Building gas rings and rejuvenating S0 galaxies through minor mergers

Abstract

We investigate the effects of minor mergers between an S0 galaxy and a gas-rich satellite galaxy, by means of N-body/smoothed particle hydrodynamics simulations. The satellite galaxy is initially on a nearly parabolic orbit and undergoes several periapsis passages before being completely stripped. In most simulations, a portion of the stripped gas forms a warm dense gas ring in the S0 galaxy, with a radius of ∼6-13 kpc and a mass of ∼10 7 M . The ring is generally short-lived ( 3 Gyr) if it forms from prograde encounters, while it can live for more than 6 Gyr if it is born from counter-rotating or non-coplanar interactions. The gas ring keeps memory of the initial orbit of the satellite galaxy: it is corotating (counter-rotating) with the stars of the disc of the S0 galaxy, if it originates from prograde (retrograde) satellite orbits. Furthermore, the ring is coplanar with the disc of the S0 galaxy only if the satellite's orbit was coplanar, while it lies on a plane that is inclined with respect to the disc of the S0 galaxy by the same inclination angle as the orbital plane of the satellite galaxy. The fact that we form polar rings as long-lived and as massive as co-planar rings suggests that rings can form in S0 galaxies even without strong bar resonances. Star formation up to 0.01 M yr −1 occurs for >6 Gyr in the central parts of the S0 galaxy as a consequence of the interaction. We discuss the implications of our simulations for the rejuvenation of S0 galaxies in the local Universe.

Spiral-like star-forming patterns in CALIFA early-type galaxies

“…Regardless of the environmental properties of present-day ETGs and of whether their SF activity is viewed from the perspective of quenching or rejuvenation that is possibly driven by minor merges (e.g., Mapelli et al 2015), it is important to explore how the amplitude and spatial properties of low-level SF in these systems are related to their gas mass fraction and B/T ratio, how the SFR surface density and stellar initial mass function (IMF) change as the cold-gas supply is gradually depleted, and what intrinsic properties determine whether SF is spatially organized in contiguous rims or spiral-arm-like patterns, rather than in a diffuse and/or patchy collection of faint H regions.…”

Back to the Green Valley: How to Rejuvenate an S0 Galaxy through Minor Mergers

“…This proceeding summarizes the results published in [16]. By means of N-body/smoothed-particle hydrodynamics (SPH) simulations (described in Section 2), we show that minor mergers with gas-rich satellite galaxies can efficiently re-activate star formation in S0 galaxies (Section 3.1).…”

“…The adopted orbits are nearly parabolic (eccentricity e = 1.003, specific orbital energy E s = 3.8 ×10 3 km 2 ·s −2 , specific orbital angular momentum L s = 2.0 × 10 3 km·s −1 kpc, impact parameter b = 10 kpc), in agreement with predictions from cosmological simulations. More details on the simulations can be found in Table 1 and in [16].…”

“…Finally, in run 3, the orbit of the secondary galaxy is polar with respect to the disc of the main galaxy. Runs 1, 2 and 3 correspond to runs A, B and D in [16].…”

“…At the end of the simulation, most of the stars that initially belonged to the dwarf galaxy reside in tidal streams and shells surrounding the S0 galaxy. They end up forming a stellar halo with distance >50 kpc from the centre of the S0 galaxy (see Figures 6 and 7 of [16]). …”