Ammonia from cold high-mass clumps discovered in the inner Galactic disk by the ATLASGAL survey

Context. 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 degrees 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. Aims. 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. Methods. 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 (CO)-C-13 (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. Results. Most ATLASGAL clumps are cold with rotational temperatures from 10-30 K with a median of 17 K. They have a wide range of NH3 linewidths (1-7 kms(-1)) with 1.9 km s(-1) as median, which by far exceeds the thermal linewidth, as well as a broad distribution of high column densities from 10(14) to 10(16) cm(-2) (median of 2 x 10(15) cm(-2)) with an NH3 abundance in the range of 5 to 30 x 10(-8). ATLASGAL sources are massive, greater than or similar to 100 M-circle dot, and a fraction of clumps with a broad linewidth is in virial equilibrium. We found an enhancement of clumps at Galactocentric radii of 4.5 and 6 kpc. The comparison of the NH3 lines as high-density probes with the GRS (CO)-C-13 emission as low-density envelope tracer yields broader linewidths for (CO)-C-13 than for NH3. The small differences in derived clump velocities between NH3 (representing dense core material) and (CO)-C-13 (representing more diffuse molecular cloud gas) suggests that the cores are essentially at rest relative to the surrounding giant molecular cloud. Conclusions. 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.