Relation curves between f_DMG, τ_Hi, and T_ex. Panel a) shows 3D curves with red lines. Relations between each two parameters are projected with black lines. Panel b) shows relation between f_DMG and τ_Hi. The green dashed line represents τ_Hi = 1. The value with τ_Hi = 1 for 33 sources are indicated with red crosses, but for G132.5-1.0, G207.2-1.0, and G347.4+1.0, τ_Hi = 5.4,4.3, and 0.5, respectively. They are shown with red squares. Panel c) shows the relation between f_DMG and T_ex. Panel d) shows the relation between τ_Hi = 1 and T_ex. The meaning of red crosses and blue dashed lines in panels c) and d) are same as in panel b).