Color-scales showing in all three panels the Toomre Q map (see text for details) of the disk seen toward source #1. While the top panel uses the rotational temperature derived from CH₃CN (Fig. 10) at each pixel to determine the sound speed and column density, the middle panel uses a uniform lower temperature of 200 K for these estimates. The lower panel uses a dust temperature distribution of T ∝ r^-0.4 for the calculations (see Sect. 4.3). The black contours show in each panel the 438 μm continuum emission in 4σ steps of 28 mJy beam^-1. Toomre Q values outside the CH₃CN(37₂−36₂) 3σ level (Fig. 10) are clipped out. The beam is shown at the bottom right of each panel.