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Title:
CO excitation in four IR luminous galaxies
Authors:
Radford, Simon J. E.; Solomon, P. M.; Downes, Dennis
Affiliation:
AA(State Univ. of New York, Stony Brook.), AB(State Univ. of New York, Stony Brook.)
Publication:
In NASA, Ames Research Center, The Interstellar Medium in External Galaxies: Summaries of Contributed Papers p 378-380 (SEE N91-14100 05-90)
Publication Date:
07/1990
Category:
Astrophysics
Origin:
STI
NASA/STI Keywords:
ACTIVE GALAXIES, CARBON MONOXIDE, EXCITATION, FAR INFRARED RADIATION, GALACTIC RADIATION, INFRARED RADIATION, LUMINOSITY, MOLECULAR CLOUDS, MOLECULAR GASES, SPIRAL GALAXIES, STAR FORMATION, CALIBRATING, HYDROGEN, MILKY WAY GALAXY, TELESCOPES
Bibliographic Code:
1990NASCP3084..378R

Abstract

The correlation between the CO and far infrared luminosities of spiral galaxies is well established. The luminosity ration, LFIR/L sub CO in IR luminous active galaxies is, however, systematically five to ten times higher than in ordinary spirals and molecular clouds in our Galaxy. Furthermore, the masses of molecular hydrogen in luminous galaxies are large, M (H2) approx. equals 1010 solar magnitude, which indicates the observed luminosity ratios are due to an excess of infrared output, rather than a deficiency of molecular gas. These large amounts of molecular gas may fuel luminous galaxies through either star formation or nuclear activity. This interpretation rests on applying the M (H2)/LCO ratio calibrated in our Galaxy to galaxies with strikingly different luminosity ratios. But are the physical conditions of the molecular gas different in galaxies with different luminosity ratios. And, if so, does the proportionality between CO and H2 also vary among galaxies. To investigate these questions researchers observed CO (2 to 1) and (1 to 0) emission from four luminous galaxies with the Institute for Radio Astronomy in the Millimeter range (IRAM) 30 m telescope. Researchers conclude that most of the CO emission from these Arp 193, Arp 220, and Mrk 231 arises in regions with moderate ambient densities similar to the clouds in the Milky Way molecular ring. The emission is neither from dense hot cloud cores nor from the cold low density gas characteristic of the envelopes of dark clouds.
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