The effect of environment on AGN activity: the properties of radio and
  optical AGN in void, isolated and group galaxies
  The evolution of galaxies depends on their environments. In this work, active
galactic nucleus (AGN) activity in different environments has been studied. The
fractions of radio and optical AGN in four different environments have been
compared using samples of void, isolated, group member, and the brightest group
galaxies (BGGs). Galaxies in voids show significantly lower stellar ages,
concentrations, colours and surface mass densities, and they experience more
one-on-one interactions compared to the isolated galaxies and galaxies in
groups. In order to study pure environmental effects, the biases caused by the
stellar mass and galaxy type quantified by 4000$\AA$ break strength have been
removed. While the results confirm no dependence of the optical AGN activity on
environment in blue galaxies and with lower significance in green galaxies, a
higher fraction of optical AGN has been observed for the massive red galaxies
in voids compared to the galaxies in dense environments. This may be related to
the higher amount of one-on-one interaction observed in the void galaxies, or
it may reflect more fundamental differences in the host galaxies or
environments of the voids. The radio-mode AGN activity increases in dense
environment for red galaxies. No changes in the radio-loud AGN fraction have
been observed for the blue and green galaxies. This shows that the effect of
environment on AGN activity is not significant in the presence of cold gas in
galaxies. We also discuss whether the efficiency of gas accretion depends on
the properties of the host galaxy.
