Thermally Dominated Carbon Monoxide Emission in the Taurus Molecular Cloud Complex

We analyze the structure of a region of the Taurus molecular cloud containing star-forming dense cores, as traced by emission from the J \ 1¨0 rotational transition of the carbon monoxide isotopomer, C18O. While the spatial structure of the velocity-integrated emission is rather featureless, there is sub- stantial structure in the emission integrated over small velocity widths, and the entire three-dimensional data set (right ascension, declination, and velocity) can be broken into a collection of nearly discrete components. We construct a cloud model consisting of nine individual Gaussian components and —nd that the data are best replicated when these components have sizes of D0.1 pc and velocity dispersions comparable to or smaller than the thermal velocity dispersion of molecular hydrogen at a temperature of 10 K. We —nd that nearly all of the molecular mass of the cloud is contained within these quiescent structures. At least two of the structures are detected in observations in the J \ 4¨3 line of these HC 3 N; two structures are likely associated with the two forming stars in the region. Our results suggest that thermally dominated structures may be common in regions containing dense cores, but that many of these structures are insufficiently dense to be detected with dense gas tracers. Subject headings: ISM: cloudsISM: individual (Taurus Molecular Cloud) ¨ ISM: molecules ¨ radio lines: ISM