On the Composition and Distribution of Dust in Galactic H II Regions
Abstract
The dust emission and distribution from two Galactic H II regions, the Rosette Nebula and the lambda Orionis H II region, have been modeled and compared with spatially resolved IRAS observations. The grain models used in this study are consistent with observations of isolated interstellar grains. The wealth of published observations of these two H II regions was used to constrain the free parameters in the infrared emission models. In this respect, the models presented in this thesis represent a comprehensive, multi-wavelength study of each H II region. Despite their regular appearance, the distribution in both regions has significant deviations from spherical symmetry. In particular, the IR emission for the lambda Orionis H II region requires nonspherical distribution near the central core. Within both H II regions, the I_ nu(60)/I_nu(100) ratio is not representative of a single grain temperature. Either strong temperature fluctuations in small (50 to 200 A) grains or "astronomical" iron grains could be responsible for the strength of the 60 μm emission. Also, significant depletion is required of the grains that give rise to both the 12 and 25 μm emission in the diffuse ISM. The smallest grains are found to be severely depleted in radiation fields of 20 to 36 times UV component of the diffuse ISRF.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1994
- Bibcode:
- 1994PhDT........51S
- Keywords:
-
- ROSETTE NEBULA;
- INTERSTELLAR DUST;
- LAMBDA ORIONIS;
- Physics: Astronomy and Astrophysics