Warm-to-cold gas mass ratio as a function of the α conversion factor. The circle shows the ratio’s lower limit in the outflow for α = 0.8 M_⊙/(K km s^-1 pc²). The solid line shows how this lower limit decreases as α approaches values thought appropriate for the Milky Way. This curve brackets the range of all acceptable M_warm/M_cold values in the outflow (hatched area), under the assumption that the 400 K outflowing gas fraction probed by the CO is negligible compared to the fraction probed by the  H₂. For the ambient medium, the measuredratio (triangles) and its dependence on α (non-solid lines) are given for different warm gas content scenarios: when only the mass of the 400 K  H₂ gas directly seen by Spitzer is used (dashed line) and when the mass of another CO-based 400 K gas component is added. The dashed-dotted line uses an additional mass of 2.5 × ⁷ M_⊙ distributed in clouds of 2 × 10⁶ cm^-3 (as in the dashed-dotted CO SLED component in Fig. 11). The dotted line instead uses an additional mass of 2.5 × ⁸ M_⊙ distributed in clouds of 1 × 10⁵ cm^-3 (as in the dotted CO SLED component in Fig. 11). This line constrains the upper range of acceptable M_warm/M_cold values in the ambient medium (solid area).