THE USE OF [Mg/Fe] TO TRACE TRUNCATED STAR FORMATION IN ELLIPTICAL GALAXIESde la Rosa, I.G., de Carvalho, R.R., Vazdekis, A. and Barbuy, B.
The global decay of the Star Formation (SF) rate since redshift 1-2 suggests that an unknown mechanism, probably the merger of galaxies, is quenching the SF. The present work looks for traces of merger action in elliptical galaxies of Hickson Compact Groups (HCG), allegedly being the ideal place for those interactions to occur. By finding evidences of SF truncation in HCGs we would add further clues to the crucial role played by mergers in the global SF rate decay. We study the stellar populations of 22 elliptical galaxies in HCGs and 12 in the field, using three different SSP models and two different emission correction procedures. The [Mg/Fe] abundance ratio has been used to characterize the timescale of the SF history of the galaxies. The galaxies in the field show the "downsizing" behaviour, in which the low-mass members have extended SF histories, with low [Mg/Fe] and high [Z/H]. Contrarily, their counterparts in the HCGs show the opposite behaviour, with high [Mg/Fe] and low [Z/H], indicating that, after entering the dense HCG environment, low-mass field galaxy see their SF truncated, presumably by mergers.