Multifrequency VLBI observations of faint gigahertz peaked spectrum sources

We present the data and analysis of VLBI observations at 1.6, 5 and 15 GHz of a sample of faint gigahertz peaked spectrum (GPS) sources selected from the Westerbork Northern Sky Survey. The 5-GHz observations involved a globa l array of 16 stations and yielded data on the total sample of 47 sources. A subsample of 26 GPS sources with peak frequencies v(p)) 5 GHz and/or peak flux densities S-p > 125 mJy was observed with the VLBA at 15 GHz. A secon d subsample of 29 sources, with v(p) < 5 GHz, was observed at 1.6 GHz using a 14-station global VLBI array, In this way, 44 of the 47 sources (94 per cent) in the sample were observed above and at or below their spectral peak . Spectral decomposition allowed us to identify three, 11, seven and two ob jects as compact symmetric objects, compact doubles, core-jet and complex s ources, respectively. However, many of the sources classified as compact do uble or core-jet sources show only two components making their classificati on rather tentative. This may explain why the strong morphological dichotom y of GPS quasars and galaxies found for radio-bright GPS sources is not as clear in this faint sample.