D_n4000 (top panel) and H_δ (bottom panel) as a function of Σ₁ (mass-to-size ratio), for AGN (red circles) and galaxies (blue contours). AGN do not have Σ₁ values lower than 9.0, whereas sources in the reference catalogue go down to 7.5. This implies that AGN reside in more compact systems compared to non-AGN. Both populations present an increase of D_n4000 and a decrease of H_δ with Σ₁, at Σ₁ ≥ 9.5.