Rejuvenation triggers nuclear activity in nearby galaxies
  Feedback, in particular from active galactic nuclei (AGN), is believed to
play a crucial role in the evolution of galaxies. In the local Universe, many
galaxies with an AGN are indeed observed to reside in the so-called green
valley, usually interpreted as a transition phase from a blue star-forming to a
red quenched state. We use data from the Sloan Digital Sky Survey to show that
such an interpretation requires substantial revision. Optically-selected nearby
AGN galaxies follow exponentially declining star formation histories, as normal
galaxies of similar stellar and dark matter halo mass, reaching in the recent
past ($\sim$0.1 Gyr ago) star formation rate levels consistent with a quiescent
population. However, we find that local AGN galaxies have experienced a sudden
increase in their star formation rate, unfolding on timescales similar to those
typical of AGN activity, suggesting that both star formation and AGN activity
were triggered simultaneously. We find that this quenching followed by an
enhancement in the star formation rate is common to AGN galaxies and more
pronounced in early type galaxies. Our results demonstrate that local AGN
galaxies are not just a simple transition type between star-forming and
quiescent galaxies as previously postulated.
