Dusty star-forming galaxies in the red sequence: the cluster Abell 901/902 seen with COMBO-17

It is well-established that clusters are dominated by red galaxies wirh old stellar populations, while the field population consists mostly of blue galaxies with younger stars. The origin of this relation may be due to 'nature' or 'nurture'. In the nurture scenario the transformation from blue to red could be due to a variety of processes. However, we only start to discover the smoking gun of this transformation today. The medium-band filter set of COMBO-17 has made a new discovery possible by chance, which I will present here. In an outlook I will discuss, how these data and follow-up with HST and Spitzer may hold clues as to what is going on in cluster accretion. There is also a unique and strong case for investigating clusters found in the ALHAMBRA survey.