Formation of S0s in extreme environments II: the star-formation
  histories of bulges, discs and lenses
  Different processes have been proposed to explain the formation of S0s,
including mergers, disc instabilities and quenched spirals. These processes are
expected to dominate in different environments, and thus leave characteristic
footprints in the kinematics and stellar populations of the individual
components within the galaxies. New techniques enable us to cleanly disentangle
the kinematics and stellar populations of these components in IFU observations.
In this paper, we use buddi to spectroscopically extract the light from the
bulge, disc and lens components within a sample of 8 S0 galaxies in extreme
environments observed with MUSE. While the spectra of bulges and discs in S0
galaxies have been separated before, this work is the first to isolate the
spectra of lenses. Stellar populations analysis revealed that the bulges and
lenses have generally similar or higher metallicities than the discs, and the
$\alpha$-enhancement of the bulges and discs are correlated, while those of the
lenses are completely unconnected to either component. We conclude that the
majority of the mass in these galaxies was built up early in the lifetime of
the galaxy, with the bulges and discs forming from the same material through
dissipational processes at high redshift. The lenses, on the other hand, formed
over independent timescales at more random times within the lifetime of the
galaxy, possibly from evolved bars. The younger stellar populations and
asymmetric features seen in the field S0s may indicate that these galaxies have
been affected more by minor mergers than the cluster galaxies.
