The Star-Forming Molecular Gas in High Redshift Submillimeter Galaxies
  We present a model for the CO molecular line emission from high redshift
Submillimeter Galaxies (SMGs). By combining hydrodynamic simulations of gas
rich galaxy mergers with the polychromatic radiative transfer code, Sunrise,
and the 3D non-LTE molecular line radiative transfer code, Turtlebeach, we show
that if SMGs are typically a transient phase of major mergers, their observed
compact CO spatial extents, broad line widths, and high excitation conditions
(CO SED) are naturally explained. In this sense, SMGs can be understood as
scaled-up analogs to local ULIRGs. We utilize these models to investigate the
usage of CO as an indicator of physical conditions. We find that care must be
taken when applying standard techniques. The usage of CO line widths as a
dynamical mass estimator from SMGs can possibly overestimate the true enclosed
mass by a factor ~1.5-2. At the same time, assumptions of line ratios of unity
from CO J=3-2 (and higher lying lines) to CO (J=1-0) will oftentimes lead to
underestimates of the inferred gas mass. We provide tests for these models by
outlining predictions for experiments which are imminently feasible with the
current generation of bolometer arrays and radio-wave spectrometers.
