Morphologies and stellar populations of galaxies in the core of Abell 2218

We present a study of the stellar populations and morphologies of galaxies in the core of the galaxy cluster Abell 2218. Integral field spectroscopy (IFS) observations were performed using PMAS in the PPAK mode covering a field of view of similar to 74 x 64 arcsec(2) centred on the core of the cluster, in order to obtain spectroscopy of an unbiased flux-limited sample of cluster galaxies. 43 objects were detected in the IFS data, 31 of them with enough signal-to-noise ratio to derive the redshift, all of them brighter than I The morphologically segregated colour-magnitude diagram shows that the early-type galaxies cover the range of brighter and redder colours (the so-called 'red sequence'). A large fraction of spiral galaxies (similar to 50 per cent) is found, most of them fainter than the limit of previous studies. They cover a wide range in colours, from blue colours typical of Butcher-Oemler galaxies to red colours similar to those of early-type galaxies. This result indicates that early-type galaxies are more massive and have older stellar populations, while late-type galaxies are less massive and have a wider range of stellar populations. The distribution of luminosity-weighted ages as a function of metallicities and luminosity-weighted masses, and the distribution of Sersic indices as a function of the luminosity-weighted masses confirm these results. They in fact agree with a proposed two-step scenario for the evolution of galaxies in clusters, where the star formation is quenched first in the infalling spirals, after which a morphological transformation follows that requires larger time-scales. This scenario naturally explains the population faint late-type galaxies with old stellar populations observed in this cluster. In addition, an extremely blue merging galaxy system is found at the core, with the nominal redshift of the cluster.