Letter to the Editor

Submillimeter emission from water in the W3 region ^*

¹ Department of Physics & Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada
² Onsala Space Observatory, 439 92 Onsala, Sweden
³ CESR, 9 avenue du Colonel Roche, BP 4346, 31029 Toulouse, France
⁴ Laboratoire d'Astronomie Spatiale, BP 8, 13376 Marseille Cedex 12, France
⁵ Department of Physics, University of Waterloo, Waterloo, ON N2L 3G1, Canada
⁶ LERMA & FRE du CNRS, Observatoire de Paris, 61 Av. de l'Observatoire, 75140 Paris, France
⁷ LERMA & FRE 2460 du CNRS, École Normale Supérieure, 24 rue Lhomond, 75005 Paris, France
⁸ Herzberg Institute of Astrophysics, National Research Council, 5071 West Saanich Road, Victoria, BC V8X 4M6, Canada
⁹ Stockholm Observatory, SCFAB, Roslagstullsbacken 21, 106 91 Stockholm, Sweden
¹⁰ Swedish Space Corporation, PO Box 4207, 171 04 Solna, Sweden
¹¹ Observatory, PO Box 14, University of Helsinki, 00014 Helsinki, Finland
¹² Department of Physics and Astronomy, University of Calgary, Calgary, AB T2N 1N4, Canada
¹³ LESIA, Observatoire de Paris, Section de Meudon, 5 place Jules Janssen, 92195 Meudon Cedex, France
¹⁴ Metsahovi Radio Observatory, Helsinki University of Technology, Otakaari 5A, 02150 Espoo, Finland
¹⁵ Department of Astronomy and Physics, Saint Mary's University, Halifax, Nova Scotia B3H 3C3, Canada
¹⁶ Swedish National Space Board, Box 4006, 171 04 Solna, Sweden

Corresponding author: C. D. Wilson, wilson@physics.mcmaster.ca

Received: 29 November 2002
Accepted: 29 January 2003

Abstract

Using the Odin satellite, we have mapped the submillimeter emission from the transition of ortho-water in the W3 star-forming region. A map of the W3 IRS4 and W3 IRS5 region reveals strong water lines at half the positions in the map. The relative strength of the Odin lines compared to previous observations by SWAS suggests that we are seeing water emission from an extended region. Across much of the map the lines are double-peaked, with an absorption feature at –39 km s^-1; however, some positions in the map show a single strong line at –43 km s^-1. We interpret the double-peaked lines as arising from optically thick, self-absorbed water emission near the W3 IRS5, while the narrower blue-shifted lines originate in emission near W3 IRS4. In this model, the unusual appearance of the spectral lines across the map results from a coincidental agreement in velocity between the emission near W3 IRS4 and the blue peak of the more complex lines near W3 IRS5. The strength of the water lines near W3 IRS4 suggests we may be seeing water emission enhanced in a photon-dominated region.