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

We use Spitzer 24 mm, 70 mm and ground-based Ha data for a sample of 40 SINGS galaxies to establish a star formation rate (SFR) indicator using 70 mm emission for sub-galactic ([?]0.05-2 kpc) line-emitting regions and to investigate limits in application. A linear correlation between 70 mm and SFR is found and a star formation indicator SFR(70) is proposed for line-emitting sub-galactic regions as S(SFR)(M yr-1 kpc-2 ) = 9.4 x 10-44 S(70)(erg s-1 kpc-2), for regions with 12 + log(O/H) [?] 8.4 and S(SFR) [?] 10-3(M yr-1 kpc-2), with a 1s 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 mm for integrated light from galaxies, we find that there is [?]40% excess 70 mm emission in galaxies, which can be attributed to stellar populations not involved in the current star formation activity.