Bulk flow and shear in the local Universe: 2MTF and COSMICFLOWS-3

Fei Qin, Cullan Howlett, Lister Staveley-Smith, Tao Hong

Research output: Contribution to journalArticle

5 Citations (Scopus)


The low-order kinematic moments of galaxies, namely bulk flow and shear, enables us to test whether theoretical models can accurately describe the evolution of the mass density field in the nearby Universe. We use the so-called eta MLE maximum likelihood estimator in log-distance space to measure thesemoments from a combined sample of the 2MASS Tully-Fisher (2MTF) survey and the COSMICFLOWS-3 (CF3) compilation. Galaxies common between 2MTF and CF3 demonstrate a small zero-point difference of -0.016 +/- 0.002 dex. We test the eta MLE on 16 mock 2MTF survey catalogues in order to explore how well the eta MLE recovers the true moments, and the effect of sample anisotropy. On the scale size of 37 h(-1) Mpc, we find that the bulk flow of the local Universe is 259 +/- 15 km s(-1) in the direction is (l, b) = (300 +/- 4 degrees, 23 +/- 3.) (Galactic coordinates). The average shear amplitude is 1.7 +/- 0.4 h km s(-1) Mpc(-1). We use a variable window function to explore the bulk and shear moments as a function of depth. In all cases, the measurements are consistent with the predictions of the Lambda cold dark matter (Lambda CDM) model.

Original languageEnglish
Pages (from-to)1920-1930
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Publication statusPublished - Jan 2019

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