Suppressing star formation in quiescent galaxies with supermassive black
  hole winds
  Quiescent galaxies with little or no ongoing star formation dominate the
galaxy population above $M_{*}\sim 2 \times 10^{10}~M_{\odot}$, where their
numbers have increased by a factor of $\sim25$ since $z\sim2$. Once star
formation is initially shut down, perhaps during the quasar phase of rapid
accretion onto a supermassive black hole, an unknown mechanism must remove or
heat subsequently accreted gas from stellar mass loss or mergers that would
otherwise cool to form stars. Energy output from a black hole accreting at a
low rate has been proposed, but observational evidence for this in the form of
expanding hot gas shells is indirect and limited to radio galaxies at the
centers of clusters, which are too rare to explain the vast majority of the
quiescent population. 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 galaxies are surprisingly common, accounting for as much
as $10\%$ of the population at $M_* \sim 2 \times 10^{10}~ M_{\odot}$. In a
prototypical example, we calculate that the energy input from the galaxy's
low-level active nucleus is capable of driving the observed wind, which
contains sufficient mechanical energy to heat ambient, cooler gas (also
detected) and thereby suppress star formation.
