Cosmic galaxy assembly and the evolution of metals

Astronomers refer to all the elements heavier than helium as "metals," even elements that are typically found in gaseous form. In the big bang only hydrogen and helium (and a trace of lithium) were created while the "metals" were all made subsequently in stellar processes. The abundance of metals in the interstellar medium (ISM) of galaxies--the metallicity of the galaxies--thus quantifies the collective stellar processes that govern galactic evolution. The metallicity of the gaseous phase of th...