Interpreting the galaxy group CG J1720-67.8 through evolutionary synthesis models

This paper is part of a series devoted to a detailed analysis of the properties of the compact group CG J1720- 67.8 and its member galaxies with the aim of shedding light on its evolutionary history. Here we interpret our previously published observational results through comparison with chemically consistent spectrophotometric evolutionary synthesis models to gain further clues to the evolution of the galaxies in this group. In order to reduce the number of free parameters, we considered the simplest case of a single burst of star-formation turned on after 11-12 Gyr of undisturbed galaxy evolution. However, we also briefly explored the effect of multiple, interaction-induced bursts of star-formation. We found that the two spiral galaxies are consistent with interaction-induced strong starbursts switched on similar to 40 to 180 Myr ago and still active. For the early-type galaxy, a less than or similar to 0.9- 1.3 Gyr old star-formation event ( depending on the considered model) appears consistent with the observed properties. The comparison with models cannot rule out the possibility that this galaxy is already the result of a merger. Alternatively, a star-formation episode in this galaxy might have been triggered by gas inflow as a consequence of the interaction with the companion galaxies. Estimates of galaxy masses were derived from the comparison with the models. Finally our results are discussed in comparison with other well-studied, poor galaxy systems.