  The star formation rate in galaxies is well known to correlate with stellar
mass (the `star-forming main sequence'). Here we extend this further to explore
any additional dependence on galaxy surface brightness, a proxy for stellar
mass surface density. We use a large sample of low redshift ($z \leq 0.08$)
galaxies from the GAMA survey which have both SED derived star formation rates
and photometric bulge-disc decompositions, the latter providing measures of
disc surface brightness and disc masses. Using two samples, one of galaxies
fitted by a single component with S\'{e}rsic index below 2 and one of the discs
from two-component fits, we find that once the overall mass dependence of star
formation rate is accounted for, there is no evidence in either sample for a
further dependence on stellar surface density.

Astrophysics of Galaxies