Ambipolar Diffusion and Far-Infrared Polarization from the Galactic Circumnuclear Disk

We describe an implicit prediction of the accretion disk models constructed by Wardle and Königl (1990) for the circumnuclear disk (CND) of gas and dust near the Galactic center: supersonic ambipolar diffusion, an essential dynamical ingredient of the Wardle-Königl disks, will cause the alignment of dust grains due to a process described by Roberge, Hanany, & Messinger (1995). We calculate synthetic maps of the polarized thermal emission which would be caused by ambipolar alignment in the preferred Wardle-Königl model. Our maps are in reasonable agreement with 100μm polarimetry of the CND if we assume that the grains have shapes similar to those of grains in nearby molecular clouds and that the CND contains a disordered magnetic field in energy equipartition with its ordered field. Subject headings: dust — Galaxy: center — infrared: ISM: continuum — ISM: magnetic fields — MHD — polarization