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Observations of the CO J=6-5 transition in starburst galaxiesOver the past several years, short-submillimeter observations of carbon monoxide's (CO) mid-J rotational levels have revealed the presence of a large amount of excited molecular gas in luminous giant molecular clouds in our Galaxy. Submillimeter lines are specific probes of excited material: collisional excitation of the level energy of 116 K above ground, and 6-5 transition's critical density is approximately 10(exp 6) cm(exp -3) in optically thin gas. Radiative trapping effects reduce the excitation requirements to some extent, but detection of the CO J=6-5 line is nearly indisputable proof of the existence of gas that is both warm and dense. The excitation conditions also imply that cool (T less than 20 K) molecular clouds within the beam neither emit nor absorb in the short-submillimeter lines; in our Galaxy, clouds with active massive star formation emit the strongest short-submillimeter CO rotational lines. We used these properties to explore the distribution of excited molecular material and physical conditions within the star formation regions of several classical starburst nuclei: NGC253, M82, and IC342. We have used the 6-5 transition as a thermometer of warm molecular gas in starburst nuclei, unambiguously finding that the nuclear molecular gas in starburst galaxies is substantially warmer than in typical disk clouds.
Document ID
19930017594
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Harris, A. I. (Hawaii Univ. Hilo., United States)
Hills, R. E. (Cambridge Univ. United Kingdom)
Stutzki, J. (Cologne Univ. Germany)
Graf, U. U. (Texas Univ. Austin., United States)
Russell, A. P. G. (Royal Observatory Edinburgh, United Kingdom)
Tacconi, L. J. (Hawaii Univ. Hilo., United States)
Genzel, R. (Hawaii Univ. Hilo., United States)
Date Acquired
September 6, 2013
Publication Date
January 1, 1993
Publication Information
Publication: NASA. Ames Research Center, The Evolution of Galaxies and Their Environment
Subject Category
Astrophysics
Accession Number
93N26783
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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IDRelationTitle19930017517Collected WorksThe Evolution of Galaxies and Their Environment
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