Effect of local and large-scale environments on nuclear activity and
  star formation
  Active galactic nuclei (AGN) is one of the main drivers for transition from
star-forming disk to passive spheroidal galaxies. However, the role of
large-scale environment versus one-on-one interactions in triggering different
types of AGN is still uncertain. We present a statistical study of the
prevalence of the nuclear activity in isolated galaxies and physically bound
isolated pairs. For the purpose of this study we considered optically and radio
selected nuclear activity types. We aim to assess the effect of one-on-one
interaction on the fraction of AGN and the role of their large-scale
environment. To study the effect of one-on-one interaction on the fraction of
AGN in isolated galaxy pairs, we compare with a sample of isolated galaxies
homogeneously selected under the same isolation criterion. We examine the
effect of the large-scale environment by comparing with control samples of
single galaxies and galaxy pairs. In general we found no difference in the
prevalence of optical AGN for the considered samples. For massive galaxies, the
fraction of optical AGN in isolated galaxies is slightly higher than that in
control samples. Also the fraction of passives in high mass isolated galaxies
is smaller than in any other sample. Generally, there is no dependence on
optical nuclear activity with local environment. On the other hand, we found
evidence that radio AGN are strongly affected by the local environment. Optical
AGN phenomenon is related to cold gas accretion, while radio AGN is related to
hot gas accretion. In this context, there is more cold gas, fueling the central
optical AGN, in isolated systems. Our results are in agreement with a scenario
where cold gas accretion by secular evolution is the main driver of optical
AGN, while hot gas accretion and one-on-one interactions are the main drivers
of radio AGN activity.
