A Correlation between Balmer H α Emission and Infrared Cirrus

A 13×13 image of Balmer Hα emission at galactic latitude -65 is presented. Sensitivity is limited in part by confusion: the peak-to-valley anisotropy of the Hα surface brightness is ∼0.2 Rayleighs on angular scales of 0.1 to 1.0. The morphology of the Hα emission is similar to that of the 100 μm emission previously observed by the Infrared Astronomical Satellite (IRAS). A point-by-point comparison of the two shows a marginally detected (3σ) positive correlation, ρ = +0.14±0.04. The slope of the correlated components of the 100 μm and Hα emissions is 1.26 −0.32 MJy sr −1 R. Using parameters from the literature, we predict that emission from dust and ionized gas at high latitudes produces ∼3 times more Hα emission per unit 100μm emission than does backscattering of Hα emission from Galactic H II regions by dust at high latitude. Observations of this type may allow us to distinguish between Galactic foreground and cosmic background for both the free-free emission and the thermal dust emission associated with the warm ionized medium of the Milky Way.