The Active Assembly of the Virgo Cluster: Indications for Recent Group
  Infall From Early-Type Dwarf Galaxies
  Virgo is a dynamically young galaxy cluster with substructure in its spatial
and kinematic distribution. Here, we simultaneously study the phase-space
distribution and the main characteristics of Virgo's galaxies, particularly its
most abundant galaxy population - the early-type dwarfs - to understand their
environmental transformation histories. Aside from known correlations with
morphological types - like the larger average clustercentric distance of
late-type galaxies - we find an intriguing behavior of early types with
magnitudes -17 >= M_r >= -18. They show a large velocity spread and an
asymmetric phase-space distribution, similar to the late-type galaxies and
different from the early types just one magnitude brighter/fainter.
Furthermore, we find a close phase-space aggregation of early-type dwarfs at
large clustercentric distance and high relative velocity. Nearly all of them
show signatures of disk components and their colors imply stellar ages that are
younger than the population average. They are not located closely together but
spread azimuthally around the cluster center. We show that this is expected
from simulations of an infalling galaxy group that slowly gets dispersed after
its first pericentric passage. We thus conclude that these galaxies are recent
arrivals, and that the peculiar phase-space distribution of early-type dwarfs
is evidence for the ongoing growth of this galaxy population. Studying galaxies
based on their phase space correlations is a unique way to compare the
properties of recent and older cluster members, and to understand which
environment most influenced their present-day characteristics.
