We investigate the [ O ii ] emission-line as a star formation rate ( SFR ) indicator using integrated spectra of 97 galaxies from the Nearby Field Galaxies Survey ( NFGS ) .
The sample includes all Hubble types and contains SFRs ranging from 0.01 to 100 { M } _ { \odot } yr ^ { -1 } .
We compare the Kennicutt [ O ii ] and H \alpha SFR calibrations and show that there are two significant effects which produce disagreement between SFR ( [ O ii ] ) and SFR ( H \alpha ) : reddening and metallicity .
Differences in the ionization state of the ISM do not contribute significantly to the observed difference between SFR ( [ O ii ] ) and SFR ( H \alpha ) for the NFGS galaxies with metallicities \log ( { O / H } ) +12 \gtrsim 8.5 .
The Kennicutt [ O ii ] –SFR relation assumes a typical reddening for nearby galaxies ; in practice , the reddening differs significantly from sample to sample .
We derive a new SFR ( [ O ii ] ) calibration which does not contain a reddening assumption .
Our new SFR ( [ O ii ] ) calibration also provides an optional correction for metallicity .
Our SFRs derived from [ O ii ] agree with those derived from H \alpha to within 0.03-0.05 dex .
We show that the reddening , E ( B - V ) , increases with intrinsic ( i.e .
reddening corrected ) [ O ii ] luminosity for the NFGS sample .
We apply our SFR ( [ O ii ] ) calibration with metallicity correction to two samples : high-redshift 0.8 < z < 1.6 galaxies from the NICMOS H \alpha survey , and 0.5 < z < 1.1 galaxies from the Canada-France Redshift Survey .
The SFR ( [ O ii ] ) and SFR ( H \alpha ) for these samples agree to within the scatter observed for the NFGS sample , indicating that our SFR ( [ O ii ] ) relation can be applied to both local and high- z galaxies .
Finally , we apply our SFR ( [ O ii ] ) to estimates of the cosmic star formation history .
After reddening and metallicity corrections , the star formation rate densities derived from [ O ii ] and H \alpha agree to within \sim 30 % .