Abstract
The effect of a newly born star cluster inside a giant molecular cloud (GMC) is to produce a hot bubble and a thin, dense shell of interstellar gas and dust swept up by the H II expansion, strong stellar winds, and repeated supernova explosions. Lying at the inner side of the shell is the photodissociation region (PDR), the origin of much of the far-infrared/submillimeter/millimeter (FIR/submm/mm) radiation from the interstellar medium (ISM). We present a model for the expanding shell at different stages of its expansion that predict mm/submm and far-IR emission line intensities from a series of key molecular and atomic constituents in the shell. The kinematic properties of the swept-up shell predicted by our model are in very good agreement with the measurements of the supershell detected in the nearby starburst galaxy M82. We compare the modeling results with the ratio-ratio plots of the FIR/submm/mm line emission in the central 1.0 kpc region to investigate the mechanism of star-forming activity in M82. Our model has yielded appropriate gas densities, temperatures, and structure scales compared to those measured in M82, and the total H2 content is compatible with the observations. This implies that the neutral ISM of the central star-forming region is a product of fragments of the evolving shells.
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