  Galaxies change their properties as they assemble into clusters. In order to
understand the physics behind that, we need to go back in time and observe
directly what is occurring in galaxies as they fall into a cluster. We have
conducted a narrow-band and $J$-band imaging survey on a cluster CL1604-D at
$z=0.923$ using a new infrared instrument SWIMS installed at the Subaru
Telescope. The narrow-band filter, NB1261, matches to H$\alpha$ emission from
the cluster at $z=0.923$. Combined with a wide range of existing data from
various surveys, we have investigated galaxy properties in and around this
cluster in great detail. We have identified 27 H$\alpha$ emitters associated
with the cluster. They have significant overlap with MIPS 24$\mu$m sources and
are located exclusively in the star forming regime on the rest-frame $UVJ$
diagram. We have identified two groups of galaxies near the cluster in the 2D
spatial distribution and the phase-space diagram, which are likely to be
in-falling to the cluster main body. We have compared various physical
properties of star forming galaxies, such as specific star formation rates
(burstiness) and morphologies (merger) as a function of environment; cluster
center, older group, younger group, and the field. As a result, a global
picture has emerged on how the galaxy properties are altered as they assemble
into a denser region. This includes the occurrence of mergers, enhancement of
star formation activity, excursion to the dusty starburst phase, and eventual
quenching to a passive phase.
