a) Overlay of the HST Paα emission map (in contours as in Fig. 15c) on the HCN(4–3)/CO(3–2) brightness temperature ratio map (in color scale and T_mb units). b) Same as a) but showing the HCO⁺(4–3)/CO(3–2) brightness temperature ratio map. c) Same as a) but showing the HCN(4–3)/HCO⁺(4–3) brightness temperature ratio map. All the ratio maps have been derived at the spatial resolution of the CO(3–2) observations ( at PA = 60°; ellipses in lower left corners).