Dynamically driven star formation in models of NGC 7252

We present new dynamical models of the merger remnant NGC 7252 which include star formation simulated according to various phenomenological rules. By using interactive software to match our model with the observed morphology and gas velocity field, we obtain a consistent dynamical model for NGC 7252. In our models, this proto-elliptical galaxy formed by the merger of two similar gas-rich disc galaxies which fell together with an initial pericentric separation of ~2 disc scalelengths approximately 620Myr ago. Results from two different star formation rules - density-dependent and shock-induced - show significant differences in star formation during and after the first passage. Shock-induced star formation yields a prompt and wide-spread starburst at the time of first passage, while density-dependent star formation predicts a more slowly rising and centrally concentrated starburst. A comparison of the distributions and ages of observed clusters with results of our simulations favours shock-induced mechanism of star formation in NGC 7252. We also present simulated colour images of our model of NGC 7252, constructed by incorporating population synthesis with radiative transfer and dust attenuation. Overall, the predicted magnitudes and colours of the models are consistent with observations, although the simulated tails are fainter and redder than observed. We suggest that a lack of star formation in the tails, reflected by the redder colours, is due to an incomplete description of star formation in our models rather than insufficient gas in the tails.