AAS 202nd Meeting, May 2003
Session 29 Molecular Clouds and the ISM
Poster, Tuesday, May 27, 2003, 10:00am-6:30pm, West Exhbit Hall

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[29.02] Irregular Magnetic Fields and the Linear Polarization of Dust Thermal Emission

D. Wiebe (INASAN, Moscow, Russia), W. D. Watson (UIUC)

We model the polarized dust thermal emission originating in a cloud with both uniform and irregular magnetic field in order to study various factors that may contribute to the polarization hole effect (i. e., a factor of a few decrease in percentage linear polarization as the intensity decreases by an order of magnitude) observed in many, though not in all, dark clouds. Depolarization due to an increase in magnetic field tangling, a density cutoff in the polarizing effect of dust, thermalization, and density-dependent magnetic field are considered. We show that irregularities in the magnetic field can explain some, but not all, of the observed properties of the polarization holes. The anticorrelation of the intensity of dust emission and the percentage of polarization is reproduced better if one assumes that emission by the dust in the densest parts of a turbulent cloud is not polarized. These most dense parts in our models comprise just a few per cent of the entire cloud volume. Thermalization becomes important only for the optical depths of order of a few tens. This work was supported by NSF Grant AST 9988104.

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© 2003. The American Astronomical Soceity.