Astronomy and Astrophysics – Astrophysics
Scientific paper
2006-12-21
Astronomy and Astrophysics
Astrophysics
5 pages, 5 figures
Scientific paper
10.1051/0004-6361:20066184
Context: Existing SWAS observations and future HIFI/Herschel data require a clear sense of the information content of water emission and absorption lines. Aims: Investigate wether the ground-state transition of ortho-H2O, 1_(10)-1_(01), at 557GHz can be used to measure the column density throughout an interstellar cloud. Methods: We make use of a multi-zone escape probability code suitable for the treatment of molecular line emission. Results: For low abundances, i.e., X(H2O)=<10^(-9), the intensity of the 1_(10)-1_(01) transition scales with the total column of H2. However, this relationship breaks down with increasing abundance, i.e., optical depth, due to line trapping and -- for T_(dust)>=25K, X(H2O)=<10^(-8) and n~10^4 cm^(-3) -- absorption of the dust continuum. Conclusions: An observed decline in intensity per column, expected if H2O is a surface tracer, does not necessarily mean that the water is absent in the gas phase at large columns, but can be caused by line trapping and subsequent collisional de-excitation. To determine the amount of water vapour in the interstellar medium, multiple line measurements of optically thin transitions are needed to disentangle radiative transfer and local excitation effects.
Poelman D. R.
Spaans Marco
Tielens Alexander G. G. M.
No associations
LandOfFree
The interpretation of water emission from dense interstellar clouds does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with The interpretation of water emission from dense interstellar clouds, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The interpretation of water emission from dense interstellar clouds will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-21280