SRON Netherlands Institute for Space Research,
PO Box 800,
2 Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
3 Max-Planck-Institut für Radioastronomie, PO Box 20 24, 53010 Bonn, Germany
4 Univ. Bordeaux, LAB, UMR 5804, 33270 Floirac, France
5 CNRS, LAB, UMR 5804, 33270 Floirac, France
6 ASTRON Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands
Received: 31 March 2014
Accepted: 30 July 2014
Context. The earliest phases of high-mass star formation are poorly understood.
Aims. Our goal is to determine the physical conditions and kinematic structure of massive starforming cloud clumps.
Methods. We analyse H2O 557 GHz line profiles observed with HIFI toward four positions in two infrared-dark cloud clumps. By comparison with ground-based C17O, N2H+, CH3OH, and NH3 line observations, we constrain the volume density and kinetic temperature of the gas and estimate the column density and abundance of H2O and N2H+.
Results. The observed water lines are complex with emission and absorption components. The absorption is redshifted and consistent with a cold envelope, while the emission is interpreted as resulting from proto-stellar outflows. The gas density in the clumps is ~107 cm-3. The o-H2O outflow column density is 0.3−3.0 × 1014 cm-2. The o-H2O absorption column density is between 1.5 × 1014 and 2.6 × 1015 cm-2 with cold o-H2O abundances between 1.5 × 10-9 and 3.1 × 10-8.
Conclusions. All clumps have high gas densities (~107 cm-3) and display infalling gas. Three of the four clumps have outflows. The clumps form an evolutionary sequence as probed by H2O N2H+, NH3, and CH3OH. We find that G28-MM is the most evolved, followed by G11-MM and then G28-NH3. The least evolved clump is G11-NH3 which shows no signposts of starformation; G11-NH3 is a high-mass pre-stellar core.
Key words: stars: formation / stars: massive / ISM: clouds / evolution
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia with important participation of NASA.
Tables 4, 6, 8, 10, 11, and Appendix A are available in electronic form at http://www.aanda.org
Final Herschel and APEX data used in the paper (FITS files) are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (184.108.40.206) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/570/A51
© ESO, 2014