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Description
Statistically complete samples comprising 33 bright spiral galaxies that are strong radio sources were selected. Sixteen of the galaxies have integrated radio-to-optical flux ratios greater than 10 times the median value for normal spirals. The remainder contain radio cores <=20" in size and stronger than 90mJy at 1415MHz or 60mJy at 2695MHz. High-resolution (2" at 1413MHz or 0.6" at 4885MHz) maps of these galaxies were made with the Very Large Array. The radio sources are usually confined to the central 1kpc of the galaxies, lying within and extending parallel to their stellar disks. There is no evidence for ejection from central components. Most of the sources appear to be coextensive with regions of intense star formation (bolometric luminosities ~10^10-10^11L_{Sun}). The typical radio luminosity, ~10^21^W/Hz/sr at 1413MHz, of the resolved sources can be explained by synchrotron radiation from supernova remnants (SNRs) produced at the rate of ~1/yr. Five of the radio sources are <=1pc in size and probably are not related to star formation or SNRs. The radio and 10-{mu}m flux densities of the extended sources are roughly proportional. The bolometric mass-to luminosity ratios in some active regions are too low to have been maintained for a Hubble time. Nearly all of the strong, extended radio sources are found in galaxies with nearby companions, so most of the episodic bursts of star formation are apparently triggered by galaxy-galaxy interactions.
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