Paper detail

Comparison of the Diffuse Halpha and FUV Continuum Backgrounds: On the Origins of the Diffuse Halpha Background

We compare the diffuse H$α$ map of our Galaxy with the FUV (1370-1710Å) continuum map. The H$α$ intensity correlates well with the FUV intensity. The H$α$/FUV intensity ratio increases in general with the H$α$ intensity and the FUV hardness ratio (1370-1520Å to 1560-1710Å), implying that late OB stars may be the main source of the H$α$ recombination line at high latitudes. The variation of the H$α$ 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 H$α$ and FUV backgrounds but also the radiative transfer mechanisms responsible for the diffuse backgrounds are largely common. Therefore, we propose a scenario wherein the H$α$ background at high latitudes is mostly composed of two components, H$α$ photons produced by in-situ recombination at the ionized regions around late OB stars and dust-scattered light of the H$α$ photons originating from late OB stars.