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In recent work (Hayward et al. 2011a) we have suggested that the high-redshift (z ∼ 2 − 4) bright submillimetre galaxy (SMG) population is heterogeneous, with major mergers con-tributing both at early stages, where quiescently star-forming discs are blended into one submm source (‘galaxy-pair SMGs’), and late stages, where mutual tidal torques drive gas inflows and cause strong starbursts. Here we combine hydrodynamic simulations of major mergers with 3-D dust radiative transfer calculations to determine observational diagnos-tics that can distinguish between quiescently star-forming SMGs and starburst SMGs via integrated data alone. We fit the far-IR SEDs of the simulated galaxies with the optically thin single-temperature modified blackbody, the full form of the single-temperature modified blackbody, and a power-law temperature-distribution model. The effective dust temperature, Td, and power-law index of the dust emissivity in the far-IR, β, derived can significantly de-pend on the fitting form used, and the intrinsic β of the dust is not recovered. However, for all forms used here, there is Td above which almost all simulated galaxies are starbursts, so a Td cut is very effective at selecting starbursts. Simulated merger-induced starbursts also have
Hayward et al. (Mon,) studied this question.