Prominent polarized plumes in the galactic center region and their magnetic field

The authors have observed the distribution of linear polarization over the central 2°.5×3°.0 region of the galaxy at 9.05, 9.55, 10.05, and 10.55 GHz. They found that the prominent polarized plumes extend over 1°.6 perpendicular to the galactic plane. Except for these plumes, the authors have detected no remarkable polarized feature within 200 pc of the galactic center. The western side (in galactic coordinates) of the Galactic center lobe (GCL), which was noticed by Sofue and Handa, is thus not polarized, while the eastern side of it agrees with the northern polarized plume and is highly polarized up to 40%. This imples that the emission mechanisms of both sides of the GCL differ from each other, and hence suggests no physical connection between them. In the polarized plumes and the central compact feature, the transverse magnetic field is essentially parallel to the axis of the plumes, and the sign of the rotation measure changes twice: at the northern edge of the northen polarized plume and at a gap between the northern polarized plume and the central compact feature on the radio arc. Faraday rotation is responsible for depolarization, in particular on the central compact polarized feature. The authors propose a model in which the magnetic tube runs perpendicular to the galactic plane at l ≡ 0°.2 and polarization gaps are due to a depolarizing thermal medium which exists within and/or around the tube.