Joint growth-rate measurements from redshift-space distortions and peculiar velocities in the 6dF Galaxy Survey

We present a new model for the cross-covariance between galaxy redshift-space distortions and peculiar velocities. We combine this with the autocovariance models of both probes in a fully self-consistent, maximum-likelihood method, allowing us to extract enhanced cosmological parameter constraints. When applying our method to the 6-degree Field Galaxy Survey (6dFGS), our constraint on the growth rate of structure is f sigma(8) = 0.384 +/- 0.052(stat) +/- 0.061(sys) and our constraint for the redshift-space distortion parameter is beta = 0.289(-0.043)(+0.044)(stat)+/- 0.049(sys). We find that the statistical uncertainty for the growth rate of structure is reduced by 64 per cent when using the complete covariance model compared to the redshift-space distortion autocovariance model and 50 per cent when compared to using the peculiar-velocity autocovariance model. Our constraints are consistent with those from the literature on combining multiple tracers of large-scale structure, as well as those from other 6dFGS analyses. Our measurement is also consistent with the standard cosmological model.