Hα surface brightness profile in the south, i.e. not affected by the filaments in the north. The points show the observed profile in circular annuli and error-bars are 2σ. The black line indicates the double exponential profile fitted to the outer (r > 5″) profile, while dot-dashed and dashed lines indicate the individual components with scale-lengths r₁ = 1.62″ (447 pc) and r₂ = 8.94″ (2.47 kpc). The grey line indicates the light profile of the central (r ≤ 5″) residual component that is obtained after subtracting the double exponential.