Reversal of infall in SgrB2(M) revealed by Herschel/HIFI observations of HCN lines at THz frequencies
Rolffs, R. and Schilke, P. and Comito, C. and Bergin, E.A. and van der Tak, F.F.S. and Lis, D.C. and Qin, S.-L. and Menten, K.M. and Gusten, R. and Bell, T.A. and Blake, G.A. and Caux, E. and Ceccarelli, C. and Cernicharo, J. and Crockett, N.R. and Daniel, F. and Dubernet, M.-L. and Emprechtinger, M. and Encrenaz, P. and Gerin, M. and Giesen, T.F. and Goicoechea, J.R. and Goldsmith, P.F. and Gupta, H. and Herbst, E. and Joblin, C. and Johnstone, D. and Langer, W.D. and Latter, W.D. and Lord, S.D. and Maret, S. and Martin, P.G. and Melnick, G.J. and Morris, P. and Muller, H.S.P. and Murphy, J.A. and Ossenkopf, V. and Pearson, J.C. and Perault, M. and Phillips , T.G. and Plume, R. and Schlemmer, S. and Stutzki, J. and Trappe, N. and Vastel, C. and Wang, S. and Yorke, H.W. and Yu, S. and Zmuidzinas, J. and Diez-Gonzalez, C. and Bachiller, R. and Martin-Pintado, J. and Baechtold, W. and Olberg, M. and Nordh, L.H. and Gill, J.J. and Chattopadhyay, G. (2010) Reversal of infall in SgrB2(M) revealed by Herschel/HIFI observations of HCN lines at THz frequencies. Astronomy & Astrophysics, 521 (L46). pp. 1-5. ISSN 0004-6361
Aims. To investigate the accretion and feedback processes in massive star formation, we analyze the shapes of emission lines from hot molecular cores, whose asymmetries trace infall and expansion motions. Methods. The high-mass star forming region SgrB2(M) was observed with Herschel/HIFI (HEXOS key project) in various lines of HCN and its isotopologues, complemented by APEX data. The observations are compared to spherically symmetric, centrally heated models with density power-law gradient and different velocity fields (infall or infall+expansion), using the radiative transfer code RATRAN. Results. The HCN line profiles are asymmetric, with the emission peak shifting from blue to red with increasing J and decreasing line opacity (HCN to H13CN). This is most evident in the HCN 12–11 line at 1062 GHz. These line shapes are reproduced by a model whose velocity field changes from infall in the outer part to expansion in the inner part. Conclusions. The qualitative reproduction of the HCN lines suggests that infall dominates in the colder, outer regions, but expansion dominates in the warmer, inner regions. We are thus witnessing the onset of feedback in massive star formation, starting to reverse the infall and finally disrupting the whole molecular cloud. To obtain our result, the THz lines uniquely covered by HIFI were critically important.
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