Massive star formation in the GMC G345.5+1.0: Spatial distribution of
  the dust emission
  We attempt to make a complete census of massive-star formation within all of
GMC G345.5+1.0. This cloud is located one degree above the galactic plane and
at 1.8 kpc from the Sun, thus there is little superposition of dust along the
line-of-sight, minimizing confusion effects in identifying individual clumps.
We observed the 1.2 mm continuum emission across the whole GMC using the
Swedish-ESO Submillimetre Telescope Imaging Bolometer Array mounted on the
SEST. Observations have a spatial resolution of 0.2 pc and cover 1.8 deg\times
2.2 deg in the sky with a noise of 20 mJy/beam. We identify 201 clumps with
diameters between 0.2 and 0.6 pc, masses between 3.0 and 1.3\times10^3 Msun,
and densities between 5\times10^3 and 4\times10^5 cm^-3. The total mass of the
clumps is 1.2\times10^4 Msun, thus the efficiency in forming these clumps,
estimated as the ratio of the total clump mass to the total GMC mass, is 0.02.
The clump mass distribution for masses between 10 and 10^3 Msun is well-fitted
by a power law dN/dM proportional to M^-alpha, with a spectral mass index alpha
of 1.7+/-0.1. Given their mass distribution, clumps do not appear to be the
direct progenitors of single stars. Comparing the 1.2 mm continuum emission
with infrared images taken by the Midcourse Space Experiment (MSX) and by the
SPITZER satellite, we find that at least 20% of the clumps are forming stars,
and at most 80% are starless. Six massive-star forming regions embedded in
clumps and associated with IRAS point sources have mean densities of ~10^5
cm^-3, luminosities >10^3 Lsun, and spectral energy distributions that can be
modeled with two dust components at different mean temperatures of 28+/-5 and
200+/-10 K.
