New candidate GHz peaked spectrum and compact steep spectrum sources

Data from a recent Australia Telescope Compact Array (ATCA) program of multi-frequency, multi-epoch monitoring of 202 active galactic nuclei with declinations <+10° have been searched for GHz Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) radio sources. Supplementary data at higher and lower frequencies, where available, have been used to further examine the spectral properties of previously reported and new candidate GPS and CSS sources. The ATCA monitoring program has allowed the variability and polarization properties of sources previously reported as GPS and CSS sources, and the majority of new GPS and CSS candidates, to be investigated, confirming that these are useful diagnostics in discriminating genuine GPS and CSS sources from variable sources that display similar spectra only temporarily. GPS sources are confirmed to be generally more compact, and less polarized, than CSS sources, although CSS sources show evidence for being somewhat less variable than GPS sources at 1.4 and 2.5 GHz. In addition, the widths of GPS spectra are examined, and a significant difference is found in the GPS sample of Snellen et al. (2000) between sources with compact double (CD) or compact symmetric object (CSO) morphologies and sources with other morphologies, in that CD and CSO sources have generally narrower spectra. Possible reasons for this difference are considered.