Interstellar H-alpha emission along the galactic equator

Photographic surveys along the galactic plane, the Palomar Sky Survey red prints, and Fabry-Perot observations have all revealed faint H-alpha emission from the areas between the bright H II regions. The present investigation is concerned with a systematic study of this H-alpha emission. Scans of H-alpha emission were obtained at 2 deg longitude intervals along the galactic equator with a high-throughput Fabry-Perot spectrometer. Much of the H-alpha emission appears to originate from discrete regions which have an electron density of approximately 1-3 per cu cm and which are associated with emission regions visible on photographic surveys. These regions are superposed on a more diffuse H-alpha background which can be accounted for by an rms electron density of approximately 0.1 per cu cm. This H-alpha survey complements radio and photographic data.