by @OCN12 studying the merging cluster A2744. They identified three rare ‘jellyfish’ galaxies located in close proximity to the ICM features associated with a merging subcluster and its shock front. Their interpretation is that the SF knots detected in the tails of stripped gas are due to the rapid increase in pressure experienced by the galaxies interacting with the shock.

Hence, the observations seem to confirm that galaxy/group accretion and cluster-cluster merger affect the cluster galaxies and that the galaxy properties can be sensitive indicators of the merger stage.

Measuring the environmental effects beyond r$_{200}$ {#r200}
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The colour-density relation is observed in galaxy clusters well beyond $r_{200}$ [e.g. @Haines09] and the fraction of star-forming galaxies steadily increases with cluster-centric radius. Nevertheless even at 3-5$\times$ r$_{200}$, the fraction of star-forming galaxies is below that seen in the field [e.g. @CEG11] suggesting that the environment plays a role inducing transformations well outside $r_{200}$.

By means of hydrodynamical cosmological simulations @BMB13 investigated the trend of cold and hot gas contents and SF as function of clustercentric distance in clusters and groups of galaxies. They found a large-scale trend with cold and hot gas contents and SF increasing with the clustercentric distance, but 