Evolution of the MW’s R_eff. Left: time evolution of the stellar R_eff under two limiting assumptions: stars remain at their R_birth (red squares), or stars are placed at their presentday radii immediately after formation (circles). Right: R_eff–stellar mass relation, where stellar mass reflects time-dependent mass loss, measured every 0.5 redshift as is shown in black text. The true evolution of R_eff is expected to lie between these two regimes, as is illustrated by the shaded region in both panels, and should be close to the red lines at early epochs, with a tendency towards the blue lines at the present day. In both panels, the dashed green lines are not formal fits but are included as a reference, including from van Dokkum et al. (2013).