Wobbling galaxy spin axes in dense environments

TL;DR

This study examines how galaxy spin axes change in dense cluster environments, revealing that mergers and tidal forces can significantly alter spin vectors, but overall, spin alignments are largely preserved over time.

Contribution

It provides new insights into the mechanisms affecting galaxy spin vectors in clusters, highlighting the roles of mergers and tidal perturbations in dense environments.

Findings

Larger angular changes occur in galaxies with lower initial rotational support.

Mergers and close tidal encounters cause significant spin vector swings.

Most satellite galaxies experience minimal spin change after infall.

Abstract

The orientation of galaxy spin vectors within the large scale structure has been considered an important test of our understanding of structure formation. We investigate the angular changes of galaxy spin vectors in clusters - denser environments than are normally focused upon, using hydrodynamic zoomed simulations of 17 clusters YZiCS and a set of complementary controlled simulations. The magnitude by which galaxies change their spin vector is found to be a function of their rotational support with larger cumulative angular changes of spin vectors when they have initially lower $V_{\theta}/\sigma$. We find that both mergers and tidal perturbations can significantly swing spin vectors, with larger changes in spin vector for smaller pericentre distances. Strong tidal perturbations are also correlated with the changes in stellar mass and specific angular momentum of satellite galaxies. However, changes in spin vector can often result in a canceling out of previous changes. As a result, the integrated angular change is always much larger than the angular change measured at any instant. Also, overall the majority of satellite galaxies do not undergo mergers or sufficiently strong tidal perturbation after infall into clusters, and thus they end up suffering little change to their spin vectors. Taken as a whole, these results suggest that any signatures of spin alignment from the large scale structure will be preserved in the cluster environment for many gigayears.