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Investigating early-type galaxy evolution with a multi-wavelength approach. III. Insights from SPH simulations with chemo-photometric implementation

We are exploring galaxy evolution in low density environments exploiting smooth particle hydrodynamic simulations including chemo-photometric implementation. From a large grid of simulations of galaxy encounters and mergers starting from triaxial halos of gas e dark matter, we single out the simulations matching the global properties of our targets. These simulations are used to give insights into their evolution. We focus on 11 early-type galaxies selected because of their nearly passive stage of evolution in the nuclear region. However, a variety of UV features are detected in more than half of these galaxies. We find no significant differences in the formation mechanisms between galaxies with or without UV features. Major and minor mergers are able to reproduce their peculiar UV morphologies, galaxy encounters are more suitable for 'normal' early-type galaxies. Their star formation rate self-quenches several Gyr later the merger/encounter occurred, via gas exhaustion and stellar feedback, moving the galaxy from blue to red colors, driving the galaxy transformation. The length of the quenching is mass dependent and lasts from 1 to 5 Gyr or more in the less massive systems. All our targets are gas rich at redshift 1. Three of them assembled at most 40% of their current stellar mass at z>1, and seven assembled more than 50% between redshift 0.5 and 1. Their stellar mass grows with 4% by crossing the Green Valley before reaching their current position on the NUV-r vs. Mr diagram.