SDSS-IV MaNGA: New benchmark for the connection between stellar angular
  momentum and environment: a study of about 900 groups/clusters
  It has been observed that low redshift early-type galaxies can be separated
into slow and fast rotators according to a proxy of specific stellar angular
momentum, $\lambda_{R_e}$. Detailed studies of a handful of nearby clusters
have shown that slow rotators are generally found at the centres of clusters
where the number density is highest, whereas the fast rotators trace the trend
followed by early-type galaxies of increasing in number with local density. In
this paper, we study the environmental distribution of slow and fast rotators
using the stellar kinematics of about 3900 galaxies from the Sloan Digital Sky
Survey's Mapping Nearby Galaxies at Apache Point Observatory survey. For
galaxies in groups closer than $z=0.08$ that are not observed with MaNGA but
satisfy the necessary conditions for slow rotators, we visually assign
slow/fast rotator classifications to obtain a complete sample. Our final
catalogue contains about 900 groups of five or more members. We observe the
kinematic morphology-density (kT-$\Sigma$) relation for each group and find an
increasing fraction of massive slow rotators with increasing number density. We
provide evidence suggesting that the observed lack of trends in angular
momentum with environment at fixed stellar mass is partly because the maximum
density varies between clusters, and that the locations of massive slow
rotators are strongly correlated with peak densities in galaxy groups and
clusters. We conclude that the (projected) number density relative to the
cluster peak is more fundamental than the absolute number density in
influencing the abundance of slow rotators. We find that the kT-$\Sigma$
relation does exist at fixed stellar mass, and we rule out the hypothesis that
the kT-$\Sigma$ relation is a result of dynamical friction alone, instead
arguing that massive slow rotators grow hierarchically in tandem with their
host clusters.
