Comparison of the diffuse Hα and FUV continuum backgrounds: On the origins of the diffuse Hα background

Abstract

We compare the diffuse Hα map of our Galaxy with the FUV (1370-1710 Å) continuum map. The Hα intensity correlates well with the FUV intensity. The Hα/FUV intensity ratio increases in general with the Hα intensity and the FUV hardness ratio (1370-1520 Å to 1560-1710 Å), implying that late OB stars may be the main source of the Hα recombination line at high latitudes. The variation of the Hα 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 Hα and FUV backgrounds but also the radiative transfer mechanisms responsible for the diffuse backgrounds are largely common. Therefore, we propose a scenario wherein the Hα background at high latitudes is mostly composed of two components, Hα photons produced by in situ recombination at the ionized regions around late OB stars and dust-scattered light of the Hα photons originating from late OB stars. © 2011. The American Astronomical Society. All rights reserved.