Galaxy Zoo: Evidence for rapid, recent quenching within a population of
  AGN host galaxies
  We present a population study of the star formation history of 1244 Type 2
AGN host galaxies, compared to 6107 inactive galaxies. A Bayesian method is
used to determine individual galaxy star formation histories, which are then
collated to visualise the distribution for quenching and quenched galaxies
within each population. We find evidence for some of the Type 2 AGN host
galaxies having undergone a rapid drop in their star formation rate within the
last 2 Gyr. AGN feedback is therefore important at least for this population of
galaxies. This result is not seen for the quenching and quenched inactive
galaxies whose star formation histories are dominated by the effects of
downsizing at earlier epochs, a secondary effect for the AGN host galaxies. We
show that histories of rapid quenching cannot account fully for the quenching
of all the star formation in a galaxy's lifetime across the population of
quenched AGN host galaxies, and that histories of slower quenching, attributed
to secular (non-violent) evolution, are also key in their evolution. This is in
agreement with recent results showing both merger-driven and non-merger
processes are contributing to the co-evolution of galaxies and supermassive
black holes. The availability of gas in the reservoirs of a galaxy, and its
ability to be replenished, appear to be the key drivers behind this
co-evolution.
