Archival spectra focussed on the Hβ (left panel) and Hα (right panel) emission lines. The spectra are plotted in continuum subtracted normalised flux to account for any discrepancies in flux calibration, units, or aperture size. The systemic redshift of Hα and Hβ based on the narrow emission lines is indicated by the dashed black line. The Keck spectrum from 2009 is plotted in orange and covers only the Hβ line. Residuals of the SDSS spectrum (2000) minus our MUSE spectrum (2014) are plotted in green to emphasise the change in flux and line shape.