New constraints on red-spiral galaxies from their kinematics in clusters
  of galaxies
  The distributions of the pairwise line-of-sight velocity between galaxies and
their host clusters are segregated according to the galaxy's colour and
morphology. We investigate the velocity distribution of red-spiral galaxies,
which represents a rare population within galaxy clusters. We find that the
probability distribution function of the pairwise line-of-sight velocity
$v_{\rm{los}}$ between red-spiral galaxies and galaxy clusters has a dip at
$v_{\rm{los}} = 0$, which is a very odd feature, at 93\% confidence level. To
understand its origin, we construct a model of the phase space distribution of
galaxies surrounding galaxy clusters in three-dimensional space by using
cosmological $N$-body simulations. We adopt a two component model that consists
of the infall component, which corresponds to galaxies that are now falling
into galaxy clusters, and the splashback component, which corresponds to
galaxies that are on their first (or more) orbit after falling into galaxy
clusters. We find that we can reproduce the distribution of the line-of-sight
velocity of red-spiral galaxies with the dip with a very simple assumption that
red-spiral galaxies reside predominantly in the infall component, regardless of
the choice of the functional form of their spatial distribution. Our results
constrain the quenching timescale of red-spiral galaxies to a few Gyrs, and the
radius where the morphological transformation is effective as $r \sim 0.2
h^{-1} \rm{Mpc}$.
