A multitransition molecular line study of inward motions towards massive star-forming cores |
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Authors: | Yan Sun Yu Gao |
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Institution: | Purple Mountain Observatory, Chinese Academy of Sciences, 2 West Beijing Road, Nanjing, Jiangsu 210008, China;Graduate School of the Chinese Academy of Sciences, Beijing 100080, China |
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Abstract: | A multitransition 3-mm molecular line single pointing and mapping survey was carried out towards 29 massive star-forming cores in order to search for the signature of inward motions. Up to seven different transitions, optically thick lines HCO+(1-0), CS(2-1), HNC(1-0), HCN(1-0) and 12CO(1-0), and optically thin lines C18O(1-0) and 13CO(1-0) were observed towards each source. The normalized velocity differences ( ) between the peak velocities of optically thick lines and optically thin line C18O(1-0) for each source were derived. Prominent inward motions are probably present in either HCO+(1-0) or CS(2-1) or HNC(1-0) observations in most sources. Our observations show that there is a significant difference in the incidence of blueshifted asymmetric line profiles between CS(2-1) and HCO+(1-0). The HCO+(1-0) shows the highest occurrence of obvious asymmetric features, perhaps owing to different optical depth between CS(2-1) and HCO+(1-0). HCO+(1-0) appears to be the best inward motion tracer. The mapping observations of multiple line transitions enable us to identify six strong infall candidates: G123.07-6.31, W75(OH), S235N, CEP-A, W3(OH) and NGC 7538. The infall signature is extended up to a linear scale >0.2 pc . |
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Keywords: | stars: formation ISM: kinematics and dynamics ISM: molecules radio lines: ISM |
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