Neutral hydrogen and magnetic fields in M83 observed with the SKA Pathfinder KAT-7

Abstract

We present new KAT-7 observations of the neutral hydrogen (H <scp>i</scp>) spectral line, and polarized radio continuum emission, in the grand-design spiral M83. These observations provide a sensitive probe of the outer-disc structure and kinematics, revealing a vast and massive neutral gas distribution that appears to be tightly coupled to the interaction of the galaxy with the environment. We present a new rotation curve extending out to a radius of 50 kpc. Based on our new H <scp>i</scp> data set and comparison with multiwavelength data from the literature, we consider the impact of mergers on the outer disc and discuss the evolution of M83. We also study the periphery of the H <scp>i</scp> distribution and reveal a sharp edge to the gaseous disc that is consistent with photoionization or ram pressure from the intergalactic medium. The radio continuum emission is not nearly as extended as the H <scp>i</scp> and is restricted to the main optical disc. Despite the relatively low angular resolution, we are able to draw broad conclusions about the large-scale magnetic field topology. We show that the magnetic field of M83 is similar in form to other nearby star-forming galaxies, and suggest that the disc–halo interface may host a large-scale regular magnetic field.