Spatially Resolved Ultraviolet, Hα, Infrared, and Radio Star Formation in M81

Abstract

We present Multiband Imaging Photometer for Spitzer (MIPS) observations of\nM81 at 24, 70, and 160 micron. The grand design nature of M81 is clearly seen,\nshowing two well resolved spiral arms containing numerous bright star forming\nregions. The MIPS images reveal a significant amount of cold dust associated\nwith the spiral arms. We investigate the variation of the ultraviolet (UV),\nH-alpha, and infrared (IR) luminosities and star formation rate (SFR)\nindicators across the face of M81 using the MIPS images and archival UV and\nH-alpha images. For regions in M81, we find that UV and H-alpha SFRs\n(uncorrected for dust attenuation) are always lower than the IR SFR. The cause\nof this behavior is dust attenuation and/or using SFR calibrations appropriate\nfor entire galaxies, not regions in galaxies. The characteristics of the dust\nattenuation for the regions indicate the dust grains and/or geometry are\ndifferent from those in starburst galaxies. The behavior of the infrared-radio\ncorrelation in M81 is seen to vary from the global average, with variations\ncorrelated with the morphology of M81.\n