The optical properties of galaxies in the Ophiuchus cluster
  We investigate the optical properties of Ophiuchus to obtain clues on the
formation epoch of this cluster, and compare them to those of the Coma cluster,
which is comparable in mass to Ophiuchus but much more disturbed dynamically.
Based on a deep image of the Ophiuchus cluster in the r' band obtained at the
Canada France Hawaii Telescope with the MegaCam camera, we have applied an
iterative process to subtract the contribution of the numerous stars that
pollute the image, due to the low Galactic latitude of the cluster, and
obtained a photometric catalogue of 2818 galaxies fully complete at r'=20.5 mag
and still 91% complete at r'=21.5 mag. We use this catalogue to derive the
cluster Galaxy Luminosity Function (GLF) for the overall image and for a region
(hereafter the "rectangle" region) covering exactly the same physical size as
the region in which the GLF of the Coma cluster was studied by Adami et al.
(2007). We then compute density maps based on an adaptive kernel technique, for
different magnitude limits, and define three circular regions covering 0.08,
0.08 and 0.06 deg^2 respectively centered on the cluster (C), northwest (NW)
and southeast (SE) of the cluster, in which we compute the GLFs. The GLF fits
are much better when a Gaussian is added to the usual Schechter function, to
account for the excess of very bright galaxies. Compared to Coma, Ophiuchus
shows a strong excess of bright galaxies. The properties of the two nearby very
massive clusters Ophiuchus and Coma are quite comparable, though they seem
embedded in different large scale environments. Our interpretation is that
Ophiuchus has built up long ago, as confirmed by its relaxed state (see paper
I) while Coma is still in the process of forming.
