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.