The G Dwarf Problem Exists in Other Galaxies

Stellar population models with abundance distributions determined from theanalytic Simple model of chemical evolution fail to match observations of thenuclei of bulge-dominated galaxies in three respects. First, the spectralenergy distribution in the mid-ultraviolet range 2000 < lam < 2400 exceedsobservation by ~ 0.6 mag. Most of that excess is due to metal-poor mainsequence stars. Second, the models do not reproduce metal-sensitive opticalabsorption features that arise mainly from red giant stars. Third, the strengthof a Ca II index sensitive to hot stars does not jibe with the predicted numberof A-type horizontal branch stars. The number of metal poor stars in galaxiesis at least a factor of two less than predicted by the Simple model, exactlysimilar to the ``G Dwarf problem'' in the solar cylinder. Observations atlarger radii in local group galaxies indicate that the paucity of metal poorstars applies globally, rather than only in the nuclei. Because of thedominance of metal rich stars, primordial galaxies will have a plentiful dustsupply early in their star formation history, and thus will probably have weakLyman-alpha emission, as is apparently observed. We confirm that early-typegalaxies cannot have been formed exclusively from mergers of small all-stellarsubsystems, a result already established by dynamical simulations. Theconstraint of peaked abundance distributions will limit future chemicalevolution models. It will also make age estimates for the stellar populationsin early type galaxies and bulges more secure.