Formation of S0 galaxies through mergers. Bulge-disc structural coupling
  resulting from major mergers
  Observations reveal a strong structural coupling between bulge and disc in S0
galaxies, which seems difficult to explain if they have formed from supposedly
catastrophic events such as major mergers. We face this question by quantifying
the bulge-disc coupling in dissipative simulations of major and minor mergers
that result in realistic S0s. We have studied the dissipative N-body binary
merger simulations from the GalMer database that give rise to realistic,
relaxed E/S0 and S0 remnants (67 major and 29 minor mergers). We simulate
surface brightness profiles of these S0-like remnants in the K-band, mimicking
typical observational conditions, to perform bulge-disc decompositions
analogous to those carried out in real S0s. The global bulge-disc structure of
these remnants has been compared with real data, and they distribute in the B/T
- r_e - h_d parameter space consistently with real bright S0s, where B/T is the
bulge-to-total luminosity ratio, r_e is the bulge effective radius, and h_d is
the disc scalelength. Major mergers can rebuild a bulge-disc coupling in the
remnants after having destroyed the structures of the progenitors, whereas
minor mergers directly preserve them. Remnants exhibit B/T and r_e/h_d spanning
a wide range of values, and their distribution is consistent with observations.
Many remnants have bulge Sersic indices ranging 1<n<2, flat appearance, and
contain residual star formation in embedded discs, a result which agrees with
the presence of pseudobulges in real S0s. Contrary to the popular view, mergers
(and in particular, major events) can result in S0 remnants with realistically
coupled bulge-disc structures in less than ~3 Gyr. In conclusion, the
bulge-disc coupling and the presence of pseudobulges in real S0s cannot be used
as an argument against the possible major-merger origin of these galaxies.
