Charting the Chemistry of Galaxies across Cosmic Time

The chemistry of gas and stars in galaxies connects many seemingly disparate areas of astrophysics, from planet formation and stellar evolution to the enrichment and physical state of the circumgalactic and intergalactic media. Because heavy elements are the end product of converting gas to stars, the abundance and distribution of different elements in and around galaxies tells the story of how galaxies grow and change over time. Astronomers have been studying the chemistry of galaxies outside the Milky Way for well over 50 years, but only in the last decade have detailed studies of galaxy enrichment in the distant universe been possible. Using some of the largest spectroscopic galaxy surveys ever assembled, we have made significant advances in the characterization of galaxies that were forming at early times — particularly during “Cosmic Noon,” the period 8-12 Gyr ago when about half of all the stars in the universe were formed. I will discuss how innovative techniques for determining galaxy chemistry have helped to create a more nuanced picture of these young systems and place them in context with what we know about the overall galaxy population and their present-day descendants. These results are well-timed for planning future observations with next-generation facilities like the James Webb Space Telescope, which will allow us to study galaxy evolution during what are still largely unexplored times in cosmic history, including the Epoch of Reionization.