Determining the stellar masses of submillimetre galaxies: the critical
  importance of star formation histories
  Submillimetre (submm) galaxies are among the most rapidly star-forming and
most massive high-redshift galaxies; thus, their properties provide important
constraints on galaxy evolution models. However, there is still a debate about
their stellar masses and their nature in the context of the general galaxy
population. To test the reliability of their stellar mass determinations, we
used a sample of simulated submm galaxies for which we derived stellar masses
via spectral energy distribution (SED) modelling (with Grasil, Magphys, Hyperz
and LePhare) adopting various star formation histories (SFHs). We found that
the assumption of SFHs with two independent components leads to the most
accurate stellar masses. Exponentially declining SFHs (tau) lead to lower
masses (albeit still consistent with the true values), while the assumption of
single-burst SFHs results in a significant mass underestimation. Thus, we
conclude that studies based on the higher masses inferred from fitting the SEDs
of real submm galaxies with double SFHs are most likely to be correct, implying
that submm galaxies lie on the high-mass end of the main sequence of
star-forming galaxies. This conclusion appears robust to assumptions of whether
or not submm galaxies are driven by major mergers, since the suite of simulated
galaxies modelled here contains examples of both merging and isolated galaxies.
We identified discrepancies between the true and inferred stellar ages (rather
than the dust attenuation) as the primary determinant of the success/failure of
the mass recovery. Regardless of the choice of SFH, the SED-derived stellar
masses exhibit a factor of ~2 scatter around the true value; this scatter is an
inherent limitation of the SED modelling due to simplified assumptions.
Finally, we found that the contribution of active galactic nuclei does not have
any significant impact on the derived stellar masses.
