Predicted SNe Ia rate as a function of galactic age. The x-axis refers to the time elapsed since the formation of the galaxy, so T = 0 Gyr indicates the initial stage and T = 14 Gyr the present time, as opposed to the x-axis of the panels on the right column of Fig. 7, which represents the age of the stellar population that contributes to the spectrum (so T = 0 Gyr represents the youngest stellar and T = 14 Gyr the stellar population formed in the initial stage of the galaxy).