AAS 205th Meeting, 9-13 January 2005
Session 117 Star Formation, Embedded Young Stars and Their Disks
Oral, Wednesday, January 12, 2005, 10:00-11:30am, Golden Ballroom

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[117.02] From the H II Region to the Molecular Cloud: Determining Physical Conditions in Star Forming Regions

N. P. Abel (University of Kentucky)

Infrared missions such as Spitzer offer new insights into the chemical evolution and star formation history of the universe. Although objects such as starburst galaxies, which are among the most luminous objects in the universe, are the primary focus, OMC-1, a lower luminosity region with superb spatial resolution, serves as a benchmark to test the physics of newly formed O stars interacting with the surrounding molecular environment. The classical approach in determining conditions in the ionized, photodissociated, and molecular regions is to treat each problem separately. In actuality, however, this is a single continuous phenomenon, linked through the transport of gas and radiation.

Here we self-consistently calculate the physical conditions and emission from the hot HII region to the cold, molecular gas as a continuous hydrostatic layer. The ion states of the first 30 elements, along with the abundances of ~70 molecules, are determined with the temperature and electron density. The grain physics is treated self-consistently, with grain charge transfer, single photon heating, and PAH effects all included. Additionally, level populations of all the rotational/vibrational levels of the ground electronic state of molecular hydrogen are determined (see the dissertation talk of Gargi Shaw).

As a benchmark, we consider the physical conditions through OMC-1 ~1 west of the Trapezium, where emission-line observations of the HII region and the PDR/molecular cloud all exist. Accurately interpreting this spectrum will give us confidence that we can apply our calculations to more luminous and distant starburst galaxies. We predict the sometimes significant contribution of the HII region to important PDR emission-line diagnostics. This has consequences for the interpretation of IR observations, the deduced values of n(H) and G0 in PDRs, and hence the overall conditions in star forming regions. All calculations were developed with the spectral synthesis code Cloudy, which is publicly available at www.nublado.org.


The author(s) of this abstract have provided an email address for comments about the abstract: npabel2@uky.edu

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