Left: map of peak intensity ratios of the ¹²CO 3–2/6–5 lines. Right: model of the CO 3–2/CO 6–5 line intensity ratio as function of temperature and density. The red region represents the observed range for IRAS 4A, and the yellow range for IRAS 4B. The CO column density is taken to be 10¹⁷ cm^-2 with a line width of 10 km s^-1, these conditions are chosen because they are representative of the observed CO 6–5 flux and line width. The colored lines give the range of densities within the 20″ beam for the two sources based on the models of Kristensen et al. (2012). In the relevant density range, smaller ratios are indicative of higher temperatures.