Creating S0s with major mergers: a 3D view

TL;DR

This paper investigates how major galaxy mergers can lead to the formation of S0 galaxies, showing through simulations that disks can be destroyed and regrown, aligning with observed properties and challenging fading scenarios.

Contribution

It demonstrates via 3D simulations that major mergers can produce S0 galaxies with realistic structures, supporting mergers as a key formation mechanism.

Findings

Disks are destroyed and regrown in merger simulations.

Simulated S0s match observed photometric relations.

Mergers explain the angular momentum and concentration mismatch.

Abstract

A number of simulators have argued that major mergers can sometimes preserve discs (e.g. Springel & Hernquist 2005), but the possibility that they could explain the emergence of lenticular galaxies (S0s) has been generally neglected. In fact, observations of S0s reveal a strong structural coupling between their bulges and discs, which seems difficult to reconcile with the idea that they come from major mergers. However, in Querejeta et al. (2015a) we have used N-body simulations of binary mergers to show that, under favourable conditions, discs are first destroyed but soon regrow out of the leftover debris, matching observational photometric scaling relations (e.g. Laurikainen et al. 2010). Additionally, in Querejeta et al. (2015b) we have shown how the merger scenario agrees with the recent discovery that S0s and most spirals are not compatible in an angular momentum--concentration plane. This important result from CALIFA constitutes a serious objection to the idea that spirals transform into S0s mainly by fading (e.g. via ram-pressure stripping, as that would not explain the observed simultaneous change in $\lambda_\mathrm{Re}$ and concentration), but our simulations of major mergers do explain that mismatch. From such a 3D comparison we conclude that mergers must be a relevant process in the build-up of the current population of S0s.