2 VIEWS OF THE ANDROMEDA GALAXY-H-ALPHA AND FAR-INFRARED

A complete H alpha image of the Andromeda Galaxy (M31) is presented al lowing the first direct measurement of the total H alpha luminosity wh ich is (7.3+/-2.4)x10(6)L.. The H alpha emission is associated with th ree morphologically distinct components; a large scale star-forming ri ng, similar to 1.65 degrees in diameter, contributing 66% of the total H alpha emission, a bright nucleus contributing 6% of the total H alp ha emission with the remaining 28% contributed by a previously unident ified component of extended and filamentary H alpha emission interior to the star forming ring. The correspondence between the H alpha image and the IRAS far-infrared high resolution image is striking when both are convolved to a common resolution of 105 arcsec. The close corresp ondence between the far-infrared and H alpha images suggests a common origin for the two emissions. The star-forming ring contributes 70% of the far-infrared luminosity of M31. Evidence that the ring emission i s energized by high mass stars includes the fact that peaks in the far -infrared emission coincide identically with H II regions in the H alp ha image. In addition, the far-infrared to H alpha luminosity ratio wi thin the star-forming ring is similar to what one would expect for H I I regions powered by stars of spectral types ranging between O9 and B0 . The origin of the filamentary H alpha and far-infrared luminosity in terior to the star-forming ring is less clear, but it is almost certai nly not produced by high mass stars.