Excess of line-of-sight velocity of the ionised gas with respect to the stars (v_gas−v_stars) as given by y = | v_{0.1 gas} | − | v_{99.9 stars} | for [OIII] (upper panel) and for Hα (bottom panel). For display purposes, only the less noisy bins are plotted, i.e. only bins with either σ_y< 50 km s^-1 or | y | ≥ 2σ_y. As explained in Sect. 3.4, the quantity y is a reliable tracer of ionised outflows only when it is positive. The Spearman rank correlation coefficient (0 < | ρ | < 1, higher values of | ρ | indicate stronger correlation, ρ< 0 if there is an anti-correlation) is reported in each plot, along with the corresponding two-sided p value (if the p value is ≤ α, where α = 0.05 is the level of significance, the observed correlation is statistically significant).