The physical conditions in IRDC clumps from Herschel/HIFI observations of H2O
Abstract
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.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- October 2014
- DOI:
- 10.1051/0004-6361/201423912
- arXiv:
- arXiv:1408.1515
- Bibcode:
- 2014A&A...570A..51S
- Keywords:
-
- stars: formation;
- stars: massive;
- ISM: clouds;
- evolution;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 15 pages, 10 figures