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 the ISM (excluding particulates) has been found to be closely related to the history of a galaxy’s star formation and can be determined using optical spectroscopic observations of atomic lines, especially bright ones from ionized oxygen and neon. Another pivotal process in setting the metallicity is gas flow both out of the galaxy, driven by supernovae or other processes, and into the galaxy from the intergalactic medium.
Click here for original story, Cosmic galaxy assembly and the evolution of metals
Source: Phys.org