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First detection of extragalactic 13CO(6-5) line emission

Published online by Cambridge University Press:  04 October 2008

C. Kramer ,
S. Aalto ,
R. Simon ,
G.J. Stacey ,
S. Hailey-Dunsheath ,
T. Nikola ,
T.E. Oberst ,
S.C. Parshley  and
C.M. Bradford
G.J. Stacey*
Affiliation:
Cornell University, Ithaca, NY 14853, USA
S. Hailey-Dunsheath
Affiliation:
Cornell University, Ithaca, NY 14853, USA
T. Nikola
Affiliation:
Cornell University, Ithaca, NY 14853, USA
T.E. Oberst
Affiliation:
Cornell University, Ithaca, NY 14853, USA
S.C. Parshley
Affiliation:
Cornell University, Ithaca, NY 14853, USA
C.M. Bradford
Affiliation:
Jet Propulsion Lab.
*
gjs12@cornell.edu
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Abstract

We report the first detection of a mid-J isotopic CO line from an external galaxy. We detected the 13CO (6-5) line from the starburst nucleus of NGC 253. The line is suprisingly bright with an integrated intensity 7% of the 12CO (6-5) line, indicating optical depth in the 12CO line. Our LVG modeling shows that a single warm(T ~ 120 K), dense (n ~ 104cm-3) component emits most of the 12CO and 13CO line emission from J = 2-1 through J = 7-6. The CO(1-0) line comes from an additional lower excitation envelope. About 60% of the total molecular gas mass within 70 pc of the nucleus is in the warm, dense component. We show that stellar far-UV photons or X-ray photons from a nuclear source are unlikely to be the primary sources of the gas heating. The most likely sources of heat are cosmic rays from the nuclear starburst or microturbulence within molecular clouds.


Type
Research Article
Information
European Astronomical Society Publications Series , Volume 31: Far-Infrared Workshop 2007 , 2008 , pp. 151 - 154
Copyright
© EAS, EDP Sciences, 2008

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