The Unusual Abundance of Copper in the Sagittarius Dwarf Spheroidal Galaxy and Implications for the Origin of ω Centauri

Abstract

We present copper abundances for 14 red giant stars in the Sagittarius dwarf spheroidal galaxy (Sgr dSph), showing that [Cu/Fe] is deficient by ~0.5 dex, relative to the Galactic trend. This is most easily understood as due to an enhanced contribution of iron peak nucleosynthesis products from Type Ia supernovae (SNe Ia). The deficient [Cu/Fe] ratios might also be the result of a metallicity-dependent yield from SNe Ia, similar to previous conclusions for Mn, although SN Ia nucleosynthesis predictions suggest a negligible Cu yield. The enhanced SN Ia products, suggested by our low [Cu/Fe] ratios, fit a leaky box chemical evolution scenario for the Sgr dSph, where ejecta from the old, metal-poor, population overwhelmed nucleosynthesis products from younger generations, resulting in young stars with uncharacteristic compositions. The only other system known to have unusually low [Cu/Fe] is the Galactic globular cluster ω Cen, which, like the Sagittarius dwarf galaxy, has strong enhancements of s -process elements. Thus, our copper abundances lend support to the idea that ω Cen is the remaining nucleus of an accreted dwarf galaxy.