Top-left: electron density vs electron temperature diagnostic diagram for the core of the M1931 BCG. For this plot, we use the following diagnostics: [N II] λ 5755/6548, [N II] λ 5755/6584, [S II] λ 6731/6716, [Ar IV] λ 4740/4711, and [O III] λ 4363/5007. The intersection of the curves gives the best fit electron temperature and density. Top-right: same as top-left, but for the Hα tail of the BCG. Bottom-left: spatially resolved electron temperature map for the BCG of the M1931 cluster. The colour bar shows the temperature measured in [K], as computed using the PyNeb tool, from the [N II] λ5755/6584 emission lines. Bottom-right: electron density map as computed using the PyNeb tool, from the [S II] λ6731/6716 doublet. The colour-bar depicts the density in units of cm⁻³. The contours in both lower panels show the Hα flux intensity, while the cross shows the location of the AGN.