Hot-to-cold gas mass ratios. Upper panel: Change of the ratio (in log units) of the hot-to-cold molecular gas mass surface density ratios with L_X estimated from the CO and 2.1 μm line emissions at the two spatial scales analyzed in this work: r ≤ 50 pc (${\mathrm{\Sigma }}_{50}^{\mathrm{hot}}$/${\mathrm{\Sigma }}_{50}^{\mathrm{gas}}$) and r ≤ 200 pc (${\mathrm{\Sigma }}_{200}^{\mathrm{hot}}$/${\mathrm{\Sigma }}_{200}^{\mathrm{gas}}$). Lower panel: Hot-to-cold molecular gas mass surface density ratio measured at r ≤ 50 pc as a function of L_X. All symbols as in Fig. 2.