The integrated metallicity profile of the Milky Way

Abstract

The heavy element abundance profiles of galaxies place stringent constraints on galaxy growth and assembly history. As the Milky Way is currently the only spiral galaxy in which we can measure temporally resolved chemical abundances, it enables insights into the origin of metallicity gradients and their correlation with the growth history of galaxies. However, until now, these abundance profiles have not been translated into the integrated-light measurements that are needed to compare the Milky Way with the general galaxy population. Here we report the measurement of the light-weighted, integrated stellar metallicity profile of our Galaxy. We find that the integrated stellar metallicity profile of the Milky Way has a ∧-like broken shape, with a mildly positive gradient inside a Galactocentric radius of 7 kpc and a steep negative gradient outside. This broken integrated metallicity profile of the Milky Way is not unique but is not common among Milky Way-mass star-forming galaxies observed in the MaNGA survey and simulated in the TNG50 cosmological simulation. Our results suggest that the Milky Way might not have a typical metallicity distribution for a galaxy of its mass, and thus offers valuable insight into the rich variety of galaxy enrichment processes.