A Correlation between Balmer H-alpha Emission and Infrared Cirrus

Abstract

A 13x13 degree image of Balmer H-alpha emission at galactic latitude -65 degrees is presented. Sensitivity is limited in part by confusion: the peak-to-valley anisotropy of the H-alpha surface brightness is 0.2 Rayleighs on angular scales of 0.1 to 1.0 degrees. The morphology of the H-alpha emission is similar to that of the 100 um emission previously observed by the Infrared Astronomical Satellite (IRAS). A point-by-point comparison of the two shows a marginally detected (3-sigma) positive correlation, rho = +0.14 (+-0.04). The slope of the correlated components of the 100 um and H-alpha emissions is 1.26 (+0.45) (-0.32) MJy/sr/R. Using parameters from the literature, we predict that emission from dust and ionized gas at high latitudes produces 3 times more H-alpha emission per unit 100 um emission than does backscattering of H-alpha 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.