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Centro de Astrofísica da Universidade do Porto

On the galaxy luminosity function in the central regions of the Coma cluster.

A. Biviano, F. Durret, D. Gerbal, O. Le Fèvre, C. Lobo, A. Mazure, E. Slezak

We have obtained new redshifts for 265 objects in the central 48x25 arcmin2 region of the Coma cluster. When supplemented with literature data, our redshift sample is 95% complete up to a magnitude b26.5=18.0 (the magnitudes are taken from the photometric sample of Godwin et al. 1983). Using redshift-confirmed membership for 205 galaxies, and the location in the colour-magnitude diagram for another 91 galaxies, we have built a sample of cluster members which is complete up to b26.5=20.0. We show that the Coma cluster luminosity function cannot be adequately fitted by a single Schechter (1976) function, because of a dip in the magnitude distribution at b26.5~17. The superposition of an Erlang (or a Gauss) and a Schechter function provides a significantly better fit. We compare the luminosity function of Coma to those of other clusters, and of the field. Luminosity functions for rich clusters look similar, with a maximum at Mb=~-19.5+5xlog h50, while the Virgo and the field luminosity functions show a nearly monotonic behaviour. These differences may be produced by physical processes related to the environment which affect the luminosities of a certain class of cluster galaxies.

Astronomy and Astrophysics
Volume 297, Page 610
May 1995

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