SDSS-IV MaNGA: The Formation Sequence of S0 Galaxies

TL;DR

This study analyzes stellar populations in 279 lenticular galaxies from the MaNGA survey, revealing two distinct formation pathways linked to galaxy mass, with implications for understanding their evolutionary origins.

Contribution

It provides the first detailed comparison of bulge and disk stellar populations across a large sample of S0 galaxies, highlighting mass-dependent formation mechanisms.

Findings

Massive S0s have older, metal-rich bulges and disks, suggesting inside-out quenching.

Low-mass S0s show younger bulges than disks, indicating possible bulge rejuvenation.

Environment has little impact on the stellar population properties of S0 galaxies.

Abstract

Gas stripping of spiral galaxies or mergers are thought to be the formation mechanisms of lenticular galaxies. In order to determine the conditions in which each scenario dominates, we derive stellar populations of both the bulge and disk regions of 279 lenticular galaxies in the MaNGA survey. We find a clear bimodality in stellar age and metallicity within the population of S0s and this is strongly correlated with stellar mass. Old and metal-rich bulges and disks belong to massive galaxies, and young and metal-poor bulges and disks are hosted by low-mass galaxies. From this we conclude that the bulges and disks are co-evolving. When the bulge and disk stellar ages are compared, we find that the bulge is almost always older than the disk for massive galaxies ($\textrm{M}_{\star} > 10^{10}~\textrm{M}_{\odot}$). The opposite is true for lower mass galaxies. We conclude that we see two separate populations of lenticular galaxies. The old, massive, and metal-rich population possess bulges that are predominantly older than their disks, which we speculate may have been caused by morphological or inside-out quenching. In contrast, the less massive and more metal-poor population have bulges with more recent star formation than their disks. We postulate they may be undergoing bulge rejuvenation (or disk fading), or compaction. Environment doesn't play a distinct role in the properties of either population. Our findings give weight to the notion that while the faded spiral scenario likely formed low-mass S0s, other processes, such as mergers, may be responsible for high-mass S0s.