Tracking Warm H_2 in Photodissociation Regions
Abstract
Photodissociation regions (PDRS) include all regions of the interstellar medium in which far-ultraviolet photons play an important role in the chemistry or heating of the gas. These include HI clouds, the surfaces of molecular clouds illuminated by the interstellar radiation field, and molecular clouds illuminated by intense radiation from nearby massive stars. In general, models provide a good match to the observations, but several recent observations of H_2 and CO indicate that models underestimate the gas temperature. We propose to conduct IRS mapping observations of the warm H_2 in several PDRs. The high spatial resolution and sensitivity of Spitzer will allow us to test PDR models and determine if additional sources of heating are required. It is essential to understand the thermal processes in PDRs in order to use PDR models in comparison with data, to derive physical parameters in the ISM of our Galaxy, as well as external galaxies. In addition, we will use our data sets to improve our understanding of PAH emission and PAH emission models. If the broad emission features seen in the near and mid infrared are due to PAHs, then specific band ratios and band widths are predicted to change with local conditions. We use the high spatial resolution of Spitzer along with high sensitivity to create a series of IRS maps to test these models
- Publication:
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Spitzer Proposal
- Pub Date:
- May 2006
- Bibcode:
- 2006sptz.prop30295W