Most Submillimetre Galaxies are Major Mergers
  We analyse subarcsecond resolution interferometric CO line data for twelve
sub-millimetre-luminous (S850um > 5mJy) galaxies with redshifts between 1 and
3, presenting new data for four of them. Morphologically and kinematically most
of the twelve systems appear to be major mergers. Five of them are
well-resolved binary systems, and seven are compact or poorly resolved. Of the
four binary systems for which mass measurements for both separate components
can be made, all have mass ratios of 1:3 or closer. Furthermore, comparison of
the ratio of compact to binary systems with that observed in local ULIRGs
indicates that at least a significant fraction of the compact SMGs must also be
late-stage mergers. In addition, the dynamical and gas masses we derive are
most consistent with the lower end of the range of stellar masses published for
these systems, favouring cosmological models in which SMGs result from mergers.
These results all point to the same conclusion, that likely most of the bright
SMGs with L_IR > 5x10e12L_sun are major mergers.
