Supercluster A2142 and collapse in action - infalling and merging groups
  and galaxy transformations
  We study the dynamical state and properties of galaxies and groups in the
supercluster SClA2142 that has a collapsing core, to understand its possible
formation and evolution. We find the substructure of galaxy groups using normal
mixture modelling. We have used the projected phase space (PPS) diagram,
spherical collapse model, clustercentric distances, and magnitude gap between
the brightest galaxies in groups to study the dynamical state of groups and to
analyse group and galaxy properties. We compared the alignments of groups and
their brightest galaxies with the supercluster axis. The supercluster core has
a radius of about $8 h^{-1}$Mpc and total mass $M_{\mathrm{tot}} \approx
2.3\times~10^{15}h^{-1}M_\odot$ and is collapsing. Galaxies in groups on the
supercluster axis have older stellar populations than off-axis groups, with
median stellar ages $4 - 6$ and $< 4$Gyr, correspondingly. The cluster A2142
and the group Gr8 both host galaxies with the oldest stellar populations among
groups in SClA2142 having the median stellar age $t > 8$Gyr. Recently quenched
galaxies and active galactic nuclei (AGNs) are mostly located at virial radii
or in merging regions of groups, and at clustercentric distances $D_c \approx 6
h^{-1}$ Mpc. The most elongated groups lie along the supercluster axis and are
aligned with it. Magnitude gaps between the brightest galaxies of groups are
less than one magnitude, suggesting that groups in SClA2142 are dynamically
young. The collapsing core of the supercluster, infall of galaxies and groups,
and possible merging groups, which affect galaxy properties and may trigger the
activity of AGNs, show how the whole supercluster is evolving.
