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

A complete H alpha image of the Andromeda Galaxy (M31) is presented allowing the first direct measurement of the total H alpha luminosity which is (7.3+/-2.4)x10(6)L.. The H alpha emission is associated with three morphologically distinct components; a large scale star-forming ring, similar to 1.65 degrees in diameter, contributing 66% of the total H alpha emission, a bright nucleus contributing 6% of the total H alpha emission with the remaining 28% contributed by a previously unidentified 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 correspondence 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 is energized by high mass stars includes the fact that peaks in the far-infrared emission coincide identically with H II regions in the H alpha image. In addition, the far-infrared to H alpha luminosity ratio within the star-forming ring is similar to what one would expect for H II regions powered by stars of spectral types ranging between O9 and B0. The origin of the filamentary H alpha and far-infrared luminosity interior to the star-forming ring is less clear, but it is almost certainly not produced by high mass stars.