The 6dF Galaxy Survey: bulk flows on 50-70 h -1 Mpc scales

Morag I. Scrimgeour, Tamara M. Davis, Chris Blake, Lister Staveley-Smith, Christina Magoulas, Christopher M. Springob, Florian Beutler, Matthew Colless, Andrew Johnson, D. Heath Jones, Jun Koda, John R. Lucey, Yin-Zhe Ma, Jeremy Mould, Gregory B. Poole

Research output: Contribution to journalArticlepeer-review

Abstract

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 70 h−1 Mpc. We investigate and correct for potential bias due to the lognormal velocity uncertainties, and verify our method by constructing Λ cold dark matter (ΛCDM) 6dFGSv mock catalogues incorporating the survey selection function. For a hemisphere of radius 50 h−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 70 h−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 ΛCDM prediction.
Original languageEnglish
JournalMonthly Notices of the Royal Astronomical Society
Early online date2 Nov 2015
DOIs
Publication statusPublished - 1 Jan 2016

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