The model assumes that all progenitors of early-type galaxies started forming stars at a time t_start and ended forming stars at a time t_stop. Three possible star formation histories are shown here:

For simplicity, the time t_start is the same for all galaxies in the model. It can be entered directly as a fraction of the present age of the Universe, or as a redshift. If it is entered as a redshift, click "Apply" to calculate the corresponding age of the Universe.