BUDDI-MaNGA II: The Star-Formation Histories of Bulges and Discs of S0s

TL;DR

This study uses spectral analysis to investigate the star-formation histories of bulges and discs in S0 galaxies, revealing mass-dependent formation scenarios and multiple evolutionary pathways.

Contribution

It introduces a method to isolate bulge and disc spectra in S0 galaxies and compares their stellar populations, highlighting the influence of galaxy mass on formation processes.

Findings

Bulges are older and more metal-rich than discs.

Massive S0s formed bulges rapidly early, while lower mass S0s formed more gradually.

No significant environmental effect on disc formation or quenching.

Abstract

Many processes have been proposed to explain the quenching of star formation in spiral galaxies and their transformation into S0s. These processes affect the bulge and disc in different ways, and so by isolating the bulge and disc spectra, we can look for these characteristic signatures. In this work, we used BUDDI to cleanly extract the spectra of the bulges and discs of 78 S0 galaxies in the MaNGA Survey. We compared the luminosity and mass weighted stellar populations of the bulges and discs, finding that bulges are generally older and more metal rich than their discs. When considering the mass and environment of each galaxy, we found that the galaxy stellar mass plays a more significant role on the formation of the bulges. Bulges in galaxies with masses $\geq10^{10}M_\odot$ built up the majority of their mass rapidly early in their lifetimes, while those in lower mass galaxies formed over more extended timescales and more recently. No clear difference was found in the formation or quenching processes of the discs as a function of galaxy environment. We conclude that more massive S0 galaxies formed through an inside-out scenario, where the bulge formed first and evolved passively while the disc underwent a more extended period of star formation. In lower mass S0s, the bulges and discs either formed together from the same material, or through an outside-in scenario. Our results therefore imply multiple formation mechanisms for S0 galaxies, the pathway of which is chiefly determined by a galaxy's current stellar mass.