Chandra investigation of 3CRR radio sources at high redshift

In this thesis the main goal is to investigate the nuclear regions of high-redshift AGN, in order to characterize their X-ray properties and make a comparison with sources at lower redshifts. In the local Universe, a correlation between accretion estimated with the X-ray luminosity between 2-10keV and with the [OIII] IR emission, has been inferred. It is intriguing to observe if this is still valid for the AGN at high redshifts, even if the observation for this sources are more challenging. For this purpose, I proceeded reducing and analysing the X-ray data available in the Chandra public archive for all the sources at z>1 in the 3CRR catalog. This catalog is well observed in all the spectral range, but the X-ray band permits the investigation of the nuclear energetic processes at scales ranging from the kpc to (less than)pc. In addition, a systematic qualitative imaging has been used has a guiding tool during the analysis. In two sources a clear sign of rich environment was visible. Almost all the objects were well represented by a simple absorbed power law model, with the exception of three objects which showed other features (i.e., the Fe line and a thermal component). The luminosity obtained were compared to the [OIII] and they showed a discrepancy. Being aware of the observational limits in the X-ray band and suspecting an observational bias, an investigation based on the IR absorption was carried on. From this scrutiny emerged that most of the radio galaxies, due to their complexity, are more absorbed than the X-ray analysis managed to find. Assuming the existence of this bias and removing the biased objects from the sample, the X-ray and O[III] luminosity are in agreement. Doing a comparison with the radio galaxies at lower redshift studied by Macconi et al. (2020), the objects in my sample successfully reproduce the same correlation, shifted at higher accretion values.