Simulated r-band flux as a function of the galaxy age and SFR, assuming a constant star formation history. The solid and dashed black lines are the 1σ and 2σ confidence intervals of the r flux estimation measured with MUSE data by Fumagalli et al. (2017). The dashed white line marks the age of the Universe at z = 3.25, i.e., t = 1.97 Gyr. The r-band flux is more sensitive to the instantaneous SFR and, under the assumption of a constant star formation history used in this case, does not depend on the age of the galaxy.