THE ORIGIN OF THE FAR-INFRARED LUMINOSITY WITHIN THE SPIRAL GALAXY M101

High resolution 60 and 100 mu m images obtained with the Infrared Astr onomical Satellite (IRAS) are compared with Ha images in order to inve stigate the origin of the far-infrared luminosity within the late-type spiral galaxy M101. There is a good correspondence between the far-in frared and Hac morphology. The far-infrared and Her luminosities have been measured at 129 independent locations on the star forming disk of M101. After correcting the Her luminosity for extinction and extrapol ating the IRAS (40-120 mu m) luminosity to 1000 mu m we find that the far-infrared luminosity is commensurate with that expected from the O and B stars which are required to ionize the hydrogen gas, at all loca tions within M101. Additionally, the IRAS HiRes 60 and 100 mu m images reveal that the dust temperature peaks coincide identically with the location of H ii regions. The far-infrared luminosity of M101 is radia ted primarily by dust with temperatures well in excess of that expecte d for cirrus, but similar to that observed for Galactic and extragalac tic H II regions.