SPITZER 70μm EMISSION AS A STAR FORMATION RATE INDICATOR FOR SUB-GALACTIC REGIONS

We use Spitzer 24 mu m, 70 mu m and ground-based H alpha data for a sample of 40 SINGS galaxies to establish a star formation rate (SFR) indicator using 70 mu m emission for sub-galactic (similar to 0.05-2 kpc) line-emitting regions and to investigate limits in application. A linear correlation between 70 mu m and SFR is found and a star formation indicator SFR(70) is proposed for line-emitting sub-galactic regions as Sigma(SFR) (M(circle dot)yr(-1) kpc(-2)) = 9.4 x 10(-44) Sigma(70) (erg s(-1) kpc(-2)), for regions with 12 + log(O/H) greater than or similar to 8.4 and Sigma(SFR) greater than or similar to 10(-3) (M-circle dot yr(-1) kpc(-2)), with a 1 sigma dispersion around the calibration of similar to 0.16 dex. We also discuss the influence of metallicity on the scatter of the data. Comparing with the SFR indicator at 70 mu m for integrated light from galaxies, we find that there is similar to 40% excess 70 mu m emission in galaxies, which can be attributed to stellar populations not involved in the current star formation activity.