Polarimetric imaging of the Galactic center at 12.4 microns - The detailed magnetic field structure in the northern arm and the east-west bar

Recent closely sampled imaging polarimetry of the central 0.5 pc of the Galaxy at 12.4 microns with a 58 x 62 array camera system is presented. The results clearly show that the magnetic field is a property of the diffuse material of the large-scale structures in Sgr A (the northern arm and east-west bar) rather than the embedded sources. The magnetic field is independent of the changes of density and temperature in the compact source environments. The magnetic field direction in much of the east-west bar is complex, and its polarization is probably the result of the superposition of differently oriented filaments. The abrupt decrease of polarization southwest of IRS 1 observed previously is confirmed and shown to reverse sign. This is due either to a rapid change of magnetic field direction close to the dynamical center, or to the superposition of nearly orthogonal fields. The field direction changes smoothly across IRS 1, and no discontinuity of motion here is found.