ULTRAVIOLET THROUGH FAR-INFRARED SPATIALLY RESOLVED ANALYSIS OF THE RECENT STAR FORMATION IN M81 (NGC 3031)

The recent star formation (SF) in the early-type spiral galaxy M81 is characterized using imaging observations from the far-ultraviolet to the far-infrared. We compare these data with models of the stellar, gas, and dust emission for subgalactic regions. Our results suggest the existence of a diffuse dust emission not directly linked to the recent star formation. We find a radial decrease of the dust temperature and dust mass density, and in the attenuation of the stellar light. The IR emission in M81 can be modeled with three components: (1) cold dust with a temperature Tch i 18 2 K, concentrated near the H ii regions but also presenting a diffuse distribution; (2) warm dust with Twh i 53 7 K, directly linked with the H ii regions; and (3) aromatic molecules, with diffuse morphology peaking around the H ii regions.We derive several relationships to obtain total IR luminosities from IRmonochromatic fluxes, and we compare five different star formation rate (SFR) estimators for H ii regions in M81 andM51: the UV, H, and three estimators based on Spitzer data. We find that the H luminosity absorbed by dust correlates tightly with the 24 m emission. The correlation with the total IR luminosity is not as good. Important variations from galaxy to galaxy are found when estimating the total SFR with the 24 m or the total IR emission alone. The most reliable es-timations of the total SFRs are obtained by combining the H emission (or the UV) and an IR luminosity (especially the 24 m emission), which probe the unobscured and obscured SF, respectively. For the entire M81 galaxy, abou