Deuterium fractionation of a distant cold dark cloud along the line of sight of W51

Abstract

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 30-meter 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 (202-101, 303-202), 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 (~2.5e4 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.

6 pages, 2 figures, accepted in Astronomy & Astrophysics

References in corpus (6)

• Isotopic fractionation of carbon, deuterium and nitrogen : a full chemical study
• The Distribution of Ortho-H_2D+(1_1,0 - 1_1,1) in L1544: Tracing the Deuteration Factory in Prestellar Cores
• Investigating the structure and fragmentation of a highly filamentary IRDC
• Fragmentation and Kinematics of dense molecular cores in the filamentary infrared-dark cloud G011.11-0.12
• ALMA Observations of the IRDC Clump G34.43+00.24 MM3: DNC/HNC Ratio
• Detection of a dense clump in a filament interacting with W51e2

Cited by in corpus (4)

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• Deuterium Chemistry in the Young Massive Protostellar Core NGC 2264 CMM3
• The Cygnus Allscale Survey of Chemistry and Dynamical Environments: CASCADE III. The large scale distribution of DCO+, DNC and DCN in the DR21 filament