### Abstract

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 language | English |
---|---|

Pages (from-to) | 1920-1930 |

Number of pages | 11 |

Journal | Monthly Notices of the Royal Astronomical Society |

Volume | 482 |

Issue number | 2 |

DOIs | |

Publication status | Published - Jan 2019 |

### Cite this

*Monthly Notices of the Royal Astronomical Society*,

*482*(2), 1920-1930. https://doi.org/10.1093/mnras/sty2826

}

*Monthly Notices of the Royal Astronomical Society*, vol. 482, no. 2, pp. 1920-1930. https://doi.org/10.1093/mnras/sty2826

**Bulk flow and shear in the local Universe : 2MTF and COSMICFLOWS-3.** / Qin, Fei; Howlett, Cullan; Staveley-Smith, Lister; Hong, Tao.

Research output: Contribution to journal › Article

TY - JOUR

T1 - Bulk flow and shear in the local Universe

T2 - 2MTF and COSMICFLOWS-3

AU - Qin, Fei

AU - Howlett, Cullan

AU - Staveley-Smith, Lister

AU - Hong, Tao

PY - 2019/1

Y1 - 2019/1

N2 - 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.

AB - 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.

KW - surveys

KW - galaxies: statistics

KW - large-scale structure of Universe

KW - cosmology: observations

KW - H(-1) MPC SCALES

KW - PECULIAR VELOCITY

KW - COSMIC FLOWS

KW - TULLY-FISHER

KW - GALAXIES

KW - QUADRUPOLE

KW - FIELD

U2 - 10.1093/mnras/sty2826

DO - 10.1093/mnras/sty2826

M3 - Article

VL - 482

SP - 1920

EP - 1930

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

SN - 0035-8711

IS - 2

ER -