&A...302..317F). H₀=100km/s/Mpc, and q₀=0.5 have been assumed throughout this paper.