Discovery of the X-ray selected galaxy cluster XMMU J0338.8+0021 at z = 1.49 - Indications of a young system with a brightest galaxy in formation

We report the discovery of a galaxy cluster at z = 1.490 originally selected as an extended X-ray source in the XMM-Newton Distant Cluster Project. Further observations carried out with the VLT-FORS2 spectrograph allowed the spectroscopic confirmation of seven secure cluster members, providing a median system redshift of z = 1.490 +/- 0.009. The color-magnitude diagram of XMMU J0338.8+0021 reveals the presence of a well-populated red sequence with z - H approximate to 3, albeit with an apparent significant scatter in color. Since we do not detect indications of any strong star formation activity in these objects, the color spread could represent the different stellar ages of the member galaxies. In addition, we found the brightest cluster galaxy in a very active dynamical state, with an interacting, merging companion located at a physical projected distance of d approximate to 20 kpc. From the X-ray luminosity, we estimate a cluster mass of M-200 similar to 1.2 x 10(14) M-circle dot. The data appear to be consistent with a scenario in which XMMU J0338.8+0021 is a young system, possibly caught in a moment of active ongoing mass assembly.