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 \(\sim\)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.
Highlights
S0 galaxies are intriguing objects: they are early-type galaxies (ETGs), but are characterized by a stellar disc
Where do S0 galaxies that lie in the green valley come from? A possible explanation is that S0 galaxies cross the green valley during their transformation from actively star forming to passive galaxies
We studied the merger of a gas-rich dwarf galaxy with an S0 galaxy, by means of N-body/smoothed-particle hydrodynamics (SPH)
Summary
S0 galaxies are intriguing objects: they are early-type galaxies (ETGs), but are characterized by a stellar disc ( with no spiral arms). With respect to the blue cloud (where galaxies have blue colours and are actively star forming) and to the red sequence (i.e., the sequence of red and nearly passive galaxies), galaxies that populate the green valley are red but “not so dead”, i.e., they still form stars at some level. A possible explanation is that S0 galaxies cross the green valley during their transformation from actively star forming to passive galaxies. According to an alternative scenario, star-forming S0 galaxies are “rejuvenated” ETGs: after having already reached the red sequence, they came back to the green valley, because star formation was re-activated thanks to the accretion of fresh gas (Figure 1). An S0 galaxy enters the green valley during its transformation from a star-forming galaxy to a passive galaxy
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