COMPARISON OF THE DIFFUSE H alpha AND FUV CONTINUUM BACKGROUNDS: ON THE ORIGINS OF THE DIFFUSE H alpha BACKGROUND

Abstract

We compare the diffuse Ha map of our Galaxy with the FUV (1370-1710 angstrom) continuum map. The Ha intensity correlates well with the FUV intensity. The H alpha/FUV intensity ratio increases in general with the Ha intensity and the FUV hardness ratio (1370-1520 angstrom to 1560-1710 angstrom), implying that late OB stars may be the main source of the Ha recombination line at high latitudes. The variation of the Ha intensity as a function of the Galactic latitude is also very similar to that of the FUV intensity. The results likely suggest that not only the original radiation sources of the Ha and FUV backgrounds but also the radiative transfer mechanisms responsible for the diffuse backgrounds are largely common. Therefore, we propose a scenario wherein the Ha background at high latitudes is mostly composed of two components, Ha photons produced by in situ recombination at the ionized regions around late OB stars and dust-scattered light of the Ha photons originating from late OB stars.