Detection of the Vorticity Effect on the Disk Orientations

TL;DR

This paper provides observational evidence that the vorticity field influences the nonlinear evolution of galaxy angular momentum, showing strong alignments between galaxy spins and local vorticity in different cosmic web environments.

Contribution

It introduces a method to measure vorticity from galaxy surveys and demonstrates its significant role in galaxy spin evolution through observational data.

Findings

Vorticity vectors are anti-aligned with compression directions in knots and filaments.

Galaxy spins are strongly aligned with local vorticity fields.

Null hypothesis of no alignment is rejected at 99.999% confidence.

Abstract

We present an observational evidence for the vorticity effect on the nonlinear evolution of the galaxy angular momentum. We first calculate the vorticity as the curl of the peculiar velocity field reconstructed from the 2MASS redshift survey. Then, measuring the alignments between the vorticity and the tidal shear fields, we study how the alignment strength and tendency depends on the cosmic web environment. It is found that in the knot and filament regions the vorticity vectors are anti-aligned with the directions of the maximal volume compression while in the void and sheet regions they are anti-aligned with the directions of the minimal compression. Determining the spin axes of the nearby large face-on and edge-on disk galaxies from the Seventh Data Release of the Sloan Digital Sky Survey and measuring their correlations with the vorticity vectors at the galaxy positions, we finally detect a clear signal of the alignments between the galaxy spin and the local vorticity fields. The null hypothesis that there is no alignment between them is rejected at the 99.999% confidence level. Our result supports observationally the recently proposed scenario that although the galaxy angular momentum originates from the initial tidal interaction in the linear regime its subsequent evolution is driven primarily by the cosmic vorticity field.