Key points are not available for this paper at this time.
Sixteen out of a statistically complete sample of 33 bright spiral galaxies that are strong radio sources have integrated radio-to-optical flux ratios greater than ten times the median value for normal spirals, and the remainder contain radio cores that are less than 20 arcsec in size and stronger than 90 mJy at 1415 MHz or 60 mJy at 2695 MHz. Most of the sources appear to be coextensive with regions of intense star formation, and their typical radio luminosity can be explained by synchrotron radiation from supernova remnants produced at the rate of less than about 1/yr. Because nearly all of the strong, extended radio sources are found in galaxies with nearby companions, most of the episodic bursts of star formation are apparently triggered by galaxy-galaxy interactions.
Condon et al. (Fri,) studied this question.