Simulations of dust in interacting galaxies. I. Dust attenuation

A new Monte Carlo radiative transfer code, SUNRISE, is used in conjunction with hydrodynamic simulations of major galaxy mergers to calculate the effects of dust in such systems. Dust has a profound effect on the emerging radiation, consistent with observations of dust absorption in starburst galaxies. The dust attenuation increases with luminosity such that at peak luminosities similar to 90% of the bolometric luminosity is absorbed by dust. We find that our predictions agree with observed relationships between the UV spectral slope and the fraction of light absorbed by dust (IRX-beta) and observational estimates of the optical depth as a function of intrinsic B-band or UV luminosity. In general, the detailed appearance of the merging event depends on the stage of the merger and the geometry of the encounter. The fraction of bolometric energy absorbed by the dust, however, is a robust quantity that can be predicted from the intrinsic properties bolometric luminosity, baryonic mass, star formation rate, and metallicity of the simulated system. This paper presents fitting formulae, valid over a wide range of masses and metallicities, from which the absorbed fraction of luminosity ( and consequently also the infrared dust luminosity) can be predicted. The attenuation of the luminosity at specific wavelengths can also be predicted, albeit with a larger scatter due to the variation with viewing angle. These formulae for dust attenuation are consistent with earlier studies and would be suitable for inclusion in theoretical models, e. g., semianalytic models, of galaxy formation and evolution.