Back to the green valley: how to rejuvenate an S0 galaxy through minor mergers

TL;DR

This study uses simulations to show that minor mergers with gas-rich dwarfs can rejuvenate S0 galaxies by triggering long-lasting star formation and forming observable gas rings, explaining recent star formation signatures.

Contribution

It demonstrates through simulations that minor mergers can rejuvenate S0 galaxies and produce observable gas rings, clarifying the role of such mergers in galaxy evolution.

Findings

Minor mergers trigger star formation episodes lasting ~10 Gyr.

Gas rings form as a signature of mergers, especially with polar and counter-rotating satellites.

Long-lived smooth gas rings are induced by specific merger orientations.

Abstract

About half of the S0 galaxies in the nearby Universe show signatures of recent or ongoing star formation. Whether these S0 galaxies were rejuvenated by the accretion of fresh gas is still controversial. We study minor mergers of a gas-rich dwarf galaxy with an S0 galaxy, by means of N-body smoothed-particle hydrodynamics simulations. We find that minor mergers trigger episodes of star formation in the S0 galaxy, lasting for ~10 Gyr. One of the most important fingerprints of the merger is the formation of a gas ring in the S0 galaxy. The ring is reminiscent of the orbit of the satellite galaxy, and its lifetime depends on the merger properties: polar and counter-rotating satellite galaxies induce the formation of long-lived smooth gas rings.