On the Origins of the High-Latitude H-alpha Background

Abstract

The diffuse high-latitude H-alpha background is widely believed to be predominantly the result of in-situ recombination of ionized hydrogen in the warm interstellar medium of the Galaxy. Instead, we show that both a substantial fraction of the diffuse high-latitude H-alpha intensity in regions dominated by Galactic cirrus dust and much of the variance in the high-latitude H-alpha background are the result of scattering by interstellar dust of H-alpha photons originating elsewhere in the Galaxy. We provide an empirical relation, which relates the expected scattered H-alpha intensity to the IRAS 100um diffuse background intensity, applicable to about 81% of the entire sky. The assumption commonly made in reductions of CMB observations, namely that the observed all-sky map of diffuse H-alpha light is a suitable template for Galactic free-free foreground emission, is found to be in need of reexamination.

26 pages, 5 figures, Accepted for publication in ApJ

References in corpus (4)

• The Vertical Structure of Warm Ionised Gas in the Milky Way
• Extended Red Emission in High-Galactic Latitude Interstellar Clouds
• Photoionization of High Altitude Gas in a Supernova-Driven Turbulent Interstellar Medium
• Properties of dust and detection of Halpha emission in LDN 1780

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