R₂₁ against galactocentric radius. The circular shaped markers represent all of the R₂₁ values for the central 20″ ≈ 745 pc coloured by their f_dense. The different sizes show their varying signal-to-noise ratio in CO(2−1). Additionally, we overplot the contours of the three different regions: The cyan colour refers to the nuclear region (NUC), the green to the northern bar end (NBE) and the magenta to the southern bar end (SBE). Along the galactocentric radius, we find in the centre higher R₂₁ values, an initial steady decrease followed by a gradual increase. R₂₁ towards NBE is higher than expected (more in Sect. 6.1).