Young Massive Star Clusters as Cosmic Abundance Probes

Studying a galaxy's present-day chemical abundances provides information on its star-forming history. Cosmological simulations of galaxy evolution make predictions about the relative metal contents of galaxies as a function of their stellar mass, a trend known as the mass-metallicity relation. These predictions can be tested with observations of nearby galaxies.  However, providing reliable, accurate abundance measurements at extragalactic distances is extremely challenging.  Our team has developed a technique to extract abundance information from individual red supergiant (RSG) stars at megaparsec distances, using KMOS as the workhorse instrument. We have expanded this project to study young massive star clusters containing dozens of RSGs, which allows us to study galaxies at even larger distances. This has ultimately allowed us to construct a mass-metallicity relation for nearby galaxies, which I will present here.