Colour-magnitude relation, Butcher-Oemler effect, X-ray and weak lensing mass estimates.

We present results from the multi-wavelength study of XMMU J1230.3+1339 at z�1. We analyze deep multi-band wide-field images from the Large Bin ocular Telescope, multi-object spectroscopy observations from VLT, as well as space-based serendipitous observations, from the GALEX and Chandra X-ray observatories. We apply a Bayesian photometric redshift code to derive the redshifts using the FUV, NUV and the deep U, B, V, r, i, z data. We make further use of spectroscopic data from FORS2 to calibrate our photometric redshifts, and investigate the photometric and spectral properties of the early-type galaxies. We achieve an accuracy of4 z= (1 + z) = 0.07 (0.04) and the fraction of catastrophic outliers is �= 13 (0) %, when using all (secure) spectroscopic data, respectively. The i− z against z colour-magnitude relation of the photo-z members shows a tight red-sequence with a zero point of 0.935 mag, and slope equal to -0.027. We observe evidence for a truncation at the faint end of the red-cluster-sequence and the Butcher-Oemler effect, finding a fraction of blue galaxies fb � 0.5. Further we conduct a weak lensing analysis of the deep 26 0 �26 0 r-bandLBC image. The observed shear is fitted with a Single-Isothermal-Spher e and a Navarro-Frenk-White model to obtain the velocity dispersion and the model parameters, respectively. Our best � � �� −