High-Resolution Radio Continuum Observations of Edge-on Spiral Galaxies

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Abstract
Radio continuum emission at 20 cm has been observed in a sample of 16 edge-on galaxies, using the VLA in its A configuration. These galaxies were observed recently at lower resolution by Irwin et al., who found evidence for extraplanar disk-halo features in 15 of the 16 galaxies. Twelve of the galaxies are detected in the new high-resolution observations. Of these, only two, which were previously known Seyferts, show convincing evidence for AGNs. For six of the galaxies, we provide improved positions for the galaxy nuclei. In four galaxies, radio continuum loops extending perpendicular to the major axis have been discovered, confirming previous conclusions from lower resolution observations that extraplanar emission is present, as well as providing further evidence that radio "halos" consist, at least in part, of underlying discrete features. For several galaxies, the resolution is sufficient to reveal individual star-forming regions in the disk. We examine NGC 3556 in detail since this galaxy has been shown by King & Irwin to display extremely large H I supershells. The estimated input energy from supernovae in the brightest radio component of this galaxy is insufficient to drive the observed H I supershells. We explore possible resolutions to this energy deficit.

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