Spatial variation of the physical conditions of molecular gas in galaxies

Details Spatial variation of the physical conditions of molecular gas in galaxies Spatial variation of the physical conditions of molecular gas in galaxies

Jul 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990nascp3084..384j&link_type=abstract

In NASA, Ames Research Center, The Interstellar Medium in External Galaxies: Summaries of Contributed Papers p 384-385 (SEE N91-

Astronomy and Astrophysics

Astronomy

Carbon Monoxide, Gas Density, Isotopes, Molecular Gases, Spatial Distribution, Heating, Hydrocyanic Acid, Millimeter Waves, Optical Thickness, Radio Astronomy, Radio Receivers, Sis (Superconductors), Telescopes, Variations

Scientific paper

Multi-line studies of CO-12, CO-13, C-18O, HCN, and HCO(+) at 3 mm, 1.3 mm, and 0.8 mm using the Institute for Radio Astronomy in the Millimeter range (IRAM) 30 m telescope, with the IRAM superconductor insulator superconductor (SIS) receivers and the Max Planck Institute for External Physics (MPE) 350 GHz SIS receiver, show that the densities and temperatures of molecular gas in external galaxies change significantly with position. CO-12 measures the densities and temperature of diffuse interclump molecular gas, but not the bulk of the molecular gas. Simple one-component models, with or without external heating, cannot account for the weakness of the CO-12 J = 3 to 2 line relative to J = 2 to 1 and J = 1 to 0. CO-12 does not trace the bulk of the molecular gas, and optical depth effects obviate a straightforward interpretation of CO-12 data. Instead, researchers turned to the optically thin CO isotopes and other molecular species. Isotopic CO lines measure the bulk of the molecular gas, and HCN and HCO(+) pick out denser regions. Researchers find a warm ridge of gas in IC 342 (Eckart et al. 1989), denser gas in the starburst nucleus of IC 342, and a possible hot-spot in NGC 2903. In IC 342, NGC 2146, and NGC 6764, the CO-13 J = 2 to 1 line is subthermally populated, implying gas densities less than or equal to 104 cm(-3).

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