High-Frequency Peaked Radio Sources (HFP) from AT20G Catalog and Their Radio Spectra

We present a sample of High-Frequency Peaked Radio Source (HFP) candidates from the AT20G catalog with spectral indices of the optically thick emission region αbelow exceeding $$+0.5$$ , aimed to study their spectral properties. The sample includes 269 objects, about 70 $$%$$ of which are quasars. Using the CATS database, we construct the spectra of the sources and determine their main parameters: the spectral indices below and above the peak ( αbelow , αabove ), the peak frequencies νobs , the flux densities at the peak frequency Sₚₑₐₖ , and the half-widths of the peak in the radio spectra. The spectral flux densities of the sources were obtained at different telescopes and often over different observation epochs. The spectral analysis shows that we are dealing with a sample consisting of HFP sources, whose properties are fairly uniform and whose peak frequencies are νobs>5 GHz. Most of the sources (67 $$%$$ ) have no data at the frequencies below 0.8 GHz. One hundred eighty-seven sources have ultra-inverted spectra ( αbelow>+0.7 ), which make up 3.2 $$%$$ of all the sources in the AT20G catalog and 70 $$%$$ of all the sources in our sample. The calculations show that the sample consists of compact objects, whose radio luminosity at the frequency of 20 GHz lies in the range of 10²³-10³⁰ W Hz ⁻¹ , the angular sizes of the emitting regions of the sources are 0.002–0.25 mas, the linear sizes are from 0.2 to 30 pc. The dependence of the intrinsic peak frequencies of radio sources from their angular sizes is in a good agreement with the previously discovered relation for CSS and GPS objects. Based on the information provided by the CATS database, the radio source variability indices are estimated. A variability of 25 $$%$$ or higher was found for seven quasars, five of which are blazars. A comparison of the redshift dependences ( z ) of R -band magnitudes reveals that most of the HFP galaxies in our sample follow the Hubble relation earlier obtained for the GPS galaxies, and can hence be candidates ‘‘young’’ radio source candidates.