Ammonia from cold high-mass clumps discovered in the inner Galactic disk
  by the ATLASGAL survey
  The APEX Telescope Large Area Survey: The Galaxy (ATLASGAL) is an unbiased
continuum survey of the inner Galactic disk at 870 \mu m. It covers +/- 60 deg
in Galactic longitude and aims to find all massive clumps at various stages of
high-mass star formation in the inner Galaxy, particularly the earliest
evolutionary phases. We aim to determine properties such as the gas kinetic
temperature and dynamics of new massive cold clumps found by ATLASGAL. Most
importantly, we derived their kinematical distances from the measured line
velocities. We observed the ammonia (J,K) = (1,1) to (3,3) inversion
transitions toward 862 clumps of a flux-limited sample of submm clumps detected
by ATLASGAL and extracted 13CO (1-0) spectra from the Galactic Ring Survey
(GRS). We determined distances for a subsample located at the tangential points
(71 sources) and for 277 clumps whose near/far distance ambiguity is resolved.
Most ATLASGAL clumps are cold with rotational temperatures from 10-30 K. They
have a wide range of NH3 linewidths, which by far exceeds the thermal
linewidth, as well as a broad distribution of high column densities with an NH3
abundance in the range of 5 to 30 * 10^{-8}. We found an enhancement of clumps
at Galactocentric radii of 4.5 and 6 kpc. The high detection rate (87%)
confirms ammonia as an excellent probe of the molecular content of the massive,
cold clumps revealed by ATLASGAL. A clear trend of increasing rotational
temperatures and linewidths with evolutionary stage is seen for source samples
ranging from 24 \mu m dark clumps to clumps with embedded HII regions. The
survey provides the largest ammonia sample of high-mass star forming clumps and
thus presents an important repository for the characterization of statistical
properties of the clumps and the selection of subsamples for detailed,
high-resolution follow-up studies.
