Radial Light Distributions in Five Spiral Galaxies: The Relationship between Young Stars and the Relativistic Gas

The relationship between the young stellar population and the relativistic gas of five spiral galaxies is examined in this paper. The analysis is based on the comparison of azimuthally averaged radial profiles of H alpha emission, red stellar continuum, and radio continuum emission. A direct comparison of the profiles shows that for each galaxy the three light distributions are similar, indicating that all three might be driven by the mass profile of the disk. Radial profiles alone are not useful for correlating the relativistic gas with the stellar populations. A correlation is found, however, between the mass-normalized (normalized by the red stellar continuum profile) H alpha and radio continuum distributions confirming the existence of a relationship between the relativistic gas and Population I stars. It is found that the mass-normalized radio continuum profiles are, on average, broader than the Ha profiles. The breadth of the radio profiles is interpreted to be the result of particle propagation acting to smear out the relativistic gas distribution relative to the source distribution. A technique is developed to obtain quantitative estimates of the scale length of particle propagation. The scales found range from 0.1 to 2 kpc confirming that propagation effects "blur" but do not destroy the signature of the source distribution in the radio data. Our results add further evidence to the hypothesis that the production of relativistic gas in galaxies is associated with the young population of stars.