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

TL;DR

This study finds unexpected large-scale coherence between galaxy rotation directions and the average motion of their neighbors up to several Mpc, suggesting a possible link to large-scale structure dynamics.

Contribution

It extends previous small-scale coherence studies to larger scales using CALIFA and NSA data, revealing significant dynamical coherence at several Mpc distances.

Findings

Strong evidence of coherence within 1-6 Mpc distances.

Red neighbor galaxies show stronger coherence signals.

Coherence is more pronounced in kinematically well-aligned galaxies.

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 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 (2.8-sigma 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.