Evidence for spin alignment of spiral and elliptical/S0 galaxies in filaments

TL;DR

This study provides observational evidence that galaxy spin axes are aligned with cosmic filaments, with spirals tending to align parallel and ellipticals perpendicular, supporting tidal torque theory.

Contribution

It offers the first statistically significant observational evidence of galaxy spin-filament alignments using the SDSS survey and a 3D orientation analysis.

Findings

Spiral galaxies tend to have their spin axes parallel to filaments.

Elliptical/S0 galaxies tend to have their spin axes perpendicular to filaments.

The alignment signals are robust across different inclination angle estimates.

Abstract

Galaxies are not distributed randomly in the cosmic web but are instead arranged in filaments and sheets surrounding cosmic voids. Observationally there is still no convincing evidence of a link between the properties of galaxies and their host structures. However, by the tidal torque theory (our understanding of the origin of galaxy angular momentum), such a link should exist. Using the presently largest spectroscopic galaxy redshift survey (SDSS) we study the connection between the spin axes of galaxies and the orientation of their host filaments. We use a three dimensional field of orientations to describe cosmic filaments. To restore the inclination angles of galaxies, we use a 3D photometric model of galaxies that gives these angles more accurately than traditional 2D models. We found evidence that the spin axes of bright spiral galaxies have a weak tendency to be aligned parallel to filaments. For elliptical/S0 galaxies, we have a statistically significant result that their spin axes are aligned preferentially perpendicular to the host filaments; we show that this signal practically does not depend on the accuracy of the estimated inclination angles for elliptical/S0 galaxies.