  Observations of disk galaxies at z~2 have demonstrated that turbulence driven
by gravitational instability can dominate the energetics of the disk. We
present a 1D simulation code, which we have made publicly available, that
economically evolves these galaxies from z~2 to z~0 on a single CPU in a matter
of minutes, tracking column density, metallicity, and velocity dispersions of
gaseous and multiple stellar components. We include an H$_2$ regulated star
formation law and the effects of stellar heating by transient spiral structure.
We use this code to demonstrate a possible explanation for the existence of a
thin and thick disk stellar population and the age-velocity dispersion
correlation of stars in the solar neighborhood: the high velocity dispersion of
gas in disks at z~2 decreases along with the cosmological accretion rate, while
at lower redshift, the dynamically colder gas forms the low velocity dispersion
stars of the thin disk.

Astrophysics of Galaxies