The origin of type-I profiles in cluster lenticulars: An interplay between ram pressure stripping and tidally-induced spiral migration

TL;DR

This study uses simulations to show that the interplay between ram pressure stripping and tidally-induced spiral migration transforms galaxy density profiles from type II to type I in cluster environments, affecting age distributions.

Contribution

It demonstrates how combined effects of tidal spirals and ram pressure stripping explain the origin of type-I profiles in cluster lenticulars, a novel insight into galaxy evolution.

Findings

Type II profiles remain in isolated galaxies.

Profiles become more type I-like with deeper cluster penetration.

Age profiles flatten in cluster lenticulars with type I profiles.

Abstract

Using $N$-body+SPH simulations of galaxies falling into a cluster, we study the evolution of their radial density profiles. When evolved in isolation, galaxies develop a type~II (down-bending) profile. In the cluster, the evolution of the profile depends on the minimum cluster-centric radius the galaxy reaches, which controls the degree of ram pressure stripping. If the galaxy falls to $\sim 50\%$ of the virial radius, then the profile remains type~II, but if the galaxy reaches down to $\sim 20\%$ of the virial radius the break weakens and the profile becomes more type~I like. The velocity dispersions are only slightly increased in the cluster simulations compared with the isolated galaxy; random motion therefore cannot be responsible for redistributing material sufficiently to cause the change in the profile type. Instead we find that the joint action of radial migration driven by tidally-induced spirals and the outside-in quenching of star formation due to ram pressure stripping alters the density profile. As a result, this model predicts a flattening of the age profiles amongst cluster lenticulars with type~I profiles, which can be observationally tested. %