A wide frequency study of the spectral properties of cores and lobes of radio galaxies

Low-frequency radio arrays are opening a new window for the study of the sky, to characterise both new phenomena and already known classes of sources. In our work, we characterise the spectral properties of the blazar population at low radio frequency, compare the radio and high energy properties of the gamma-ray blazar population, and search for radio counterparts of the unidentified gamma-ray sources. In a previous work (Giroletti et al. 2016), the 6100 square degrees Murchison Widefield Array Commissioning Survey catalogue (MWACS) was cross-correlated with the third catalogue of gamma-ray active galactic nuclei detected by Fermi (3LAC). In this Thesis, we cross-correlate the 24831 square degrees Galactic and Extragalactic All-sky MWA (GLEAM) with the same Fermi catalogue. By comparison to MWACS, GLEAM does not only have a larger sky area, but also a better sensitivity and a wider spectral coverage. The fraction of gamma-ray blazars detected in GLEAM grows to 78%, compared to 35% found in MWACS. Thanks to the spectral coverage of GLEAM and of other existing radio surveys, we studied the blazar spectral properties at low (~200MHz), mid (~1GHz), and high frequency (20GHz with the Australia Telescope 20GHz, AT20G). Compact cores and extended lobes have different spectral properties: at low frequency we can study the extended emission, while at high frequency we can study the core. Therefore, determining blazar spectra in different frequency regimes helps us to disentangle the different contributions of the two components, and provide a proxy for the core dominance. The core dominance of an object is a test for the Unified Model for AGN. Also, it is possible to observe the core emission, using an optimal angular resolution. So we used the FIRST survey, with an angular resolution of 5 arcsec. Therefore we estimated the core dominance. Moreover, we created a simulation of 20000 radio sources to verify our results.