Tidally induced bars of galaxies in clusters

TL;DR

This study uses N-body simulations to show that tidal forces in galaxy clusters can induce bar formation in disk galaxies, with stronger and earlier bars forming on tighter orbits, influencing galaxy morphology distribution within clusters.

Contribution

It demonstrates that tidal interactions in clusters can trigger bar formation, providing a detailed analysis of how orbit and tidal strength affect bar properties and galaxy evolution.

Findings

Bars form soon after first pericenter passage in all orbits.

Stronger, longer, and slower bars develop on tighter orbits.

Bar fraction and strength decrease mildly with increasing clustercentric radius.

Abstract

Using N-body simulations we study the formation and evolution of tidally induced bars in disky galaxies in clusters. Our progenitor is a massive, late-type galaxy similar to the Milky Way, composed of an exponential disk and an NFW dark matter halo. We place the galaxy on four different orbits in a Virgo-like cluster and evolve it for 10 Gyr. As a reference case we also evolve the same model in isolation. Tidally induced bars form on all orbits soon after the first pericenter passage and survive until the end of the evolution. They appear earlier, are stronger, longer and have lower pattern speeds for tighter orbits. Only for the tightest orbit the properties of the bar are controlled by the orientation of the tidal torque from the cluster at pericenters. The mechanism behind the formation of the bars is the angular momentum transfer from the galaxy stellar component to its halo. All bars undergo extended periods of buckling instability that occur earlier and lead to more pronounced boxy/peanut shapes when the tidal forces are stronger. Using all simulation outputs of galaxies at different evolutionary stages we construct a toy model of the galaxy population in the cluster and measure the average bar strength and bar fraction as a function of clustercentric radius. Both are found to be mildly decreasing functions of radius. We conclude that tidal forces can trigger bar formation in cluster cores, but not in the outskirts, and thus cause larger concentrations of barred galaxies towards cluster center.