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Matching the number counts and redshift distribution of submillimetergalaxies (SMGs) without invoking modifications to the initial mass function(IMF) has proved challenging for semi-analytic models (SAMs) of galaxyformation. We adopt a previously developed SAM that is constrained to match thez=0 galaxy stellar mass function and makes various predictions that agree wellwith observational constraints; we do not recalibrate the SAM for this work. Weimplement three prescriptions to predict the submillimeter flux densities ofthe model galaxies; two depend solely on star formation rate, whereas the otheralso depends on the dust mass. By comparing the predictions of the models, wefind that taking into account the dust mass, which affects the dust temperatureand thus influences the far-infrared spectral energy distribution, is crucialfor matching the number counts and redshift distribution of SMGs. Moreover,despite using a standard IMF, our model can match the observed SMG numbercounts and redshift distribution reasonably well, which contradicts theconclusions of some previous studies that a top-heavy IMF, in addition totaking into account the effect of dust mass, is needed to match theseobservations. Although we have not identified the key ingredient that isresponsible for our model matching the observed SMG number counts and redshiftdistribution without IMF variation- which is challenging given the differentprescriptions for physical processes employed in the SAMs of interest-ourresults demonstrate that in SAMs, IMF variation is degenerate with otherphysical processes, such as stellar feedback.

Is a top-heavy initial mass function needed to reproduce the submillimeter galaxy number counts?