The physical properties and the evolution of the interacting system
  AM1204-292
  We investigate the interaction effects in the stellar and gas kinematics,
stellar population and ionized gas properties in the interacting galaxy pair
AM1209-292, composed by NGC4105 and NGC4106. The data consist of long-slit
spectra in the range of 3000-7050 {\AA}. The massive E3 galaxy NGC4105 presents
a flat stellar velocity profile, while the ionized gas is in strong rotation,
suggesting external origin. Its companion, NGC4106, shows asymmetries in the
radial velocity field, likely due to the interaction. The dynamics of the
interacting pair was modeled using P-Gadget3 TreePM/SPH code, from which we
show that the system has just passed the first perigalacticum, which triggered
an outbreak of star formation, currently at full maximum. We characterized the
stellar population properties using the stellar population synthesis code
STARLIGHT and, on average, both galaxies are predominantly composed of old
stellar populations. NGC4105 has a slightly negative age gradient, comparable
to that of the most massive elliptical galaxies, but a steeper metallicity
gradient. The SB0 galaxy NGC4106 presents smaller radial variations in both age
and metallicity in comparison with intermediate mass early-type galaxies. These
gradients have not been disturbed by the interaction since the star formation
happened very recently and was not extensive in mass. Electron density
estimates for the pair are systematically higher than those obtained in
isolated galaxies. The central O/H abundances were obtained from
photoionization models in combination with emission line ratios, which resulted
in 12+log(O/H)=9.03+/-0.02 and 12+log(O/H)=8.69+/-0.05 for NGC4105 and NGC4106,
respectively.
