The physical conditions in IRDC clumps from Herschel HIFI observations of H2O

• Published in: arXiv.org 2014-08
• Main Authors: Shipman, Russell F, Floris F S van der Tak, Wyrowski, Friedrich, Herpin, Fabrice, Frieswijk, Wilfred
• Format: Article
• Language: English
• Subjects: Absorption; Ammonia; Clumps; Emission; Gas density; Massive stars; Outflow; Protostars; Space telescopes; Star & galaxy formation; Star formation; Stellar evolution
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1408.1515

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 star-forming cloud clumps. Methods. We analyze H\(_2\)O 557 GHz line profiles observed with HIFI toward four positions in two infrared-dark cloud clumps . By comparison with ground-based C\(^{17}\)O, N\(_2\)H\(^+\), CH\(_3\)OH and NH\(_3\) line observations, we constrain the volume density and kinetic temperature of the gas and estimate the column density and abundance of H\(_2\)O and N\(_2\)H\(^+\). Results. The observed water lines are complex with emission and absorption components. The absorption is red shifted and consistent with a cold envelope, while the emission is interpreted as resulting from protostellar outflows. The gas density in the clumps is \(\sim\) 10\(^7\) cm\(^{-3}\). The o-H2O outflow column density is 0.3 to 3.0 10\(^{14}\) cm\(^{-2}\), the o-H2O absorption column density is between 1.5 10\(^{14}\) and 2.6 10\(^{15}\) cm\(^-2\) with cold o-H2O abundances between 1.5 10\(^{-9}\) and 3.1 10\(^{-8}\). Conclusions. All clumps have high gas densities (\(\sim\) 10\(^7\) cm\(^{-3}\)) and display infalling gas. Three of the four clumps have outflows. The clumps form an evolutionary sequence as probed by H\(_2\)O N\(_2\)H\(^+\), NH\(_3\) and CH\(_3\)OH. We find that G28-MM is the most evolved, followed by G11-MM then G28-NH3. The least evolved clump is G11-NH3 which shows no sign-posts of star-formation. G11-NH3 is a high-mass pre-stellar core.