1998ApJ...508L..13T

Recently Taniguchi and Ohyama found that the higher ¹²CO to ¹³CO integrated intensity ratios at a transition J=1-0, R=I¹²CO)/I(¹³CO≳20, in a sample of starburst merging galaxies such as Arp 220 are mainly attributed to the depression of ¹³CO emission with respect to ¹²CO. Investigating the same sample of galaxies analyzed by Taniguchi and Ohyama, we find that there is a tight, almost linear correlation between the dust mass and ¹³CO luminosity. This implies that dust grains are also depressed in the high-R starburst mergers, leading to the higher dust temperature (T_d_) in them because of the relative increase in the radiation density. Nevertheless, the average dust mass (M_d) of the high-R starburst mergers is significantly higher than that of non-high-R galaxies. This is naturally understood because the galaxy mergers could accumulate a lot of dust grains from their progenitor galaxies together with the supply of dust grains formed newly in the star-forming regions. Since L\fen FIR∝M_dT⁵_d given the dust emissivity law S_ν∝λ^–1, the increases in both M_d and T_d explain well why the starburst mergers are so bright in the far-infrared. We discuss the important role that the superwind activity plays in destroying dust grains as well as dense gas clouds in the central region of mergers.