Volume 579, July 2015
|Number of page(s)||35|
|Section||Galactic structure, stellar clusters and populations|
|Published online||03 July 2015|
1 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
2 Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5, 50125 Firenze, Italy
3 Dublin Institute of Advanced Studies, Fitzwilliam Place 31, Dublin 2, Ireland
4 Université de Bordeaux, Laboratoire d’Astrophysique de Bordeaux, CNRS/INSU, UMR 5804, BP 89, 33271 Floirac Cedex, France
5 Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille), UMR 7326, 13388 Marseille, France
6 Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
7 Australia Telescope National Facility, CSIRO, PO Box 76, Epping, NSW 1710, Australia
8 Alonso de Cordova 3107, Casilla 19001, Santiago 19, Chile
Received: 13 August 2014
Accepted: 5 February 2015
Context. The formation of high mass stars and clusters occurs in giant molecular clouds. Objects in evolved stages of massive star formation such as protostars, hot molecular cores, and ultracompact HII regions have been studied in more detail than earlier, colder objects. Further progress thus requires the analysis of the time before massive protostellar objects can be probed by their infrared emission. With this in mind, the APEX Telescope Large Area Survey of the whole inner Galactic plane at 870 μm (ATLASGAL) has been carried out to provide a global view of cold dust and star formation at submillimetre wavelengths.
Aims. We derive kinematic distances to a large sample of massive cold dust clumps from their measured line velocities. We estimate masses and sizes of ATLASGAL sources, for which the kinematic distance ambiguity is resolved.
Methods. The ATLASGAL sample is divided into groups of sources, which are located close together, mostly within a radius of 2 pc, and have velocities in a similar range with a median velocity dispersion of ~1 km s-1. We use NH3, N2H+, and CS velocities to calculate near and far kinematic distances to those groups.
Results. We obtain 296 groups of ATLASGAL sources in the first quadrant and 393 groups in the fourth quadrant, which are coherent in space and velocity. We analyse HI self-absorption and HI absorption to resolve the kinematic distance ambiguity to 689 complexes of submm clumps. They are associated with 12CO emission probing large-scale structure and 13CO (1–0) line as well as the 870 μm dust continuum on a smaller scale. We obtain a scale height of ~28 ± 2 pc and displacement below the Galactic midplane of ~−7 ± 1 pc. Within distances from 2 to 18 kpc ATLASGAL clumps have a broad range of gas masses with a median of 1050 M⊙ as well as a wide distribution of radii with a median of 0.4 pc. Their distribution in galactocentric radii is correlated with spiral arms.
Conclusions. Using a statistically significant ATLASGAL sample we derive a power-law exponent of −2.2 ± 0.1 of the clump mass function. This is consistent with the slope derived for clusters and with that of the stellar initial mass function. Examining the power-law index for different galactocentric distances and various source samples shows that it is independent of environment and evolutionary phase. Fitting the mass-size relationship by a power law gives a slope of 1.76 ± 0.01 for cold sources such as IRDCs and warm clumps associated with HII regions.
Key words: surveys / submillimeter: general / radio lines: ISM / ISM: molecules / ISM: kinematics and dynamics / stars: formation
Appendices are available in electronic form at http://www.aanda.org
Full Tables 2 and 3 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (18.104.22.168) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/579/A91
© ESO, 2015
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