a) Optical depths of the 3.05 μm H₂O ice band vs. the 3.47 μm band. Filled (black) and open (green) squares represent data points of the LMC high-mass YSOs (this work) and Galactic high-mass YSOs (see Table 6 for references). The upward and downward triangles represents the lower and upper limit. Solid (black) and dashed (green) lines represent the results of a straight-line fit to LMC and Galactic data points, respectively. The best-fit line is τ_3.47 = 0.044τ_3.05−0.030 for the LMC, and τ_3.47 = 0.043τ_3.05−0.008 for our Galaxy. The straight-line fit without upper limit points is also shown with black dashed line for the LMC data. The figure shows that the slope of the τ_3.47 and τ_3.05 correlation is similar between the LMC and Galactic sources. b) Optical depth ratio of τ_3.47/τ_3.05 vs. τ_3.05. The symbols are same as in the left panel. For the LMC sources with τ_3.05< 2, the τ_3.47/τ_3.05 ratio is significantly lower than Galactic sources, which suggests the presence of threshold τ_3.05 for the appearance of the 3.47 μm band in the LMC.