Herschel far-IR counterparts of SDSS galaxies: analysis of commonly used star formation rate estimates

We study a hundred of galaxies from the spectroscopic Sloan Digital Sky Survey (SDSS) with individual detections in the far-infrared Herschel Photodetector Array Camera and Spectrometer bands (100 or 160 mu m) and in the GALEX far-ultraviolet band up to z similar to 0.4 in the COSMOS and Lockman Hole fields. The galaxies are divided into four spectral and four morphological types. For the star-forming and unclassifiable galaxies, we calculate dust extinctions from the ultraviolet (UV) slope, the H alpha/H beta ratio and the L-IR/L-UV ratio. There is a tight correlation between the dust extinction and both L-IR and metallicity. We calculate SFRtotal and compare it with other star formation rate (SFR) estimates (H alpha, UV, SDSS) finding very good agreement between them with smaller dispersions than typical SFR uncertainties. We study the effect of mass and metallicity, finding that it is only significant at high masses for SFRH alpha. For the AGN and composite galaxies, we find a tight correlation between SFR and LIR (sigma similar to 0.29), while the dispersion in the SFR-L-UV relation is larger (sigma similar to 0.57). The galaxies follow the prescriptions of the Fundamental Plane in the M-Z-SFR space.