Spectral index variations of galactic emission

Abstract

We have used all-sky maps at 45 MHz, 408 MHz, 1420 MHz and 22.8 GHz to calculate the distribution of spectral indices across the sky. This requires an adjustment of the adopted zero-levels of the different surveys, which was performed by temperature-versus-temperature (TT) plots. While at high frequencies a spectral steepening with increasing Galactic latitude is seen in the same way as it is observed in nearby galaxies seen edge-on, the spectral index distribution is more complex at lower frequencies. In general there is an agreement with the cooling-convection halo models by Lerche & Schlickeiser (1982), but also local magnetic field variations and variations of the cosmic-ray electron energy spectrum may explain the distribution of low-frequency spectral indices.