[O ii ] Emission in Quasar Host Galaxies: Evidence for a Suppressed Star Formation Efficiency

Abstract

We investigate the [OII] 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 Msun/yr. We compare the Kennicutt [OII] and H-alpha SFR calibrations and show that there are two significant effects which produce disagreement between SFR[OII] 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([OII]) and SFR(H-alpha) for the NFGS galaxies with metallicities log(O/H)12>8.5. The Kennicutt [OII]-SFR relation assumes a typical reddening for nearby galaxies; in practice, the reddening differs significantly from sample to sample. We derive a new SFR([OII]) calibration which does not contain a reddening assumption. Our new SFR([OII]) calibration also provides an optional correction for metallicity. Our SFRs derived from [OII] agree with those derived from H-alpha to within 0.03-0.05 dex. We apply our SFR([OII]) calibration with metallicity correction to two samples: high-redshift 0.8