Upper panel: observed surface brightness of H_α gas. The MCMC fit is shown in blue accompanied by 1σ error (blue shaded area). The first point (open square) is not used in fitting owing to the limitation assigned by Barolo (discussed in Sharma et al. 2021). The value Σ₀ keeps the dimension units/kpc², where units =ergs¹cm⁻²μ⁻¹¹ 1e + 17 km s⁻¹. Lower panel: posterior distribution of Σ₀ and R_gas, where vertical dashed lines show the 16, 50, 84 percentiles from left to right, respectively.