Photometric evolution of dusty starburst mergers:On the nature of ultra-luminous infrared galaxies

摘要

By performing N-body simulations of chemodynamical evolution of galaxies withdusty starbursts, we investigate photometric evolution of gas-rich majormergers in order to explore the nature of ultraluminous infrared galaxies(ULIRGs) with the total infrared luminosity ($L_{\rm IR}$ for $8\sim 1000$$\mu$m) of $\sim$ $10^{12}$ $L_{\odot}$. Main results are the following three.(1) Global colors and absolute magnitudes the during dusty starburst of a majormerger do not change with time significantly, because interstellar dust heavilyobscures young starburst populations that could cause rapid evolution ofphotometric properties of the merger. (2) Dust extinction of stellarpopulations in a galaxy merger with large infrared luminosity ($L_{\rm IR}$ $>$$10^{11}$ $L_{\odot}$) is selective in the sense that younger stellarpopulations are preferentially obscured by dust than old ones. This is becauseyounger populations are located in the central region where a larger amount ofdusty interstellar gas can be transferred from the outer gas-rich regions ofthe merger. (3) Both $L_{\rm IR}$ and the ratio of $L_{\rm IR}$ to $B$ bandluminosity $(L_{\rm B}$) increases as the star formation rate increase duringthe starburst of the present merger model, resulting in the positivecorrelation between $L_{\rm IR}$ and $L_{\rm IR}/L_{\rm B}$.