Christopher C. Hayward, Peter S. Behroozi, Rachel S. Somerville, Joel R. Primack, Jorge Moreno, Risa H. Wechsler
There is anecdotal evidence that spatially and physically unassociated galaxies blended into a single submillimetre (submm) source contribute to the submm galaxy (SMG) population. However, the significance of this subpopulation has neither been observationally constrained nor theoretically predicted. This work is the first to theoretically predict the contribution of spatially unassociated components to the SMG population. We generate mock SMG catalogues using lightcones derived from the Bolshoi cosmological simulation; to assign submm flux densities to the mock galaxies, we use a fitting function previously derived from the results of dust radiative transfer performed on hydrodynamical simulations of isolated disc and merging galaxies. We then calculate submm number counts for different beam sizes and without blending. Our model suggests that there are a sufficient number of blended SMGs to account for the observed number counts of submm sources with 850-{\mu}m flux density S_850 >~12 mJy. Furthermore, we predict that ~30-80 per cent of blended SMGs have at least one spatially unassociated component. For a 15-arcsec beam, blends of >2 galaxies in which at least one component is spatially unassociated dominate the blended sources with total S_850 >~3 mJy. The distribution of the redshift separations amongst the components is strongly bimodal. The typical redshift separation of spatially unassociated blended sources is ~1. Our predictions for the contributions of spatially unassociated components and the distribution of redshift separations are not testable with currently available data, but they will be easily tested once sufficiently accurate redshifts for the individual subcomponents (resolved by, e.g., ALMA) of a sufficient number of single-dish-detected blended SMGs are available.
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http://arxiv.org/abs/1304.4933
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