Mysterious Coherence in Several-megaparsec Scales between Galaxy Rotation and Neighbor Motion

Abstract

Abstract 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-megaparsec 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 ≤ R e ). 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 in which it results from a possible relationship between the long-term motion of a large-scale structure and the rotations of galaxies in it.