A Chandra Survey of Early-Type Galaxies. I. Metal Enrichment in the Interstellar Medium

We present a Chandra study of the emission-weighted metal abundances in 28 early-type galaxies, spanning ~3 orders of magnitude in X-ray luminosity (L_X). We report constraints for Fe, O, Ne, Mg, Si, S, and Ni. We find no evidence of the very subsolar Fe abundance (Z_Fe) historically reported, confirming a trend in recent observations of bright galaxies and groups, nor do we find any correlation between Z_Fe and luminosity. Excepting one case, the ISM is single-phase, indicating that multitemperature fits found with ASCA reflected temperature gradients that we resolve with Chandra. We find no evidence that Z_Fe (ISM) is substantially lower than the stellar metallicity estimated from simple stellar population models. In general, these quantities are similar, which is inconsistent with galactic wind models and recent hierarchical chemical enrichment simulations. Our abundance ratio constraints imply that 66%+/-11% of the ISM Fe was produced in SNe Ia, similar to the solar neighborhood, indicating similar enrichment histories for elliptical galaxies and the Milky Way. Although these values are sensitive to the considerable systematic uncertainty in the supernova yields, they are in agreement with observations of more massive systems. This indicates considerable homology in the enrichment process operating from cluster scales to low-to-intermediate-L_X galaxies. The data uniformly exhibit low Z_O/Z_Mg ratios, which have been reported in some clusters, groups, and galaxies. This is inconsistent with standard SN II metal yield calculations and may indicate an additional source of enrichment, such as Population III hypernovae.