The environment of radio sources in the VLA-COSMOS Survey field
  Several problems regarding the process of galaxy formation are still open.
One of them is the role played by AGN phenomena in contributing to galaxy
build-up and to Star Formation (SF) quenching. On the other hand, the theory of
AGN formation predicts these phenomena to be correlated with the host-galaxy
environment, thus opening for links between SF quenching, environment and AGN
phenomena in the galaxy formation paradigm. This work is focused on the study
of the correlation between environmental density and radio AGN presence. Using
data from the photometric COSMOS survey and the radio 1.4GHz VLA-COSMOS, a
sample of radio AGNs has been defined. The environment has been studied
throughout the use of the richness distributions inside a parallelepipedon with
base side of 1 Mpc and height proportional to the photometric redshift
precision. Richness distributions have been compared as a function of both the
redshift and the relative evolution of the stellar masses of galaxies and AGN
hosts up to $z=2$. Radio AGNs are always located in environments that are
significantly denser than those around galaxies in which radio emission is
absent. Therefore, the environment seems to enhance the probability of a galaxy
to host a radio AGN. Moreover, a distinction between high power and low power
radio AGNs leads to the conclusion that the significance in the environmental
effect is maintained only for low power radio sources. By studying the
evolution of stellar masses it is possible to conclude that radio AGN presence
is a phenomenon related to quiescent galaxies up to $z=2$, with a significant
increase of the fraction of quiescent galaxies hosting a radio AGN with
decreasing redshift. Hints of an environmental effect are present. The results
found with this work lead to conclude that denser environments play a
significant role in enhancing the probability of a galaxy to host a low power
radio AGN.
