Evidence for the connection between star formation rate and the evolutionary phases of quasars

Both theory and observations suggest that outflows driven by an active central supermassive black hole have a feedback effect on shaping the global properties of the host galaxy1–8. However, whether feedback from the outflow is effective, and if so, whether it is positive or negative, have long been controversial. Here, using the latest catalogue from the Sloan Digital Sky Survey, we use the flux ratio of the [O ii] to [Ne v] emission lines as a proxy to compare the star formation rate in the hosts of quasars with different types of broad absorption lines (BALs): low-ionization (Lo)BAL, high-ionization (Hi)BAL and non-BAL. We find that the star formation rate decreases from LoBAL to HiBAL quasars, and then increases from HiBAL to non-BAL quasars. Assuming that the sequence of LoBAL to HiBAL to non-BAL represents evolution, our results are consistent with a quenching and subsequent rebound of star formation in quasar host galaxies. This phenomenon can be explained by suppression of the star formation rate by the outflow and then rebound of the rate once the outflow disappears as the quasars evolve from HiBALs to non-BALs. Our result suggests that the quasar outflow has a negative global feedback on galaxy evolution. Through an analysis of broad absorption lines in a range of quasars, quasar outflows are shown to have a negative global feedback effect on star formation, demonstrated by the recovery of star formation rates after the outflows disappear.