Comparison between the simultaneous fit to the absorption and emission components of the Hγ line for two spaxels in Tololo 1937-423. Upper panel: spectrum of spaxel (21, 22) around Hγ, together with the best fit (red solid line; the dashed green line represents the fitted continuum). Here the unconstrained fit provides a good match to the line profile. Central panel: unconstrained fit to spaxel (22, 18), which clearly fails to fit the continuum and overestimates the absorption component. Bottom panel: constrained fit, which is more physically sound, while yielding a slightly higher χ2 value.