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We use the near--infrared Br\gamma hydrogen recombination line as a referencestar formation rate (SFR) indicator to test the validity and establish thecalibration of the {\it Herschel} PACS 70 \mu m emission as a SFR tracer forsub--galactic regions in external galaxies. Br\gamma offers the doubleadvantage of directly tracing ionizing photons and of being relativelyinsensitive to the effects of dust attenuation. For our first experiment, weuse archival CFHT Br\gamma and Ks images of two nearby galaxies: NGC\,5055 andNGC\,6946, which are also part of the {\it Herschel} program KINGFISH (KeyInsights on Nearby Galaxies: a Far-Infrared Survey with Herschel). We use theextinction corrected Br\gamma emission to derive the SFR(70) calibration forH{\sc ii} regions in these two galaxies. A comparison of the SFR(70)calibrations at different spatial scales, from 200 pc to the size of the wholegalaxy, reveals that about 50% of the total 70\mu m emission is due to dustheated by stellar populations that are unrelated to the current star formation.We use a simple model to qualitatively relate the increase of the SFR(70)calibration coefficient with decreasing region size to the star formationtimescale. We provide a calibration for an unbiased SFR indicator that combinesthe observed H\alpha with the 70 \mu m emission, also for use in H{\sc ii}regions. We briefly analyze the PACS 100 and 160 \mu m maps and find thatlonger wavelengths are not as good SFR indicators as 70\mu m, in agreement withprevious results. We find that the calibrations show about 50% differencebetween the two galaxies, possibly due to effects of inclination.

Star Formation Rates in Resolved Galaxies: Calibrations with Near and Far Infrared Data for NGC5055 and NGC6946