The role of outflows and star formation efficiency in the evolution of early-type cluster galaxies

A phenomenological model for chemical enrichment in early-type galaxies ispresented, in which the process of star formation is reduced to a set of fourparameters: star formation efficiency (Ceff), fraction of ejected gas inoutflows (Bout), formation redshift (zF) and infall timescale (Tf). Out ofthese four parameters, only variations of Bout or Ceff can account for thecolor-magnitude relation. A range of outflows results in a metallicitysequence, whereas a range of star formation efficiencies will yield a mixed age+ metallicity sequence. The age-metallicity degeneracy complicates the issue ofdetermining which mechanism contributes the most (i.e. outflows versusefficiency). However, the determination of the slope of the correlation betweenmass-to-light ratio and mass in clusters at moderate or high redshift willallow us to disentangle age and metallicity