Physical properties of outflows^⋆

Comparing CO- and H₂O-based parameters in Class 0 sources

¹ Department of Earth and Space SciencesChalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
e-mail: per.bjerkeli@chalmers.se
² INAF – Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Italy
³ Observatorio Astronómico Nacional (IGN), Calle Alfonso XII, 3., 28014 Madrid, Spain
⁴ Onsala Space Observatory, Chalmers University of Technology, 439 92 Onsala, Sweden
⁵ Harvard–Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

Received: 30 January 2013
Accepted: 7 March 2013

Abstract

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 H₂ 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 H₂ confirms that these molecules are co-spatial. The most prominent emission peaks in H₂ 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.