Mass Transport and Turbulence in Gravitationally Unstable Disk Galaxies.
  I: The Case of Pure Self-Gravity
  The role of gravitational instability-driven turbulence in determining the
structure and evolution of disk galaxies, and the extent to which gravity
rather than feedback can explain galaxy properties, remains an open question.
To address it, we present high resolution adaptive mesh refinement simulations
of Milky Way-like isolated disk galaxies, including realistic heating and
cooling rates and a physically motivated prescription for star formation, but
no form of star formation feedback. After an initial transient, our galaxies
reach a state of fully-nonlinear gravitational instability. In this state,
gravity drives turbulence and radial inflow. Despite the lack of feedback, the
gas in our galaxy models shows substantial turbulent velocity dispersions,
indicating that gravitational instability alone may be able to power the
velocity dispersions observed in nearby disk galaxies on 100 pc scales.
Moreover, the rate of mass transport produced by this turbulence approaches
$\sim 1$ $M_\odot$ yr$^{-1}$ for Milky Way-like conditions, sufficient to fully
fuel star formation in the inner disks of galaxies. In a companion paper we add
feedback to our models, and use the comparison between the two cases to
understand what galaxy properties depend sensitively on feedback, and which can
be understood as the product of gravity alone. All of the code, initial
conditions, and simulation data for our model are publicly available.
