An Origin of the Huge Far-Infrared Luminosity of Starburst Mergers

Abstract

Recently Taniguchi and Ohyama found that the higher ${}^{12}$CO to ${}^{13}$CO integrated intensity ratios at a transition $J$=1--0, $R=I{(}^{12}$CO)$/I{(}^{13}$CO) $\gtrsim 20$, in a sample of starburst merging galaxies such as Arp 220 are mainly attributed to the depression of ${}^{13}$CO emission with respect to ${}^{12}$CO. Investigating the same sample of galaxies analyzed by Taniguchi & Ohyama, we find that there is a tight, almost linear correlation between the dust mass and ${}^{13}$CO luminosity. This implies that dust grains are also depressed in the high-$R$ starburst mergers, leading to the higher dust temperature ($T_{\mathrm{d}}$) in them because of the relative increase in the radiation density. Nevertheless, the average dust mass ($M_{\mathrm{d}}$) of the high-$R$ starburst mergers is higher significantly 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 supply of dust grains formed newly in the star forming regions. Since $L$(FIR) $\propto M_{\mathrm{d}}{T}_{\mathrm{d}}^5$ given the dust emissivity law, $S_{\nu }\propto {\lambda }^{-1}$, the increases in both $M_{\mathrm{d}}$ and $T_{\mathrm{d}}$ explain well why the starburst mergers are so bright in the FIR. We discuss that the superwind activity plays an important role in destroying dust grains as well as dense gas clouds in the central region of mergers.

10 pages (aaspp4.sty), 3 postscript figures (embedded). Accepted for publication in Astrophysical Journal Letters

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Cited by in corpus (5)

• Optical Versus Mid-Infrared Spectroscopic Classification of Ultraluminous Infrared Galaxies
• 13CO(J=1-0) Depression in Luminous Starburst Mergers, Revisited
• Redshifts of Galaxies Around Arp 220 and Serendipitous Discovery of Three Star-Forming Dwarf Galaxies at Redshift $z\sim$ 0.5
• Contribution of starburst mergers at z~1 to the strong evolution of infrared and submillimeter deep surveys
• Modelling the evolution of dusty starburst galaxies in multi-band deep surveys