First Observations of extragalactic CSJ = 1 goes to 0

Details First Observations of extragalactic CSJ = 1 goes to 0 First Observations of extragalactic CSJ = 1 goes to 0

Apr 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995aj....109.1716p&link_type=abstract

Astronomical Journal (ISSN 0004-6256), vol. 109, no. 4, p. 1716-1723

Other

17

Carbon Compounds, Emission Spectra, Galactic Structure, Hydrocyanic Acid, Interstellar Gas, Maffei Galaxies, Molecular Clouds, Astronomical Models, Astronomical Observatories

Scientific paper

We report the first detection of extragalactic CSJ = 1 goes to 0 emission. Because CS requires relatively high densities for thermal excitation (nH2 greater than or approximately equal to 104/cu cm), CS emission is expexcted from the denser core regions of molecular clouds. Using the Nobeyama 45m telescope, we detected unresolved CSJ = 1 goes to 0 emission from Maffei 2 and M51. The Cs J = 1 goes to 0 line was also detected from NGC 253 with the Nobeyama millimeter Array, and CSJ = 3 goes to 2 emission was mapped along the major axis of NGC 253 with the IRAM 30m. Analysis of a single gas component CS excitation model implies that the cloud properties in these galaxies are very similar to those derived from similar CO studies, even though the critical density of a given line of CS is approximately 25 times higher. On the other hand, the cloud properties derived from CS studies are different from those derived from HCN, whose lines have critical densities approximately 13 times those of CS. The CSJ = 1 goes to 0 emission than with that of HCN. From theroretical CO/CS and HCN/CSJ = 1 goes to 0 line ratio calculations, we find that the observed HCN is concentrated in smaller regions than the more diffuse gas traced by CS and CO. Model calculations suggest that the total beam-averaged ccolumn density of H2 traced by CO is greater than that traced by CS, which in turn is greater than the column density traced by HCN. Therefore, because CO, CS, and HCN apparently trace different physical regions in these galaxies, a single-component, uniform cloud model cannot simultaneously account for emission from species with different critical densities.

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