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