  In this study we investigate the relation between stellar mass, dust
extinction and star formation rate (SFR) using ~150,000 star-forming galaxies
from the SDSS DR7. We show that the relation between dust extinction and SFR
changes with stellar mass. For galaxies at the same stellar mass dust
extinction is anti-correlated with the SFR at stellar masses <10^10 M_solar.
There is a sharp transition in the relation at a stellar mass of 10^10 M_solar.
At larger stellar masses dust extinction is positively correlated with the SFR
for galaxies at the same stellar mass. The observed relation between stellar
mass, dust extinction and SFR presented in this study helps to confirm similar
trends observed in the relation between stellar mass, metallicity and SFR. The
relation reported in this study provides important new constraints on the
physical processes governing the chemical evolution of galaxies. The
correlation between SFR and dust extinction for galaxies with stellar masses
>10^10 M_solar is shown to extend to the population of quiescent galaxies
suggesting that the physical processes responsible for the observed relation
between stellar mass, dust extinction and SFR may be related to the processes
leading to the shut down of star formation in galaxies.
