A weak lensing study of the Coma cluster

Abstract

Context. Due to observational constraints, dark matter determinations in nearby clusters based on weak lensing are still extremely rare, in spite of their importance for the determination of cluster properties independent of other methods.Aims. We present a weak lensing study of the Coma cluster (redshift∼0.024) based on deep images obtained at the CFHT.Methods. After obtaining photometric redshifts for the galaxies in our field based on deep images in the μ* (1 X 1 deg2), and in the B,V,R and I bands (42'Z 52'), allowing us to eliminate foreground galaxies, we apply weak lensing calculations on shape measurements performed in the μ* image.Results. We derive a map of the mass distribution in Coma, as well as the radial shear profile, and the mass and concentration parameter at various radii. We obtain M200c = 5.1+4.3-2.2X 014h-170M⊙ and .0+3.2-2.5, in good agreement with previous easurements.Conclusions. With deep wide field images it is now possible to analyze nearby clusters with weak lensing techniques, thus opening a broad new field of investigation. © 2009 ESO.