Are Elliptical Galaxies Really Metal-Rich?

Original · EN

We review estimates of the metallicities in elliptical galaxies, with an emphasis on recent results from the ASCA satellite. X-ray spectra of elliptical galaxies are adequately fit by models consisting of hot gas with subsolar Fe abundance and roughly solar Si-to-Fe ratio, plus a hard component from an ensemble of X-ray binaries. Although complications in the form of an extra soft continuum or multiple phases can be considered, we show that the consistency of the Si line diagnostic and continuum temperatures demonstrates that the data -- at the present level of sensitivity and spectral resolution -- do not require these. Optical and X-ray Fe abundance estimates are converging, although there are some cases with anomalously low X-ray values. Subsolar elliptical galaxy abundances require serious reconsideration of our preconceptions about elliptical galaxy chemical evolution, intracluster enrichment, and Type Ia supernova rates.