Formation of S0s in extreme environments II: the star-formation histories of bulges, discs and lenses

TL;DR

This study uses advanced spectroscopic techniques to analyze the stellar populations of bulges, discs, and lenses in S0 galaxies from extreme environments, revealing distinct formation histories and the role of different processes like mergers and bar evolution.

Contribution

First to isolate and analyze the spectra of lenses in S0 galaxies, providing new insights into their independent formation timescales and processes.

Findings

Bulges and lenses have similar or higher metallicities than discs.

Bulges and discs show correlated $oldsymbol{ m extalpha}$-enhancement; lenses do not.

Lenses likely formed from evolved bars at different times.

Abstract

Different processes have been proposed to explain the formation of S0s, including mergers, disc instabilities and quenched spirals. These processes are expected to dominate in different environments, and thus leave characteristic footprints in the kinematics and stellar populations of the individual components within the galaxies. New techniques enable us to cleanly disentangle the kinematics and stellar populations of these components in IFU observations. In this paper, we use buddi to spectroscopically extract the light from the bulge, disc and lens components within a sample of 8 S0 galaxies in extreme environments observed with MUSE. While the spectra of bulges and discs in S0 galaxies have been separated before, this work is the first to isolate the spectra of lenses. Stellar populations analysis revealed that the bulges and lenses have generally similar or higher metallicities than the discs, and the $\alpha$-enhancement of the bulges and discs are correlated, while those of the lenses are completely unconnected to either component. We conclude that the majority of the mass in these galaxies was built up early in the lifetime of the galaxy, with the bulges and discs forming from the same material through dissipational processes at high redshift. The lenses, on the other hand, formed over independent timescales at more random times within the lifetime of the galaxy, possibly from evolved bars. The younger stellar populations and asymmetric features seen in the field S0s may indicate that these galaxies have been affected more by minor mergers than the cluster galaxies.