Galaxy And Mass Assembly (GAMA): The effect of galaxy group environment
  on active galactic nuclei
  In galaxy clusters, efficiently accreting active galactic nuclei (AGN) are
preferentially located in the infall regions of the cluster projected
phase-space, and are rarely found in the cluster core. This has been attributed
to both an increase in triggering opportunities for infalling galaxies, and a
reduction of those mechanisms in the hot, virialised, cluster core. Exploiting
the depth and completeness ($98\,$per cent at $r<19.8\,$mag) of the Galaxy And
Mass Assembly survey (GAMA), we probe down the group halo mass function to
assess whether AGN are found in the same regions in groups as they are in
clusters. We select 451 optical AGN from 7498 galaxies with
$\log_{10}(M_*/\text{M}_\odot) > 9.9$ in 695 groups with $11.53\leq
\log_{10}(M_{200}/\text{M}_\odot) \leq 14.56$ at $z<0.15$. By analysing the
projected phase-space positions of these galaxies we demonstrate that when
split both radially, and into physically derived infalling and core
populations, AGN position within group projected phase-space is dependent on
halo mass. For groups with $\log_{10}(M_{200}/\text{M}_\odot)>13.5$, AGN are
preferentially found in the infalling galaxy population with $3.6\sigma$
confidence. At lower halo masses we observe no difference in AGN fraction
between core and infalling galaxies. These observations support a model where a
reduced number of low-speed interactions, ram pressure stripping and
intra-group/cluster medium temperature, the dominance of which increase with
halo mass, work to inhibit AGN in the cores of groups and clusters with
$\log_{10}(M_{200}/\text{M}_\odot)>13.5$, but do not significantly affect
nuclear activity in cores of less massive structures.
