Median stack of all spectra sampled from the extended region of the CMZ. The median is shown as a line and the shaded region gives the 95% confidence interval on this value. The black squares in Fig. 2 indicate the positions from which spectra were extracted for this composite spectrum. The black lines indicate the positions of the C₂H components in each N transition, Doppler shifted by 255 km s⁻¹, the LSR velocity of NGC 253.