A multiwavelength view at the heart of the superwind in NGC 253

Although NGC 253 is one of the nearest starburst galaxies, the activity in its central regions is yet to be fully understood. Here we present new optical data from the Hubble Space Telescope of its central region, which reveal numerous discrete sources in a ring-like structure. This is combined with data at infrared, millimetre, radio and X-ray wavelengths to examine the nature of these discrete sources and the nucleus itself. We find that the majority of optical/IR/mm sources are young star clusters that trace out a similar to 50 pc ring that defines the inner edge of a cold gas torus. This reservoir of cold gas has probably been created by gas inflow from a larger scale bar and deposited at the inner Lindblad resonance. The family of compact radio sources lie interior to the starburst ring, and in general do not have optical or IR counterparts. They are mostly supernova remnants. The radio nucleus, which is probably an active galactic nucleus (AGN), lies near the centre of the ring. The X-ray emission from the nuclear source is extended in the ROSAT HRI detector indicating that not all of the X-ray emission can be associated with the AGN. The lack of X-ray variability and the flat radio spectrum of the nucleus, argue against an ultraluminous SN as the dominant energetic source at the galaxy core. The diffuse emission associated with the outflowing superwind is present in the central region on a size scale consistent with the idea of collimation by the gas torus.