Galactic cosmic ray propagation: self-consistent models for nuclei, electrons and gamma rays

We describe a numerical approach to modelling the diffusive propagation of cosmic-ray nuclei and electrons in the Galaxy. Our main motivation is the interpretation of diffuse Galactic -ray emission. The model addresses both the spatial and energy dependence of the cosmic-ray distribution, uses the observed distributionof interstellar gas and radiation fields, and serves as the basis for predictions of -ray diffuse emission over the energy range 1 MeV 10 GeV, non-thermal radio emission and the directly measured local interstellar electron spectrum. The cosmic-ray nuclear composition data sets tight constraints on the parameters of such models, and we require our models to be in accord with these. Electrons and nuclei are treated in a consistent way in the propagation code. The principal free parameter is the halo scale height, and a range of values 3 10 kpc is considered. For a model with a constant electron injection spectrum it is not possible fit all the data within better than a factor 2. Since the deviations are significant the electron injection spectrum has been adjusted to fulfill better all the constraints set by the observations. This is shown to require a steepening of the injection spectrum by 0.4 in the index around a few GeV, since propagation effects alone cannot produce the required electron spectrum, at least within the confines of this diffusion model. For the model with a break the fit is improved overall, with the exception of -rays above 1 GeV, where too little intensity is predicted and other effects must be invoked. The model with break enables the steepening of the non-thermal radiation spectrum and the interstellar electron spectrum implied by recent studies of solar modulation of electrons to be simultaneously explained. In order to improve predictions of the inverse Compton component, the interstellar radiation field over the Galaxy is recomputed ; this is of particular importance for the far-IR radiation field. Predictions of the high-latitude -ray spectrum including inverse Comptonare presented which are of relevance to the derivation of the isotropic extragalactic component.