DISCOVERY OF A SYNCHROTRON-EMITTING HALO AROUND NGC-253

We present the discovery of a synchrotron-emitting " halo " of relativistic particles and magnetic fields in the inclined spiral galaxy NGC 253. This halo rises to a height of at least 9 kpc. The halo emission is substantially polarized. The spectral index of the radio continuum emission steepens considerably from the disk into the halo. Radio continuum images reveal many "bulges" and "filaments" protruding perpendicular to the plane of NGC 253 along the disk-halo interface, the most prominent of which, the "spur," rises 4 kpc above the plane. We present evidence for outflow from the disk into the halo along this spur, with a velocity greater than 50 km s-1. This outflow appears to be associated with a region of active star formation in the disk.