We present an analysis of the stellar populations as a function of mass in a sample of \sim 7000 galaxies of all morphological and emission types from the 6dF Galaxy Survey ( 6dFGS ) .
We measure velocity dispersions and Lick indices from the spectra of the central regions of these galaxies , deriving ages and metallicities from the Lick indices using stellar population models .
We also derive dynamical masses and dynamical mass-to-light ratios for these galaxies by combining the central velocity dispersions with global photometry in the B , R and K bands from SuperCOSMOS and 2MASS .
Together , these data allow us to reduce the degeneracies between age , metallicity and star formation burst-strength that have limited previous studies .

We find that old galaxies exhibit a mass-metallicity relation with logarithmic slope d [ Fe/H ] /dlog M \approx 0.25 , while young galaxies show slopes consistent with zero .
When we account for the effects of the mass-metallicity relation , we obtain a single , consistent relation between mass-to-light ratio and mass for old galaxies in all passbands , M / L \propto M ^ { 0.15 } .
As we have accounted for stellar population effects , this remaining variation in the mass-to-light with mass ( the residual ‘ tilt ’ of the Fundamental Plane ) must have a dynamical origin .
However , we demonstrate that any simple trend between mass-to-light-ratio and mass or luminosity is inconsistent with the observations , and that a more complex relationship must exist .

We find that the central regions of galaxies of all masses often exhibit young stellar populations .
However it is only in the lowest-mass galaxies studied ( \sim 10 ^ { 10 } M _ { \odot } ) that these populations are evident in the global photometry .
In higher-mass galaxies , young central populations have decreasing influence on the global photometry , with there being no discernible impact in galaxies more massive than \sim 2 \times 10 ^ { 11 } M _ { \odot } .
We conclude that the young stellar populations detected in spectroscopic studies are generally centrally concentrated , and that there is an upper limit on the mass of star-forming events in massive galaxies .
These results have important ramifications for mass-to-light ratios estimated from photometric observations .