Molecular Clouds as Ensembles of Transient Cores

We construct models of molecular clouds that are considered as ensembles oftransient cores. Each core is assumed to develop in the background gas of thecloud, grow to high density and decay into the background. The chemistry ineach core responds to the dynamical state of the gas and to the gas-dustinteraction. Ices are deposited on the dust grains in the core's dense phase,and this material is returned to the gas as the core expands to low density.The cores of the ensemble number typically one thousand and are placed randomlyin position within the cloud, and are assigned a random evolutionary phase. The models are used to generate molecular line contour maps of a typical darkcloud. These maps are found to represent extremely well the characteristicfeatures of observed maps of the dark cloud L673, which has been observed atboth low and high resolutions. The computed maps are found to exhibit thegeneral morphology of the observed maps, and to generate similar sizes ofemitting regions, molecular column densities, and the separations between peaksof emissions of various molecular species. The models give insight into thenature of molecular clouds and the dynamical processes occurring within them,and significantly constrain dynamical and chemical processes in theinterstellar medium.Comment: 29 pages, 8 figures. Accepted for publication in Ap