Is galactic star-formation activity increased during cluster mergers?

We have investigated the effect of pressure from the intracluster medium on disk galaxies in merging clusters. The ram-pressure on the galaxies rapidly increases when two clusters collide. This leads to stripping of the interstellar medium (ISM) and a decrease in the star-formation rate (SFR) of the galaxies. On the other hand, the increase of the SFR caused by compression of the ISM is less significant. Thus, a cluster merger does not trigger, but weakens, the star-formation activity of galaxies. In the central region of colliding clusters, blue galaxies with high velocity should exist, although most galaxies become red. Following a decrease in the blue galaxy fraction in clusters, the fraction of post-starburst galaxies increases. After a merger, many galaxies in the cluster restart star-formation activity and the segregation of blue and red galaxies becomes prominent.