A Uniform History for Galaxy Evolution
  Recent observations indicate a remarkable similarity in the properties of
evolving galaxies at fixed mass and redshift, prompting us to consider the
possibility that most galaxies may evolve with a common history encompassing
star formation, quasar accretion, and eventual quiescence. We quantify this by
defining a "synchronization timescale" for galaxies as a function of mass and
redshift that characterizes the extent to which different galaxies of a common
mass are evolving in the same manner at various cosmic epochs. We measure this
synchronization timescale using 9 different star-forming galaxy observations
from the literature and SDSS quasar observations spanning $0 < z \lesssim 6$.
Surprisingly, this synchronization timescale is a constant, approximately 1.5
Gyr for all combinations of mass and time. We also find that the ratio between
the stellar mass of galaxies turning off star formation and black hole mass of
turnoff quasars is approximately 30:1, much lower than the 500:1 for quiescent
galaxies at low redshift. As a result, we propose a model in which the
star-forming "main sequence", analogous quasar behavior, and other observations
form a galactic evolution "main sequence", in which star formation occurs
earliest, followed by supermassive black hole accretion, and feedback between
the two are dominated by deterministic rather than stochastic processes.
