The advent of deep HST surveys with both the ACS and the WFC3 instrument has opened the way to the detection of the progenitors of early-type galaxies up to z 6. These progenitor objects are found in clusters or proto-clusters selected as red or star-forming overdensities (e.g., Castellano et al. 2007, 2011; Kurk et al. 2009; Papovich et al. 2010; Tanaka et al. 2010; Andreon et al. 2010, 2011; Gobat et al. 2011; Santos et al. 2011; Stanford et al. 2012; Zeinman et al. 2012; Muzzin et al. 2013; Galametz et al. 2014; Mei et al. 2014), and their study is key to the understanding of the first phases of the early-type population formation and evolution. In particular, the most massive ellipticals are predicted to be formed by a fast process at these high redshifts (e.g. Cattaneo et al. 2013). Current scenarios of early-type galaxy formation propose both galaxy mergers and disk accretion. Multiple efforts in both modeling and observations have the goal to discriminate between these two scenario. New observations with KMOS, MUSE and ALMA are expected in 2015 to contribute to this debate. Our GEPI team is involved in surveys with the HST, and their follow-up programs (CANDELS, e.g. Mei et al. 2014; SHARDS; CLASH), and in modeling these progenitor galaxies (Cattaneo et al. 2013).
We organize a workshop March 2015 and invite the main contributors in this field, like Mauro Giavalisco, an expert in the very high redshift Universe, to help with the organization, and to stimulate the discussion around this workshop.