The SCUBA-2 Cosmology Legacy Survey: the nature of bright submm galaxies
  from 2 deg2 of 850-um imaging
  We present physical properties [redshifts (z), star-formation rates (SFRs)
and stellar masses (Mstar)] of bright (S850>4mJy) submm galaxies in the ~2deg2
COSMOS and UDS fields selected with SCUBA-2/JCMT. We complete the galaxy
identification process for all (~2000) S/N>3.5 850-um sources, but focus our
scientific analysis on a high-quality sub-sample of 651 S/N>4 sources with
complete multi-wavelength coverage including 1.1-mm imaging. We check the
reliability of our identifications, and the robustness of the SCUBA-2 fluxes by
revisiting the recent ALMA follow-up of 29 sources in our sample. Considering
>4mJy ALMA sources, our identification method has a completeness of ~86 per
cent with a reliability of ~92 per cent, and only ~15-20 per cent of sources
are significantly affected by multiplicity (when a secondary component
contributes >1/3 of the primary source flux). The impact of source blending on
the 850-um source counts as determined with SCUBA-2 is modest; scaling the
single-dish fluxes by ~0.9 reproduces the ALMA source counts. For our final
SCUBA-2 sample we find median z=2.40+0.10-0.04, SFR=287+-6Moyr-1, and
log(Mstar/Mo)=11.12+-0.02 (the latter for 349/651 sources with optical
identifications). These properties clearly locate bright submm galaxies on the
high-mass end of the 'main sequence' of star-forming galaxies out to z~6,
suggesting that major mergers are not a dominant driver of the high-redshift
submm-selected population. Their number densities are also consistent with the
evolving galaxy stellar mass function. Hence, the submm galaxy population is as
expected, albeit reproducing the evolution of the main sequence of star-forming
galaxies remains a challenge for theoretical models/simulations.
