Physical Conditions of the Gas in an ALMA [CII]-identified Submillimetre
  Galaxy at z = 4.44
  We present CO(2-1) observations of the submillimetre galaxy ALESS65.1
performed with the Australia Telescope Compact Array at 42.3 GHz. A previous
ALMA study of submillimetre galaxies in the Extended Chandra Deep Field South
detected [CII] 157.74 micron emission from this galaxy at a redshift of z =
4.44. No CO(2-1) emission was detected but we derive a firm upper limit to the
cold gas mass in ALESS65.1 of M_gas < 1.7 x 10^10 M_odot. The estimated gas
depletion timescale is <50 Myr, which is similar to other high redshift SMGs,
and consistent with z > 4 SMGs being the likely progenitors of massive
red-and-dead galaxies at z > 2. The ratio of the [CII], CO and far-infrared
luminosities implies a strong far-ultraviolet field of G_0 > 10^3, as seen in
Galactic star forming regions or local ULIRGs. The observed L_[CII]/L_FIR = 2.3
x 10^{-3} is high compared to local ULIRGs and, combined with L_[CII]/L_CO >
2700, it is consistent with ALESS65.1 either having an extended (several kpc)
[CII] emitting region or lower than solar metallicity.
