A study of compact radio sources in nearby face-on spiral galaxies. I. Long-term evolution of M83

We present analyses of deep radio observations of M83 taken with the Very Large Array spanning 15 yr, including never-before-published observations from 1990 and 1998. We report on the evolution of 55 individual point sources, which include four of the six known historical supernovae in this galaxy. A total of 10 sources have X-ray counterparts from a Chandra survey. Each of these sources show nonthermal spectral indices, and most appear to be X-ray supernova remnants. Comparing the radio source list to surveys in the optical and X-ray, we identify three optical/X-ray supernova remnants. Nearly half of the detected radio sources in these observations are coincident with known H II regions lying in the spiral arm structures of the galaxy. We also report on changes in emission from the complex nuclear region, which has shown variability at 20 cm wavelengths. We confirm that the peak radio emission from the nucleus is not coincident with the known optical center. One lesser nuclear peak is consistent with the optical/IR nucleus. Previous dynamical studies of a dark'' nuclear mass indicate a possible match to other radio nuclear emission regions in M83.