Physical Properties of AGN and their Host Galaxies in z~4 Protoclusters

The environment is one of the main drivers of galaxy and super-massive black hole (SMBH) evolution across cosmic time. To understand the growth of both galaxies and SMBHs, it is key to study the progenitors of the galaxy clusters we see today, where such environmental effects appear most clearly. These vast unvirialized structures, known as protoclusters (PCs), have a high abundance of massive gas reservoirs and a high rate of galaxy mergers, both of which are known to trigger high star-formation activity. These same mechanisms may foster SMBH growth, but it is still unclear to which extent environment affects the accretion episodes at z > 2. Several studies of z > 2 PCs have found that, in contrast to low-redshift clusters, they exhibit higher fractions of active galactic nuclei (AGN) and star-forming galaxies compared to the field. However, it is difficult to compare all the results in literature, since they adopt different methods for selecting AGN, as well as different sensitivity limits in their data. This thesis aims at conducting a statistical study of the AGN and host galaxy properties in the DRC and SPT2349-56 PCs at z ∼ 4, which are selected as overdensities of dusty star-forming galaxies (DSFGs). I analysed the physical properties, mainly stellar mass and SFR, of the spectroscopically confirmed DSFG and AGN members of these structures through spectral energy distribution (SED) fitting with X-CIGALE, fixing common parameter grids for each in the two PCs. To establish a comparison between the properties of DSFGs and AGN-hosts in the PCs and in the field, I have selected a coeval control sample of them in the COSMOS field. The results comparing the Bayesian probability distributions of both populations through the Anderson-Darling (AD) statistic suggest that the stellar mass of PC AGN is significantly lower than that of the field AGN, suggesting that PC AGN are more easily triggered in PC due to the higher rate of mergers and/or massive gas reservoirs.