The AT-LESS CO(1-0) survey of submillimetre galaxies in the Extended
  Chandra Deep Field South: First results on cold molecular gas in galaxies at
  z ~ 2
  We present the first results from our on-going Australia Telescope Compact
Array survey of CO(1-0) in ALMA-identified submillimetre galaxies in the
Extended Chandra Deep Field South. Strong detections of CO(1-0) emission from
two submillimetre galaxies, ALESS 122.1 (z = 2.0232) and ALESS 67.1 (z =
2.1230), were obtained. We estimate gas masses of M_gas ~ 1.3 \times 10^{11}
M_odot and M_gas ~ 1.0 \times 10^{11} M_\odot for ALESS 122.1 and ALESS 67.1,
respectively, adopting alpha_CO = 1.0. Dynamical mass estimates from the
kinematics of the CO(1-0) line yields M_dyn (sin i)^2 = 2.1 +- 1.1 \times
10^{11} M_odot and (3.2 +- 0.9) \times 10^{11} M_\odot for ALESS 122.1 and
ALESS 67.1, respectively. This is consistent with the total baryonic mass
estimates of these two systems. We examine star formation efficiency using the
L_FIR versus L'_CO(1-0) relation for samples of local ULIRGs and LIRGs, and
more distant star-forming galaxies, with CO(1-0) detections. We find some
evidence of a shallower slope for ULIRGs and SMGs compared to less luminous
systems, but a larger sample is required for definite conclusions. We determine
gas-to-dust ratios of 170 +- 30 and 140 +- 30 for ALESS 122.1 and ALESS 67.1,
respectively, showing ALESS 122.1 has an unusually large gas reservoir. By
combining the 38.1 GHz continuum detection of ALESS 122.1 with 1.4 and 5.5 GHz
data, we estimate that the free-free contribution to radio emission at 38.1 GHz
is 34 +- 17 microJy, yielding a star formation rate (1400 +- 700 M_\odot
yr^{-1}) consistent with that from the infrared luminosity.
