Odin observations of water in molecular outflows and shocks

TL;DR

This study uses Odin observations to measure water abundance in molecular outflows and shocks, revealing high water levels consistent with shock chemistry, but also highlighting uncertainties due to varying densities and beam effects.

Contribution

First measurement of ortho-water abundance in multiple outflows using Odin, providing insights into shock chemistry and the physical conditions of molecular outflows.

Findings

Elevated water abundances consistent with C-type shock predictions.

No correlation between water abundance and mass loss rate.

Water abundance correlates with maximum outflow velocity.

Abstract

Aims. We investigate the ortho-water abundance in outflows and shocks in order to improve our knowledge of shock chemistry and of the physics behind molecular outflows. Methods. We have used the Odin space observatory to observe the H2O(110-101) line. We obtain strip maps and single pointings of 13 outflows and two supernova remnants where we report detections for eight sources. We have used RADEX to compute the beam averaged abundances of o-H2O relative to H2. In the case of non-detection, we derive upper limits on the abundance. Results. Observations of CO emission from the literature show that the volume density of H2 can vary to a large extent, a parameter that puts severe uncertainties on the derived abundances. Our analysis shows a wide range of abundances reflecting the degree to which shock chemistry is affecting the formation and destruction of water. We also compare our results with recent results from the SWAS team. Conclusions. Elevated abundances of ortho-water are found in several sources. The abundance reaches values as high as what would be expected from a theoretical C-type shock where all oxygen, not in the form of CO, is converted to water. However, the high abundances we derive could also be due to the low densities (derived from CO observations) that we assume. The water emission may in reality stem from high density regions much smaller than the Odin beam. We do not find any relationship between the abundance and the mass loss rate. On the other hand, there is a relation between the derived water abundance and the observed maximum outflow velocity.