The physical properties and evolution of the interacting system AM 1204−292

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.