Comparison of the [OIII] and [OII] principal emission line parameters. Left panel: sigma of the [O III] line versus the sigma of the [O II]. The [OIII] lines show broader widths. Right panel: σ excess (defined using the square root of the quadratic difference of the [O III] and [O II] sigma, see text) versus the relative shift of the [O III] peak respect to [O II] peak (both referring to their rest frame position).