High radio frequency sample of bright planetary nebulae in the Southern hemisphere detected in the AT20G survey

© 2015 The Authors. We provide radio spectral properties at high frequencies (1=v (GHz) = 20) for 65 planetary nebulae in the Australia Telescope 20 GHz (AT20G) survey, identified from our list of sources that show flat-spectrum (a >-0.5) and are well resolved at 0.15 arcsec angular size scale. We show that this method very effectively identifies thermal sources like planetary nebulae (and HII regions). In our analysis of the radio spectra of a subset of 37 planetary nebulae, we find no clear evidence of either the excess flux in the optically thin region proposed in the literature, or non-thermal emission. Using a combination of radio spectra, radio interferometric technique and infrared spectra fromWide-field Infrared Survey Explorer, we provide an effective method of identifying further candidates and we list a total of six new planetary nebulae that require follow-up. Together with the list of planetary nebula candidates and the planetary nebulae from the AT20G survey presented in this paper, we provide radio spectra for a complete radio flux limited sample of planetary nebulae at |b| > 1.5 deg in the Southern hemisphere at 20 GHz