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

TL;DR

This study uses N-body simulations to analyze the photometric evolution of gas-rich galaxy mergers, revealing dust obscuration effects and correlations between infrared luminosity and star formation during starbursts.

Contribution

It provides new insights into the dust obscuration effects and photometric stability of ULIRGs during mergers, based on chemodynamical simulations.

Findings

Colors and magnitudes remain stable during starbursts due to dust obscuration.

Younger stars are more heavily obscured by dust than older stars.

Infrared luminosity correlates positively with star formation rate.

Abstract

By performing N-body simulations of chemodynamical evolution of galaxies with dusty starbursts, we investigate photometric evolution of gas-rich major mergers 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 major merger do not change with time significantly, because interstellar dust heavily obscures young starburst populations that could cause rapid evolution of photometric properties of the merger. (2) Dust extinction of stellar populations in a galaxy merger with large infrared luminosity ($L_{\rm IR}$ $>$ $10^{11}$ $L_{\odot}$) is selective in the sense that younger stellar populations are preferentially obscured by dust than old ones. This is because younger populations are located in the central region where a larger amount of dusty interstellar gas can be transferred from the outer gas-rich regions of the merger. (3) Both $L_{\rm IR}$ and the ratio of $L_{\rm IR}$ to $B$ band luminosity $(L_{\rm B}$) increases as the star formation rate increase during the starburst of the present merger model, resulting in the positive correlation between $L_{\rm IR}$ and $L_{\rm IR}/L_{\rm B}$.