Abstract

As galaxies evolve, they must enrich and exchange gas with the intergalactic medium, but the mechanisms driving these processes remain poorly understood. In this work, we use missing metals as tracers of past gas flows to constrain the history of metal ejection and redistribution in M31. This nearby, roughly L∗ galaxy is a unique case where spatially resolved measurements of the gas-phase and stellar metallicity, dust extinction, and neutral ISM gas content are available, enabling a census of the metal mass present in stars, gas, and dust. We combine spatially resolved star formation histories from the Panchromatic Hubble Andromeda Treasury survey with a model of metal production by Type II SNe, Type Ia SNe, and AGB stars to calculate M31’s metal production history. We find that M31 has lost 62% of its produced metal mass in our fiducial model, and must have experienced metal loss under any model assumptions. We show that the missing metal mass could be harbored in M31’s circumgalactic medium if the majority of these metals reside in a hot gas phase. Finally, we constrain the timing of this metal loss and show that metals produced in the last 1.5 Gyr have been redistributed within the disk.