Distribution of water in the G327.3–0.6 massive star-forming region^⋆

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: sleurini@mpifr-bonn.mpg.de
² INAF – Osservatorio Astronomico di Cagliari, via della Scienza 5, 09047 Selargius (CA), Italy
³ Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
⁴ SRON Netherlands Institute for Space Research, PO Box 800, 9700 AV Groningen, The Netherlands
⁵ Kapteyn Astronomical Institute, University of Groningen, 9712 Groningen, The Netherlands
⁶ Kavli Institut for Astronomy and Astrophysics, Yi He Yuan Lu 5, HaiDian Qu, Peking University, 100871 Beijing, PR China
⁷ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁸ Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany

Received: 2 January 2017
Accepted: 17 March 2017

Abstract

Aims. Following our past study of the distribution of warm gas in the G327.3–0.6 massive star-forming region, we aim here at characterizing the large-scale distribution of water in this active region of massive star formation made of individual objects in different evolutionary phases. We investigate possible variations of the water abundance as a function of evolution.

Methods. We present Herschel/PACS (4′× 4′) continuum maps at 89 and179 μm encompassing the whole region (Hii region and the infrared dark cloud, IRDC) and an APEX/SABOCA (2′× 2′) map at 350 μm of the IRDC. New spectral Herschel/HIFI maps toward the IRDC region covering the low-energy water lines at 987 and 1113 GHz (and their H₂¹⁸O counterparts) are also presented and combined with HIFI pointed observations toward the G327 hot core region. We infer the physical properties of the gas through optical depth analysis and radiative transfer modeling of the HIFI lines.

Results. The distribution of the continuum emission at 89 and 179 μm follows the thermal continuum emission observed at longer wavelengths, with a peak at the position of the hot core and a secondary peak in the Hii region, and an arch-like layer of hot gas west of this Hii region. The same morphology is observed in the p-H₂O 1₁₁–0₀₀ line, in absorption toward all submillimeter dust condensations. Optical depths of approximately 80 and 15 are estimated and correspond to column densities of 10¹⁵ and 2 × 10¹⁴ cm^-2, respectively, for the hot core and IRDC position. These values indicate an abundance of water relative to H₂ of 3 × 10^-8 toward the hot core, while the abundance of water does not change along the IRDC with values close to some 10^-8. Infall (over at least 20″) is detected toward the hot core position with a rate of 1−1.3 × 10^-2M_⊙ /yr, high enough to overcome the radiation pressure that is due to the stellar luminosity. The source structure of the hot core region appears complex, with a cold outer gas envelope in expansion, situated between the outflow and the observer, extending over 0.32 pc. The outflow is seen face-on and rather centered away from the hot core.

Conclusions. The distribution of water along the IRDC is roughly constant with an abundance peak in the more evolved object, that is, in the hot core. These water abundances are in agreement with previous studies in other massive objects and chemical models.