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1999AJ....117.2102I - Astron. J., 117, 2102-2140 (1999/May-0)
High-latitude radio emission in a sample of edge-on spiral galaxies.
IRWIN J.A., ENGLISH J. and SORATHIA B.
Abstract (from CDS):
We find that all but one galaxy show evidence for nonthermal high-latitude radio continuum emission, suggesting that cosmic-ray (CR) halos are common in star-forming galaxies. Of these, eight galaxies are new detections. The high-latitude emission is seen over a variety of spatial scales and in discrete and/or smooth features. In some cases, discrete features are seen on large scales, suggesting that smooth radio halos may consist, in part, of discrete features combined with low spatial resolution. In general, the discrete features emanate from the disk, but estimates of CR diffusion lengths suggest that diffusion alone is insufficient to transport the particles to the high latitudes seen (>15 kpc in one case). Thus CRs likely diffuse through low-density regions and/or are assisted by other mechanisms (e.g., winds).
We searched for correlations between the prevalence of high-latitude radio emission and a number of other properties, including the global SFR, supernova input rate per unit star-forming area, E{dot}A, and environment, and do not find clear correlations with any of these properties. A subset of the data allows, at best, for only a weak correlation with E{dot}A. Our one nondetection (NGC 4517), however, occurs at a threshold level consistent with that found by Dahlem, Lisenfeld, & Golla. The lack of a good correlation with star formation indicators could be the result of the different timescales for star formation processes compared with the duration of the radio emission. Correlations with other properties, such as environment, are more difficult to assess. However, a few isolated galaxies display strong radio halos, indicating that an interaction is not necessary to produce the extraplanar emission.
Abstract Copyright: ∼
Journal keyword(s): ISM: Cosmic Rays - Galaxies: Halos - Galaxies: Spiral - Radio Continuum
Simbad objects: 18
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