# Direct Observation of a Sharp Transition to Coherence in Dense Cores

 Title: Direct Observation of a Sharp Transition to Coherence in Dense Cores Author: Pineda, Jaime Eduardo; Goodman, Alyssa A.; Caselli, Paola; Foster, Jonathan B.; Myers, Philip C.; Rosolowsky, Erik W.; Arce, Hector G. Note: Order does not necessarily reflect citation order of authors. Citation: Jaime, E. Pineda, Alyssa A. Goodman, Hector G. Arce, Paola Caselli, Jonathan B. Foster, Philip C. Myers, and Erik W. Rosolowsky. 2010. Direct observation of a sharp transition to coherence in dense cores. The Astrophysical Journal Letters 712(1): L116-L121. Full Text & Related Files: Goodman_DirectObservation.pdf (631.1Kb; PDF) Abstract: We present $$NH_3$$ observations of the B5 region in Perseus obtained with the Green Bank Telescope. The map covers a region large enough $$(\sim 11'×14')$$ that it contains the entire dense core observed in previous dust continuum surveys. The dense gas traced by $$NH_{3}(1,1)$$ covers a much larger area than the dust continuum features found in bolometer observations. The velocity dispersion in the central region of the core is small, presenting subsonic non-thermal motions which are independent of scale. However, it is because of the coverage and high sensitivity of the observations that we present the detection, for the first time, of the transition between the coherent core and the dense but more turbulent gas surrounding it. This transition is sharp, increasing the velocity dispersion by a factor of 2 in less than 0.04 pc (the 31'' beam size at the distance of Perseus,$$\sim 250 pc)$$. The change in velocity dispersion at the transition is $$\approx 3 km \ s^{-1} \ pc^{–1}$$. The existence of the transition provides a natural definition of dense core: the region with nearly constant subsonic non-thermal velocity dispersion. From the analysis presented here, we can neither confirm nor rule out a corresponding sharp density transition. Published Version: doi:10.1088/2041-8205/712/1/L116 Other Sources: http://arxiv.org/abs/1002.2946v1 Terms of Use: This article is made available under the terms and conditions applicable to Open Access Policy Articles, as set forth at http://nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of-use#OAP Citable link to this page: http://nrs.harvard.edu/urn-3:HUL.InstRepos:4706182

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