Photometric properties of galaxy population in the cluster EIS 0048-2942 at z ~ 0.64

¹ Università Federico II, Department of Physics, Napoli, Italy e-mail: labarber@na.astro.it
² I.N.A.F., Istituto Nazionale di Astrofisica Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy e-mail: gianni@na.astro.it
³ I.N.A.F., Istituto Nazionale di Astrofisica Osservatorio Astronomico di Brera, via Brera 28, 20121 Milano, Italy

Corresponding author: P. Merluzzi, merluzzi@na.astro.it

Received: 11 November 2002
Accepted: 9 December 2002

Abstract

Deep photometric data in the V-, R-, I-, z- and K-bands for the cluster of galaxies EIS 0048-2942 are used to investigate the properties of the galaxy populations at in a field of . The sample of candidate cluster members () is selected by the photometric redshift technique and is complete up to . 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 (). 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 shows a clumpy structure, with a main over-density of radius ~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 . This is much lower than what expected on the basis of the Butcher-Oemler effect at lower redshifts.