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

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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 -0.58 +1.07. 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
Pages (from-to)386-401
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Early online date2 Nov 2015
Publication statusPublished - 1 Jan 2016


  • astro-ph.CO
  • surveys
  • glaxies: kinematics and dynamics
  • galaxies: statistics
  • cosmology: observations
  • large-scale structure of Universe


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