EVOLVING GRAVITATIONALLY UNSTABLE DISKS OVER COSMIC TIME: IMPLICATIONS FOR THICK DISK FORMATION

Observations of disk galaxies at z similar to 2 have demonstrated that turbulence driven by gravitational instability can dominate the energetics of the disk. We present a one-dimensional simulation code, which we have made publicly available, that economically evolves these galaxies from z similar to 2 to z similar to 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 similar to 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.