Astronomy & Astrophysics

Free access article

Issue		A&A Volume 399, Number 3, March I 2003
Page(s)		899 - 911
Section		Galactic structure and dynamics
DOI		10.1051/0004-6361:20021829

A&A 399, 899-911 (2003)
DOI: 10.1051/0004-6361:20021829

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

F. La Barbera¹, P. Merluzzi², A. Iovino³, M. Massarotti² and G. Busarello²

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

(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 ${z\sim0.64}$ in a field of $\mathrm{2.5\times 2.5~Mpc^2}$ . 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 ( ${z_{\rm f} > 2}$ ). 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 shows 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 $f_B=0.11 \pm 0.07$ . This is much lower than what expected on the basis of the Butcher-Oemler effect at lower redshifts.

Key words: galaxies: clusters: individual: EIS 0048-2942 -- galaxies: evolution -- galaxies: fundamental parameters -- galaxies: photometry

Offprint request: P. Merluzzi, merluzzi@na.astro.it

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