The physical conditions in IRDC clumps from Herschel HIFI observations of H2O
| Autor: | Shipman, Russell F., van der Tak, Floris F. S, Wyrowski, Friedrich, Herpin, Fabrice, Frieswijk, Wilfred |
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| Rok vydání: | 2014 |
| Předmět: | |
| Zdroj: | A&A 570, A51 (2014) |
| Druh dokumentu: | Working Paper |
| DOI: | 10.1051/0004-6361/201423912 |
| Popis: | 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. Comment: 15 pages, 10 figures |
| Databáze: | arXiv |
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