Clusters of galaxies are the most massive gravitationally-bound objects in the Universe and the recent discovery of the JKCS041 cluster in the CFHTLS D1 field by Andreon et al (2009) is a crucial piece of observational data for the study of galaxy formation. At a redshift of z=1.9, this makes it the most distant known cluster and a powerful insight into the build-up of structure in the Universe.

Here we show a 3-colour image, comprising imaging from the CFHT Legacy Survey Deep (g and z-band) and from the WIRCam Infra-Red Deep Survey (Ks-band). The cluster members stand out clearly as the highly clustered red (indicating objects bright in the infra-red) galaxies in the center of the image.