A Statistical Comparison of Galactic SNRs and Galactic Giant HII Regions
In order to examine the quality of the evidence, we test the hypothesis that all supernovae in the Galaxy lie in narrow spiral arms. The distributions in longitude of 138 SNRs and 100 giant HII regions are presented, and compared with a simple Monte Carlo model in which 140 supernovae are distributed either along arms according to a density wave model, or uniformly in the plane. The model is intended to give a statistical measure of the ratio of Type II (spiral arms) to Type I (disk) supernovae in the Galaxy. We wish to compare the distributions in galactic longitude of supernova remnants (SNRs) with those predicted by our model in order to allow a comparison which is independent of the computed distance to the SNR. The observed SNR distribution seem to correlate with that of the giant HII regions and hence with the spiral arms.
The Monte Carlo model confirms that there is no obvious population of SNRs not confined to spiral arms. This may suggest that the ratio of Type I to Type II events in the Galaxy is less than unity, or that Type I supernovae do not make long-lived extended remnants.
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