Photometric Properties of Galaxy Population in the Cluster EIS 0048 - 2942 at z ∼ 0 . 64

Deep photometric data in the V-, R-, I-, zand K-bands for the cluster of galaxies EIS 0048-2942 are used to investigate the properties of the galaxy populations at z ∼ 0.64 in a field of 2.5 × 2.5 Mpc. The sample of candidate cluster members (N = 171) is selected by the photometric redshift technique and is complete up to I = 22.5. Galaxies were classified as spheroids and disks according to the shape of the light profile in the I-band, as parametrized by the Sersic index. In both optical and NIR, spheroids define a sharp colour-magnitude sequence, whose slope and zero points are consistent with a high formation redshift (zf > 2). The disk population occupies a different region in the colour-magnitude diagram, having bluer colours with respect to the red sequence. Interestingly, we find some level of mixing between the properties of the two classes: some disks lie on the colour-magnitude sequence or are redder, while some spheroids turn out to be bluer. The spatial distribution of cluster galaxies show a clumpy structure, with a main over-density of radius ∼ 0.5 Mpc, and at least two other clumps distant ∼ 1 Mpc from the center. The various sub-structures are mostly populated by the red galaxies, while the blue population has an almost uniform distribution. The fraction of blue galaxies in EIS 0048-2942 is fB = 0.11 ± 0.07. This is much lower than what expected on the basis of the Butcher-Oemler effect at lower redshifts.