The black hole mass metallicity relation and insights into galaxy quenching

One of the most important questions in astrophysics is what causes galaxies to stop forming stars. Previous studies have shown a tight link between quiescence and black hole mass. Other studies have revealed that quiescence is also associated with 'starvation', the halting of gas inflows, which results in the remaining gas being used up rapidly by star formation and in rapid chemical enrichment. In this work we find the final missing link between these two findings. Using a large sample of galaxies, we uncover the intrinsic dependencies of the stellar metallicity on galaxy properties. In the case of the star-forming galaxies, the stellar metallicity is driven by stellar mass. However, for passive galaxies the stellar metallicity is primarily driven by the black hole mass, as traced by velocity dispersion. This result finally reveals the connection between previous studies, where the integrated effect of black hole feedback prevents gas inflows, starving the galaxy, which is seen by the rapid increase in the stellar metallicity, leading to the galaxy becoming passive.