* Astronomy

Title: Cl 1103.7-1245 at z=0.96: the highest redshift galaxy cluster in the EDisCS survey
Authors: Benedetta Vulcani (1,2), Alfonso Aragón-Salamanca (3), Bianca M. Poggianti (2), Bo Milvang-Jensen (4), Anja von der Linden (5), Jacopo Fritz (6), Pascale Jablonka (7,8), Olivia Johnson (9), Dennis Zaritsky (10) ((1) Astronomical Department, Padova University, Padova, Italy, (2) INAF-Astronomical Observatory of Padova, Padova, Italy, (3) School of Physics and Astronomy, University of Nottingham, Nottingham, UK, (4) Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark, (5) Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Stanford, CA, USA, (6) Sterrenkundig Observatorium Vakgroep Fysica en Sterrenkunde Universeit Gent, Gent, Belgium, (7) Observatoire de Genéve, Laboratoire d'Astrophysique Ecole Polytechnique Federale de Lausanne (EPFL), Sauverny, Switzerland, (8) GEPI, Observatoire de Paris, Université Paris Diderot, Meudon Cedex, France (9) Royal Observatory, Greenwich, UK, (10) Steward Observatory, University of Arizona, Tucson, AZ, USA)

We present new spectroscopic observations in a field containing the highest redshift cluster of the ESO Distant Cluster Survey (EDisCS). We measure galaxy redshifts and determine the velocity dispersions of the galaxy structures located in this field. Together with the main cluster Cl1103.7-1245 (z=0.9580; sigma_{clus} = 522 ±111 km/s) we find a secondary structure at z=0.9830, Cl1103.7-1245c. We then characterise the galaxy properties in both systems, and find that they contain very different galaxy populations. The cluster Cl1103.7-1245 hosts a mixture of passive elliptical galaxies and star-forming spirals and irregulars. In the secondary structure Cl1103.7-1245c all galaxies are lower-mass star-forming irregulars and peculiars. In addition, we compare the galaxy populations in the Cl1103.7-1245 z=0.9580 cluster with those in lower redshift EDisCS clusters with similar velocity dispersions. We find that the properties of the galaxies in Cl1103.7-1245 follow the evolutionary trends found at lower redshifts: the number of cluster members increases with time in line with the expected growth in cluster mass, and the fraction of passive early-type galaxies increases with time while star-forming late types become less dominant. Finally, we find that the mean stellar masses are similar in all clusters, suggesting that massive cluster galaxies were already present at z~1.

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