Left: RM variations along the azimuthal angle in the inner ring between 0.5 kpc and 2 kpc radius in the plane of the galaxy, based on the robust 0 data at 15″ × 12″ resolution presented in this paper (blue curve), compared with the previous 6 cm/13 cm data at 11″ resolution from Han et al. (1999) (red curve). Data points are shown with the estimated error bars of each ring. Solid lines show fourth-order polynomial functions. Right: RM variations along the azimuthal angle in the ring between 4 kpc and 10 kpc radius in the plane of the galaxy derived from the robust 2 data at 32″ × 26″ resolution of this paper (blue curve) and from the previous 6 cm/13 cm data at 25″ resolution from Han et al. (1999) (red curve).