Star formation rate indicators in the Sloan Digital Sky Survey

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  • 30 June 2003
Abstract
(Abridged) The SDSS DR1 provides a database of ~106000 unique galaxies in the main galaxy sample with measured spectra, of which 3079 have 1.4 GHz luminosities from FIRST. A sample of star-forming (SF) galaxies are identified from among those with radio detections, using optical spectral diagnostic diagrams. By using 1.4 GHz luminosities as a star formation rate (SFR) estimate insensitive to obscuration effects, the SFRs derived from the measured SDSS H-alpha, [OII] and u-band luminosities are compared to the radio estimates of SFR. It is established that straightforward corrections for obscuration and aperture effects reliably bring the SDSS emission line and photometric SFR estimates into agreement with those at 1.4 GHz, although considerable scatter (~60%) remains in the relations. It thus appears feasible to perform detailed investigations of star formation for large and varied samples of star-forming (SF) galaxies, by utilising the available spectroscopic and photometric measurements from the SDSS. We provide exact prescriptions for determining the SFR for SDSS galaxies. The expected strong correlation between [OII] and H-alpha line fluxes for SF galaxies is seen, but with a median line flux ratio F_[OII]/F_H-alpha=0.23, about a factor of two smaller than that found in the sample of Kennicutt (1992). This correlation, consistent with the luminosity-dependent relation found by Jansen et al (2001), is used to derive an updated calibration for the [OII] derived SFRs that is found to be highly consistent with those derived from 1.4 GHz and H-alpha luminosities. The median obscuration for the SDSS SF systems is found to be A_H-alpha=1.2 mag, somewhat higher than the 1 mag commonly assumed. For the radio detected sample the median obscuration is notably higher, 1.6 mag, and with a broader distribution.

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