Distant Clusters (EDisCS)

 We take part in the ESO Distant Cluster Survey (EDisCS), a large project on 20 fields with clusters at z=0.4-1. Using VLT deep imaging and spectroscopy, ACS/HST imaging and other data from space observatories, like XMM and Spitzer, we want to trace the evolution of cluster galaxies and clusters between z=1 and the present epoch, covering 1/2 the age of the Universe. EDisCS is unique for the wide mass range of its clusters, compared to other high-z cluster surveys that include only exceptionally massive clusters, whose local counterpart are extremely rare. EDisCS clusters thus represent the progenitors of 'typical clusters' today.

Among the fundamental aims of this project there is understanding the origin of the Hubble sequence and the star formation history of a galaxy. In order to link galaxy evolution with the evolution of the parent structure, we have studied cluster velocity dispersions from spectroscopy and masses from lensing, as well as cluster X-ray emission. Highlights on galaxy evolution concern the red galaxies, the star forming galaxies as seen in Halpha and optical emission lines, visual and automated galaxy morphologies, galaxy luminosity functions and mass functions, star formation histories of galaxies in our clusters, groups and the field, the assembly of Brightest Cluster Galaxies and the metallicities of passive and active galaxies.

 Some recent highlights: more massive early-type galaxies have formed their stars and have assembled at very high redshifts, while less massive galaxies on average continue to form stars and evolve over longer timescale; edics3 edics3 there is a correlation between the ratio of star-forming galaxies and the cluster velocity dispersion. We have assessed how this fraction evolves to z=0, pointing at the importance of the cluster mass growth history; for the first time, we show how the fraction of star-forming galaxies and the average star formation rate depend on local galaxy density in distant clusters (left figure), finding the fraction is independent from the density while the average star formation shows a possible peak at intermediate densities; the star formation-density and the morphology-density relation are fully equivalent at these redshifts, at odds with low-z results (right figure); the incidence of post-starburst galaxies strongly depends on environment at z=0.4 to 0.8, with higher frequency in the most massive clusters and in those groups with few star-forming galaxies, suggesting these latter environments must be efficient at truncating star formation too. Ongoing work on Ediscs data will tell us about the IR side of star formation obscured by dust and about the mass assembly of galaxies as a function of galaxy mass and history.

People: B.M. Poggianti, J. Fritz, B. Vulcani

Collaboration: S. White (MPA-Garching, D) A. Aragon-Salamanca (Nottingham, UK) P. Best (ROE, Scotland) D. Clowe (Ohio Univ., USA) J. Dalcanton (U.Washington, USA) G. De Lucia (MPA, D) C. Halliday (OA, I) P. Jablonka (Geneve, CH) B. Milvang-Jensen (Copenhagen, DK) R. Pello (OMP, F) G. Rudnick (NOAO, USA) R. Saglia (Munich, D) L. Simard (U. Victoria, C) A. von der Linden (MPA-Garching, D) D. Zaritsky (Arizona Univ., USA)

Recent Publications: Poggianti et al. (2009),   ApJ in press; Poggianti et al. (2008), ApJ, 684,888; Milvang-Jensen et al. (2008), A&A, 482,419; Whiley et al. (2008), MNRAS, 387,1253; Desai et al. (2007), ApJ, 660,1151; De Lucia et al. (2007), MNRAS, 374,809