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 fσ ₈ = 0.384 ± 0.052 (stat) ± 0.061 (sys) and our constraint for the redshift-space distortion parameter is β = 0.289+0.044-0.043 (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.