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The CO Luminosity - H2 Mass Conversion Factor

Published online by Cambridge University Press:  03 August 2017

P. M. Solomon  and
J.W. Barrett
P. M. Solomon
Affiliation:
Astronomy Program, SUNY, Stony Brook, New York 11794, USA
J.W. Barrett
Affiliation:
Astronomy Program, SUNY, Stony Brook, New York 11794, USA

Abstract

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The use of 12CO as a mass tracer of H2 in molecular clouds is based on three independent calibrations, all of which agree. The physical basis for an approximately constant molecular (H2) mass to CO luminosity ratio is the origin of the CO emission from gravitationally bound molecular clouds. We discuss the size-line width and virial mass-CO luminosity relations derived from the Massachusetts-Stony Brook CO Survey. The criticisms of the size-line width relation by the Wolfendale group are wrong. Their tests were not self consistent, and were constrained by the properties of the real clouds, not independent of them, as was implied. We show that the virial masses are a reliable measure of the true cloud masses. The CO to H2 conversion factor depends only weakly on molecular cloud parameters, and its value in other spiral galaxies should not be very different from that in the Milky Way. The H2 masses in the centers of galaxies are not overestimated, since the CO excitation is observed to be normal there, and the brightness temperatures not much different from those in the Milky Way. The effect of metallicity on the conversion factor is also briefly discussed.

Type
Panel Discussion
Information
Symposium - International Astronomical Union , Volume 146: Dynamics of Galaxies and their Molecular Cloud Distributions , 1991 , pp. 235 - 241
Copyright
Copyright © Kluwer 1991 

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