SITELLE is an 11’x11′ field-of-view imaging Fourier Transform Spectrograph
(iFTS) on CFHT. I will briefly describe the history of iFTS and the
capability of this new, unique, IFU-like instrument. We are carrying out
a program to use SITELLE to study Hα emission in star-forming galaxies
in a sample of z~0.25 galaxy clusters. I will describe a pipeline we have
developed to generate complete samples of cluster emission-line galaxies
(ELGs), and the current data on two clusters, Abell 2390 and Abell 2465.
I will present some initial results from the data, in particular, the
alignment of the difference vectors between emission-line and continuum
light of the ELGs with the direction towards the cluster center, a signature
of ram pressure stripping in operation. The alignment pattern of the offset
vectors in the (velocity-radius) phase space diagram of the cluster is
consistent with a strong ram pressure effect during the first passage
of the galaxies in its in-falling onto the cluster. An analysis of the
star formation rates of these galaxies shows that they are consistent
with ram pressure stripping being a dominant mechanism in the quenching
of star formation in galaxy clusters. I will also show some preliminary
results on the peculiar, strong Hα emission region in the core of the
brightest cluster galaxy in Abell 2390, indicating the occurrence of
a combination of AGN activities and star-formation in the core.