Cold and warm dust along a merging galaxy sequence

Abstract

We investigate the cold and warm dust properties during galaxy interactions using a merging galaxy sample ordered into a chronological sequence from pre- to post-mergers. Our sample comprises a total of 29 merging systems selected to have far-infrared and submillimetre observations. The submillimetre data are mainly culled from the literature, while for five galaxies (NGC 3597, 3690, 6090, 6670 and 7252) the submillimetre observations are presented here for the first time. We use the 100- to 850-μm flux density ratio, f 100/f850, as a proxy for the mass fraction of the warm and cold dust in these systems. We find evidence for an increase in f 100/f850 along the merging sequence from early to advanced mergers, and interpret this trend as an increase of the warm relative to the cold dust mass. We argue that the two key parameters affecting the f 100/f850 flux ratio is the star formation rate and the dust content of individual systems relative to the stars. Using a sophisticated model for the absorption and re-emission of the stellar ultraviolet radiation by dust, we show that these parameters can indeed explain both the increase and the observed scatter in f100/f850 along the merging galaxy sequence. We also discuss our results under the hypothesis that elliptical galaxies are formed via disc galaxy mergers.