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

Abstract

We compare the diffuse H$\alpha$ map of our Galaxy with the FUV (1370-1710\AA) continuum map. The H$\alpha$ intensity correlates well with the FUV intensity. The H$\alpha$/FUV intensity ratio increases in general with the H$\alpha$ intensity and the FUV hardness ratio (1370-1520\AA\ to 1560-1710\AA), implying that late OB stars may be the main source of the H$\alpha$ recombination line at high latitudes. The variation of the H$\alpha$ 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$\alpha$ 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$\alpha$ background at high latitudes is mostly composed of two components, H$\alpha$ photons produced by in-situ recombination at the ionized regions around late OB stars and dust-scattered light of the H$\alpha$ photons originating from late OB stars.