  We present a novel method to estimate accurate redshifts of star-forming
galaxies by measuring the flux ratio of the same emission line observed through
two adjacent narrow-band filters. We apply this method to our NB912 and new
NB921 data taken with Suprime-Cam on the Subaru Telescope of a galaxy cluster,
XMMXCS J2215.9-1738, at z=1.46 and its surrounding structures. We obtain
redshifts for 170 [OII] emission line galaxies at z~1.46, among which 41
galaxies are spectroscopically confirmed with MOIRCS and FMOS on the Subaru
mainly, showing an accuracy of $\sigma$((z-z_spec})/(1+z_spec))=0.002. This
allows us to reveal filamentary structures that penetrate towards the centre of
the galaxy cluster and intersect with other structures, consistent with the
picture of hierarchical cluster formation. We also find that the projected
celestial distribution does not precisely trace the real distribution of
galaxies, indicating the importance of the three dimensional view of structures
to properly identify and quantify galaxy environments. We investigate the
environmental dependence of galaxy properties with local density, confirming
that the median colour of galaxies becomes redder in higher density region
while the star-formation rate of star-forming galaxies does not depend strongly
on local environment in this structure. This implies that the star-forming
activity in galaxies is truncated on a relatively short time scale in the
cluster centre.
