Volume 597, January 2017
|Number of page(s)||6|
|Section||Interstellar and circumstellar matter|
|Published online||21 December 2016|
Deuterium fractionation of a distant cold dark cloud along the line of sight of W51⋆
1 Université de Toulouse, UPS-OMP, IRAP, 31400 Toulouse, France
2 CNRS, IRAP, 9 Av. Colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
3 Tata Institute of Fundamental Research, Homi Bhabha Road, 400005 Mumbai, India
4 Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 Saint-Martin d’ Hères, France
5 LERMA, Observatoire de Paris, PSL Research University, CNRS, UMR 8112, 75014 Paris, France
6 Sorbonne Universités, UPMC Univ. Paris 06, UMR 8112, LERMA, 75005 Paris, France
Received: 11 July 2016
Accepted: 14 November 2016
Herschel/HIFI observations toward the compact HII region W51 has revealed the presence of a cold dense core along its line of sight in a high-velocity stream located just in front of W51. This detection has been made possible through absorption measurements of low-energy transitions of HDO, NH3, and C3 against the bright background emitted by the star-forming region. We present a follow-up study of this core using the high sensitivity and high spectral resolution provided by the IRAM 30m telescope. We report new detections of this core in absorption for DCO+ (2–1, 3–2), H13CO+ (1–0), DNC (3–2), HN13C (1–0), p-H2CO (20,2–10,1, 30,3–20,2), and in emission for o-NH2D. We also report interferometric observation of this last species using the IRAM/NOEMA telescope, revealing the fragmented nature of the source through the detection of two cores, separated by 0.19−0.24 pc, with average sizes of less than 0.16−0.19 pc. From a non-LTE analysis, we are able to estimate the density (~2.5 × 104 cm-3) and temperature (~10 K) of this component, typical of what is found in dark clouds. This component (called W51-core) has the same DCO+/HCO+ ratio (0.02) as TMC-1 and a high DNC/HNC ratio (0.14). Detection of these deuterated species indicates that W51-core is similar to an early-phase low-mass star-forming region, formed from the interaction between the W51 giant molecular cloud and the high-velocity stream in front of it. The W51 complex being at about 5 kpc, these findings lead to what is the first detection of the earliest phase of low-mass star-forming region at such a large distance.
Key words: astrochemistry / line: identification / molecular data / radiative transfer
IRAM 30m data are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (126.96.36.199) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/597/A45
© ESO, 2016
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