The case against bimodal star formation in elliptical galaxies

We consider the present-day photometric and chemical properties of ellipticalgalaxies, adopting the bimodal star formation scenario of Elbaz, Arnaud &Vangioni-Flam (1995). These models utilise an initial mass function (IMF)biased heavily toward massive stars during the early phases of galacticevolution, leading to early Type II supernovae-driven galactic winds. Asubsequent lengthy, milder, star formation phase with a normal IMF ensues,responsible supposedly for the stellar population observed today. Based uponchemical evolution arguments alone, this scenario has been invoked to explainthe observed metal mass, and their abundance ratios, in the intracluster mediumof galaxy clusters. Building upon the recent compilations ofmetallicity-dependent isochrones for simple stellar populations, we haveconstructed a coupled photometric and chemical evolution package for compositestellar populations in order to quantify the effects of such a model upon thephoto-chemical properties of the resultant elliptical galaxies. We demonstratethat these predicted properties are incompatible with those observed at thecurrent epoch.Comment: 11 pages of uuencoded compressed PostScript. Accepted for publication in MNRA