AGN lifetimes in UV-selected galaxies: a clue to supermassive black
  hole-host galaxy coevolution
  The coevolution between supermassive black holes (SMBHs) and their host
galaxies has been proposed for more than a decade, albeit with little direct
evidence about black hole accretion activities regulating galaxy star formation
at $z>1$. In this paper, we study the lifetimes of X-ray active galactic nuclei
(AGNs) in $UV$-selected red sequence (RS), blue cloud (BC) and green valley
(GV) galaxies, finding that AGN accretion activities are most prominent in GV
galaxies at $z\sim1.5-2$, compared with RS and BC galaxies. We also compare AGN
accretion timescales with typical color transition timescales of $UV$-selected
galaxies. We find that the lifetime of GV galaxies at $z\sim1.5-2$ is very
close to the typical timescale when the AGNs residing in them stay in the
high-accretion-rate mode at these redshifts; for BC galaxies, the consistency
between the color transition timescale and the black hole strong accretion
lifetime is more likely to happen at lower redshifts ($z<1$). Our results
support the scenario where AGN accretion activities govern $UV$ color
transitions of host galaxies, making galaxies and their central SMBHs coevolve
with each other.
