A survey of molecular gas in luminous sub-millimetre galaxies
  We present the results from a survey for 12CO emission in 40 luminous
sub-millimetre galaxies (SMGs), with 850um fluxes of S850 = 4 - 20 mJy,
conducted with the Plateau de Bure Interferometer. We detect 12CO emission in
32 SMGs at z~1.2 - 4.1, including 16 SMGs not previously published. Using
multiple 12CO line (J_up =2 - 7) observations, we derive a median spectral line
energy distribution for luminous SMGs and use this to estimate a mean gas mass
of (5.3 +/- 1.0) \times 10^10 Msun. We report the discovery of a fundamental
relationship between 12CO FWHM and 12CO line luminosity in high-redshift
starbursts, which we interpret as a natural consequence of the baryon-dominated
dynamics within the regions probed by our observations. We use far-infrared
luminosities to assess the star-formation efficiency in our SMGs, finding a
steepening of the L'CO-LFIR relation as a function of increasing 12CO J_up
transition. We derive dynamical masses and molecular gas masses, and use these
to determine the redshift evolution of the gas content of SMGs, finding that
they do not appear to be significantly more gas rich than less vigorously
star-forming galaxies at high redshifts. Finally, we collate X-ray
observations, and study the interdependence of gas and dynamical properties of
SMGs with their AGN activity and supermassive black hole masses (MBH), finding
that SMGs lie significantly below the local M_BH-sigma relation. We conclude
that SMGs represent a class of massive, gas-rich ultraluminous galaxies with
somewhat heterogeneous properties, ranging from starbursting disc-like systems
with L~10^12 L_sun, to the most highly star-forming mergers in the Universe.
