First measurements of extragalactic CO(4-3)

Details First measurements of extragalactic CO(4-3) First measurements of extragalactic CO(4-3)

Jan 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993apj...402..537g&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 402, no. 2, p. 537-545.

Astronomy and Astrophysics

Astrophysics

84

Carbon Monoxide, Galactic Nuclei, Interstellar Matter, Molecular Clouds, Molecular Gases, Brightness Temperature, Interstellar Gas, Molecular Excitation, Star Formation

Scientific paper

The first measurements of extragalactic CO(4-3) toward a sample of prominent nearby galactic nuclei (NGC 253, IC 342, M82, and NGC 6946) are reported. Detection of the CO(4-3) line provides direct evidence for large amounts of warm dense molecular gas. A multitransition CO excitation analysis, based on all presently observed (C-12)O and (C-13)O transitions up to J = 6-5 was performed to confine the physical state of the gas. Single-component homogeneous models fail to fit the observations. Toward IC 342, the present excitation study determines the average properties of the massive molecular clouds and the more extensive 'intercloud' medium seen in recent interferometric maps. The massive clouds are dense and warm, resembling those in the center of the Galaxy. While the highly excited gas phase in M82 (and NGC 253) is likely related to nuclear star formation activity and concomitant high UV flux, for the more moderate excitation conditions in IC 342 (and NGC 6946), large-scale heating processes, such as the dissipation of turbulence, may be viable.

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