On the connection between radio and gamma-ray emission in Active Galactic Nuclei

The extragalactic gamma-ray sky is largely dominated by radio-loud active galactic nuclei (AGN). In particular, the population of blazars represents almost 97 % of the gamma-ray emitting AGN. Blazars, the most extreme class of Active Galactic Nuclei (AGNs), are observed at almost the full electromagnetic spectrum from radio to gamma-ray band. A connection between the radio and gamma-ray emission in blazars has long been suspected, and has received renewed attention during the era of the Fermi Large Area Telescope (LAT) . It is straightforward to demonstrate a statistically significant correlation between observed gamma-ray and radio luminosities or flux densities, as was done during the era of the EGRET instrument. Recent studies using LAT data and concurrent or nearly concurrent radio data provide strong evidence for an intrinsic correlation. In this thesis we have searched for a correlation between radio and gamma-rays emissions in a sample of 174 blazars extracted from the 2FGL catalogue, of which 132 quasars and 7 BLLac, with the predominance of sources in the Southern Emisphere, associated to radio sources with F5GHz < 6 Jy, extracted from the PKS Catalog Cat90. Using the correlation between the brightness and the radio VHE and considering the expected sensitivity of the future gamma-rays telescope CTA, we have also estimated that with this system of telescopes will be possible to reveal at least 82 radio galaxies, extracted from various catalogs radio to the frequency of 5 GHz. Definitely a considerable increase in number respect to those actually observed with HESS and MAGIC telescopes. This number, which is therefore of the order of hundreds, is an estimate because both sites that the configurations of the telescopes of the CTA are not yet fully defined. From the analysis of the estimate of the distribution of radio galaxies as a function of the redshift we have also observed that the majority of them is located at distances z between 0.01 and 0.05, so relatively close.