Structure, Kinematics, and Chemical Enrichment Patterns after Major
  Gas-Rich Disc-Disc Mergers
  We used an N-body smoothed particle hydrodynamics algorithm, with a detailed
treatment of star formation, supernovae feedback, and chemical enrichment, to
perform eight simulations of mergers between gas-rich disc galaxies. We vary
the mass ratio of the progenitors, their rotation axes, and their orbital
parameters and analyze the kinematic, structural, and chemical properties of
the remnants. Six of these simulations result in the formation of a merger
remnant with a disc morphology as a result of the large gas-fraction of the
remnants. We show that stars formed during the merger (a sudden starburst occur
in our simulation and last for 0.2-0.3 Gyr) and those formed after the merger
have different kinematical and chemical properties. The first ones are located
in thick disc or the halo. They are partially supported by velocity dispersion
and have high [alpha/Fe] ratios even at metallicities as high as [Fe/H]=-0.5.
The former ones -- the young component -- are located in a thin disc
rotationally supported and have lower [alpha/Fe] ratios. The difference in the
rotational support of both components results in the rotation of the thick disc
lagging that of the thin disc by as much as a factor of two, as recently
observed.We find that, while the kinematic and structural properties of the
merger remnant depends strongly upon the orbital parameters of the mergers,
there is a remarkable uniformity in the chemical properties of the mergers.
This suggests that general conclusions about the chemical signature of gas-rich
mergers can be drawn.
