The stellar populations of early-type galaxies in the Fornax Cluster

We have measured central line strengths for a complete sample of early-type galaxies in the Fornax Cluster comprising 11 elliptical and 11 lenticular galaxies, more luminous than M-B = -17. We find that the centres of Fornax ellipticals follow the locus of galaxies of fixed age in Worthey's models a nd have metallicities varying roughly from half to 2.5 times solar. The cen tres of (relatively low luminosity) lenticular galaxies, however, exhibit a substantial spread to younger luminosity-weighted ages indicating a more e xtended star formation history. Our conclusions are based on two age/metall icity diagnostic diagrams in the Lick/IDS system comprising established ind ices such as [MgFe] and H-beta as well as new and more sensitive indices, s uch as Fe3 and H-gammaA. The inferred difference in the age distribution be tween lenticular and elliptical galaxies is a robust conclusion as the mode ls generate consistent relative ages using different age and metallicity in dicators even though the absolute ages remain uncertain. The absolute age u ncertainty is caused mainly by the effects of non-solar abundance ratios, w hich are not accounted for in the stellar population models. We find that E s are generally overabundant in magnesium and the most luminous galaxies sh ow stronger overabundances. The luminosity-weighted stellar populations of young S0s are consistent with solar abundance ratios or a weak Mg underabun dance. Two of the faintest lenticular galaxies in our sample have blue cont inua and extremely strong Balmer-line absorptions suggesting starbursts <2 Gyr ago.