The 6dF Galaxy Survey: Bulk Flows on 50-70 h⁻¹ Mpc scales

الأصل · EN

We measure the bulk flow of the local Universe using the 6dF Galaxy Survey peculiar velocity sample (6dFGSv), the largest and most homogeneous peculiar velocity sample to date. 6dFGSv is a Fundamental Plane sample of 10⁴ peculiar velocities covering the whole southern hemisphere for galactic latitude |b| > 10∘, out to redshift z=0.0537. We apply the `Minimum Variance' bulk flow weighting method, which allows us to make a robust measurement of the bulk flow on scales of 50 and 70h⁻¹ Mpc. We investigate and correct for potential bias due to the lognormal velocity uncertainties, and verify our method by constructing Λ CDM 6dFGSv mock catalogues incorporating the survey selection function. For a hemisphere of radius 50h⁻¹ Mpc we find a bulk flow amplitude of U=248±58 km s⁻¹ in the direction (l,b) = (318∘±20∘,40∘±13∘), and for 70h⁻¹ Mpc we find U=243±58 km s⁻¹, in the same direction. Our measurement gives us a constraint on σ₈ of 1.01⁺¹.⁰⁷₋₀.₅₈. Our results are in agreement with other recent measurements of the direction of the bulk flow, and our measured amplitude is consistent with a Λ CDM prediction.