There have been plenty of observational evidence of cluster galaxy evolution such as the Butcher-Oemler effect and the morphology-density relation. However, it has been difficult to identify the responsible physical mechanism for the cluster galaxy evolution. It has been simply difficult to trace the complicated process of galaxy evolution with several giga years of timescale, using the observation which only brings us with information of a single epoch. One of the actively debated candidate mechanisms is the ram-pressure stripping model, where the cold (or hot) galaxy gas is stripped away by the intra-cluster gas, quenching the star-formation in the galaxy. In this letter, we test if the ram-pressure stripping is mainly responsible for the cluster galaxy evolution by investigating velocity dispersion for various sub-samples of cluster galaxies selected using both morphology and color. It is critical to have both morphological and color information since the results based on one of them has been difficult to be interpreted previously.
To this purpose, we have obtained the accurate morphological
information from the HST/ACS and the large number of
spectroscopic cluster member redshifts for 6 galaxy clusters
at 0.83
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