Large-scale bulk flows from the Cosmicflows-2 catalogue

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Oxford Academic


The Cosmicflows-2 catalogue is a compendium of peculiar velocity measurements. While it has many objects in common with the COMPOSITE catalogue, a previously analysed collection of peculiar velocity data found to give an unexpectedly large bulk flow on large scales, the data in Cosmicflows-2 have been reanalysed to ensure consistency between distances measured using different methods. In particular, a focus on accurate distances led the authors of the Cosmicflows-2 to not correct for homogeneous or inhomogeneous Malmquist bias, both or which are corrected for in the COMPOSITE compilation. We find remarkable agreement between the COMPOSITE and the Cosmicflows-2 if the small EFAR sample of clusters located in two dense superclusters is removed from both surveys, giving results that are inconsistent with the Λ cold dark matter standard model with Planck central parameters at the 98 per cent level. On smaller scales we find overall agreement between data sets and consistency with the standard model.





Richard Watkins, Hume A. Feldman; Large-scale bulk flows from the Cosmicflows-2 catalogue, Monthly Notices of the Royal Astronomical Society, Volume 447, Issue 1, 11 February 2015, Pages 132–139,