Mysterious Coherence in Several-Megaparsec Scales Between Galaxy Rotation and Neighbor Motion

In our recent report, observational evidence supports that the rotational direction of a galaxy tends to
be coherent with the average motion of its nearby neighbors within 1 Mpc. We extend the investigation
to neighbors at farther distances, in order to examine if such dynamical coherence is found even in large
scales. The Calar Alto Legacy Integral Field Area (CALIFA) survey data and the NASA-Sloan Atlas
(NSA) catalog are used. From the composite map of velocity distribution of ‘neighbor’ galaxies within
15 Mpc from the CALIFA galaxies, the composite radial profiles of the luminosity-weighted mean
velocity of neighbors are derived. These profiles show unexpectedly strong evidence of the dynamical
coherence between the rotation of the CALIFA galaxies and the average line-of-sight motion of their
neighbors within several Mpc distances. Such a signal is particularly strong when the neighbors are
limited to red ones: the luminosity-weighted mean velocity at 1 < D ≤ 6 Mpc is as large as 30.6±10.9
km s−1
(2.8σ significance to random spin-axis uncertainty) for central rotation (R ≤ Re). In the
comparison of several subsamples, the dynamical coherence tends to be marginally stronger for the
diffuse or kinematically-well-aligned CALIFA galaxies. For this mysterious coherence in large scales,
we cautiously suggest a scenario that it results from a possible relationship between the long-term
motion of a large-scale structure and the rotations of galaxies in it.

posted Aug 31, 2019, 4:21 PM by Shifu RC

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