摘要：Context.The initial conditions of molecular clumps in which high-mass stars form are poorly understood. In particular, a more detailed study of the earliest evolutionary phases is needed. The APEX Telescope Large Area Survey of the whole inner Galactic disk at 870μm, ATLASGAL, has therefore been conducted to discover high-mass star-forming regions at different evolutionary phases.Aims.We derive properties such as velocities, rotational temperatures, column densities, and abundances of a large sample of southern ATLASGAL clumps in the fourth quadrant.Methods.Using the Parkes telescope, we observed theNH3(1, 1) to (3, 3) inversion transitions towards 354 dust clumps detected by ATLASGAL within a Galactic longitude range between 300°and 359°and a latitude within± 1.5°. For a subsample of 289 sources, theN2H+(1–0) line was measured with the Mopra telescope.Results.We measured a medianNH3(1, 1) line width of~ 2km s-1, rotational temperatures from 12 to 28 K with a mean of 18 K, and source-averagedNH3abundances from1.6 × 10-6to10-8. For a subsample with detectedNH3(2, 2) hyperfine components, we found that the commonly used method to compute the (2, 2) optical depth from the (1, 1) optical depth and the (2, 2) to (1, 1) main beam brightness temperature ratio leads to an underestimation of the rotational temperature and column density. A larger median virial parameter of~ 1is determined using the broaderN2H+line width than is estimated from theNH3line width of~ 0.5with a general trend of a decreasing virial parameter with increasing gas mass. We obtain a risingNH3(1, 1)/N2H+line-width ratio with increasing rotational temperature.Conclusions.A comparison ofNH3line parameters of ATLASGAL clumps to cores in nearby molecular clouds reveals smaller velocity dispersions in low-mass than high-mass star-forming regions and a warmer surrounding of ATLASGAL clumps than the surrounding of low-mass cores. TheNH3(1, 1) inversion transition of 49% of the sources shows hyperfine structure anomalies. The intensity ratio of the outer hyperfine structure lines with a median of1.27 ± 0.03and a standard deviation of 0.45 is significantly higher than 1, while the intensity ratios of the inner satellites with a median of0.9 ± 0.02and standard deviation of 0.3 and the sum of the inner and outer hyperfine components with a median of1.06 ± 0.02and standard deviation of 0.37 are closer to 1.
关键词：ensubmillimeter: ISMsurveysISM: moleculesISM: kinematics and dynamicsstars: formationstars: massive
