Early Science with the Large Millimeter Telescope: Observations of dust
  continuum and CO emission lines of cluster-lensed submillimetre galaxies at
  z=2.0-4.7
  We present Early Science observations with the Large Millimeter Telescope,
AzTEC 1.1 mm continuum images and wide bandwidth spectra (73-111 GHz) acquired
with the Redshift Search Receiver, towards four bright lensed submillimetre
galaxies identified through the Herschel Lensing Survey-snapshot and the
SCUBA-2 Cluster Snapshot Survey. This pilot project studies the star formation
history and the physical properties of the molecular gas and dust content of
the highest redshift galaxies identified through the benefits of gravitational
magnification. We robustly detect dust continuum emission for the full sample
and CO emission lines for three of the targets. We find that one source shows
spectroscopic multiplicity and is a blend of three galaxies at different
redshifts (z=2.040, 3.252 and 4.680), reminiscent of previous high-resolution
imaging follow-up of unlensed submillimetre galaxies, but with a completely
different search method, that confirm recent theoretical predictions of
physically unassociated blended galaxies. Identifying the detected lines as
12CO (J_up=2-5) we derive spectroscopic redshifts, molecular gas masses, and
dust masses from the continuum emission. The mean H_2 gas mass of the full
sample is (2.0 +- 0.2) x 10^11 M_sun/\mu, and the mean dust mass is (2.0+-0.2)
x 10^9 M_sun/\mu, where \mu=2-5 is the expected lens amplification. Using these
independent estimations we infer a gas-to-dust ratio of \delta_GDR=55-75, in
agreement with other measurements of submillimetre galaxies. Our magnified
high-luminosity galaxies fall on the same locus as other high-redshift
submillimetre galaxies, extending the L'_CO - L_FIR correlation observed for
local luminous and ultraluminous infrared galaxies to higher FIR and CO
luminosities.
