Comparison of 13CO Line and Far-Infrared Continuum Emission as a Diagnostic of Dust and Molecular Gas Physical Conditions: II. The Simulations: Testing the Method

Abstract

The reliability of modeling the far-IR continuum to 13CO J=1-0 spectral line ratios applied to the Orion clouds (Wall 2006) is tested by applying the models to simulated data. The two-component models are found to give the dust-gas temperature difference, $\DT$, to within 1 or 2$ $K. However, other parameters like the column density per velocity interval and the gas density can be wrong by an order of magnitude or more. In particular, the density can be systematically underestimated by an order of magnitude or more. The overall mass of the clouds is estimated correctly to within a few percent. The one-component models estimate the column density per velocity interval and density within factors of 2 or 3, but their estimates of $\DT$ can be wrong by 20$ $K. They also underestimate the mass of the clouds by 40-50%. These results may permit us to reliably constrain estimates of the Orion clouds' physical parameters, based on the real observations of the far-IR continuum and 13CO J=1-0 spectral line. Nevertheless, other systematics must be treated first. These include the effects of background/foreground subtraction, effects of the HI component of the ISM, and others. These will be discussed in a future paper (Wall 2006a).