Suppressing star formation in quiescent galaxies with supermassive black hole winds

In order for quiescent galaxies to maintain their low-to-non-existent star formation, there must be a mechanism to remove or heat gas that would otherwise cool to form stars; now supermassive black hole winds that are sufficient to suppress star formation in such galaxies are reported. Red geysers keep a cap on star formation Edmond Cheung et al . describe a previously unrecognized class of galaxy that they call 'red geysers': the prototypical example, Akira, is a quiescent 'red and dead' elliptical galaxy driving an ionized outflowing wind. Quiescent galaxies with little or no ongoing star formation are widespread, their featureless spheroid structure contrasting to the more varied star-forming structures seen in spiral galaxies. Some unknown mechanism must remove or heat gas from stellar mass loss or mergers that would otherwise cool to form stars. Edmond Cheung et al . report the presence of centrally driven winds in typical quiescent galaxies that host low-luminosity active nuclei. These galaxies are surprisingly common, accounting for as much as ten per cent of the population of galaxies of 20 billion solar masses or greater. The authors calculate that, for Akira, the energy input is sufficient to suppress star formation, and suggest that such red geysers may represent how typical quiescent galaxies maintain their quiescence. Quiescent galaxies with little or no ongoing star formation dominate the population of galaxies with masses above 2 × 10 10 times that of the Sun; the number of quiescent galaxies has increased by a factor of about 25 over the past ten billion years (refs 1 , 2 , 3 , 4 ). Once star formation has been shut down, perhaps during the quasar phase of rapid accretion onto a supermassive black hole 5 , 6 , 7 , an unknown mechanism must remove or heat the gas that is subsequently accreted from either stellar mass loss 8 or mergers and that would otherwise cool to form stars 9 , 10 . Energy output from a black hole accreting at a low rate has been proposed 11 , 12 , 13 , but observational evidence for this in the form of expanding hot gas shells is indirect and limited to radio galaxies at the centres of clusters 14 , 15 , which are too rare to explain the vast majority of the quiescent population 16 . Here we report bisymmetric emission features co-aligned with strong ionized-gas velocity gradients from which we infer the presence of centrally driven winds in typical quiescent galaxies that host low-luminosity active nuclei. These galaxi