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

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

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