Physical properties of outflows Comparing CO- and H2O-based parameters in Class 0 sources

Journal article, 2013

Context. The observed physical properties of outflows from low-mass sources put constraints on possible ejection mechanisms. Historically, these quantities have been derived from CO using ground-based observations. It is, therefore, important to investigate whether parameters such as momentum rate (thrust) and mechanical luminosity (power) are the same when different molecular tracers are used. Aims. Our objective is to determine the outflow momentum, dynamical time-scale, thrust, energy, and power using CO and H2O as tracers of outflow activity. Methods. Within the framework of the Water In Star-forming regions with Herschel (WISH) key program, three molecular outflows from Class 0 sources have been mapped using the Heterodyne Instrument for the Far Infrared (HIFI) instrument aboard Herschel. We used these observations together with previously published H-2 data to infer the physical properties of the outflows. We compared the physical properties derived here with previous estimates based on CO observations. Results. Inspection of the spatial distribution of H2O and H-2 confirms that these molecules are co-spatial. The most prominent emission peaks in H-2 coincide with strong H2O emission peaks and the estimated widths of the flows when using the two tracers are comparable. Conclusions. For the momentum rate and the mechanical luminosity, inferred values are not dependent on which tracer is used, i.e. the values agree to within a factor of 4 and 3, respectively.