Improving constraints on the growth rate of structure by modelling the density-velocity cross-correlation in the 6dF Galaxy Survey

Abstract

We present the first simultaneous analysis of the galaxy overdensity and peculiar velocity fields by modelling their cross-covariance. We apply our new maximum-likelihood approach to data from the 6-degree Field Galaxy Survey (6dFGS), which has the largest single collection of peculiar velocities to date. We present a full derivation of the analytic expression for the cross-covariance between the galaxy overdensity and peculiar velocity fields and find direct evidence for a non-zero correlation between the fields on scales up to $\sim 50h^{-1}$ Mpc. When utilising the cross-covariance, our measurement of the normalised growth rate of structure is $f{\sigma }_8(z=0)=0.424_{-0.064}^{+0.067}$ (15% precision), and our measurement of the redshift-space distortion parameter is $\beta =0.341_{-0.058}^{+0.062}$ (18% precision). Both measurements improve by $\sim$20% compared to only using the auto-covariance information. This is consistent with the literature on multiple-tracer approaches, as well as Fisher matrix forecasts and previous analyses of 6dFGS. Our measurement of $f{\sigma }_8$ is consistent with the standard cosmological model, and we discuss how our approach can be extended to test alternative models of gravity.

v2: 20 pages, 10 figures, 3 tables. Figure 10 and text updated to include additional references

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• The Redshift-Space Momentum Power Spectrum I: Optimal Estimation From Peculiar Velocity Surveys
• Constraining the curvature density parameter in cosmology
• A local measurement of the growth rate from peculiar velocities and galaxy clustering correlations in the 6dF Galaxy Survey
• Complementarity of Peculiar Velocity Surveys and Redshift Space Distortions for Testing Gravity
• DESI Peculiar Velocity Survey -- Fundamental Plane
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• Testing Gravity Using Type Ia Supernovae Discovered by Next-Generation Wide-Field Imaging Surveys
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