A PROTOCLUSTER AT z=2.45

International audienceWe present the spectroscopic confirmation of a z = 2.45 protocluster. Its member galaxies lie within a radius of 1.4 Mpc (physical) on the sky and within Delta v +/- 700 km s(-1) along the line of sight. We estimate an overdensity of 10, suggesting that the structure has made the turnaround but is not assembled yet. A comparison to the Millennium simulation suggests that analogous structures evolve into 10(14)-10(15) M-circle dot h(-1) type dark matter halos by z = 0, qualifying the notion of “protocluster.” The search for the complete census of mock progenitor galaxies at z similar to 2.5 of these massive z = 0 mock clusters reveals that they are widely spread over areas with a diameter of 3-20 Mpc. This suggests that the optical selection of such protoclusters can result in a rich diversity regarding their z = 0 descendants. We also searched for signs of environmental differentiation in this protocluster. While we see a weak trend for more massive and more quiescent galaxies within the protocluster, this is not statistically significant