The Hα and infrared star formation rates for the nearby field galaxy survey

We investigate the Ha and infrared star formation rate (SFR) diagnostics for galaxies in the Nearby Field Galaxy Survey (NFGS). For the 81 galaxies in our sample, we derive Hα fluxes (included here) from integrated spectra. There is a strong correlation between the ratio of far-infrared to optical luminosities L(FIR)/ L(Hα) and the extinction E(B- V) measured with the Balmer decrement. Before reddening correction, the SFR(IR) and SFR(Hα) are related to each other by a power law: SFR(IR) = (2.7 ± 0.3)SFR(Hα)^1.30±0.06. Correction of the SFR(Hα) for extinction using the Balmer decrement and a classical reddening curve both reduces the scatter in the SFR(IR)-SFR(Hα) correlation and results in a much closer agreement between the two SFR indicators; SFR(IR) = (0.91 ± 0.04)SFR(Hα_corr)^1.07±0.03(IR) and SFR(Hα) agree to ∼10%. This SFR relationship spans 4 orders of magnitude and holds for all Hubble types with IRAS detections in the NFGS. A constant ratio between the SFR(IR) and SFR(Hα) for all Hubble types, including early types (S0-Sab), suggests that the IR emission in all these objects results from a young stellar population.