Linear Tidal Vestige found in the WM Sheet

TL;DR

This study detects a linear tidal influence on galaxy spin orientations within the WM sheet near the Virgo cluster, confirming the linear tidal torque model through observational data and analytic predictions.

Contribution

It provides the first observational evidence linking galaxy spin alignments in the WM sheet to linear tidal effects, validated by analytic modeling.

Findings

Weak, strong, and anti-alignments of galaxy spins with tidal principal directions.

Good quantitative agreement between observed and predicted spin alignments.

Confirmation of linear tidal torque influence in large-scale structure.

Abstract

We present a vestige of the linear tidal influence on the spin orientations of the constituent galaxies of the WM sheet discovered in the vicinity of the Virgo cluster and the Local Void. The WM sheet is chosen as an optimal target since it has a rectangular parallelepiped-like shape whose three sides are in parallel with the supergalactic Cartesian axes. Determining three probability density functions of the absolute values of the supergalactic Cartesian components of the spin vectors of the WM sheet galaxies, we investigate their alignments with the principal directions of the surrounding large-scale tidal field. When the WM sheet galaxies located in the central region within the distance of $2\,h^{-1}$Mpc are excluded, the spin vectors of the remaining WM sheet galaxies are found to be weakly aligned, strongly aligned, and strongly anti-aligned with the minor, intermediate and major principal directions of the surrounding large-scale tidal field, respectively. To examine whether or not the origin of the observed alignment tendency from the WM sheet is the linear tidal effect, we infer the eigenvalues of the linear tidal tensor from the axial ratios of the WM sheet with the help of the Zel'dovich approximation and conduct a full analytic evaluation of the prediction of the linear tidal torque model for the three probability density functions. A detailed comparison between the analytical and the observational results reveals a good quantitative agreement not only in the behaviors but also in the amplitudes of the three probability density functions.