High Frequency Peak Radio Sources from the AT20G Catalogue and Their Radio Spectra

Abstract: A sample of high-frequency peaker (HFP) candidates was formed from the AT20G catalog radio sources with spectral indices of the optically thick emission region $\alpha_{below}$ exceeding +0.5. A study of the spectral properties of the sources in the sample, which included 269 radio sources, was performed. The spectra of the sources were constructed and the spectral indices below $\alpha_{below}$ and above the peak $\alpha_{above}$, the peak frequency $\nu_{obs}$, the flux density at the peak frequency $S_{peak}$, and the peak half-width in the radio spectrum were determined. Analysis of the spectra showed that the sample is fairly homogeneous and consists of HFPs with $\nu_{obs}>5$ GHz. Most sources (67%) do not have data at frequencies below 0.8 GHz. 187 sources have ultra-inverted spectra ($\alpha_{below}>$+0.7), which is 3.2% of all sources in the AT20G catalog and 70% of radio sources in our sample. Optical identification of radio sources in the sample showed that 70% of the hosts are quasars. The sample consists of compact objects with radio luminosity at 20 GHz in the range of $10^{23}$-$10^{30}$ W/Hz, angular sizes of emitting regions of radio sources are 0.002-0.25 mas, projected linear sizes are from 0.2 to 30 pc. The dependence of the peak frequencies of radio sources on their angular sizes is in good agreement with that previously discovered for CSS and GPS sources.