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Understanding the physics of the X-factor

Published online by Cambridge University Press:  25 November 2011

M. Röllig ,
R. Simon ,
V. Ossenkopf ,
J. Stutzki ,
S.C.O. Glover  and
M.-M. Mac Low
S.C.O. Glover
Affiliation:
Zentrum für Astronomie der Universität Heidelberg, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany
M.-M. Mac Low
Affiliation:
Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024, USA
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Abstract

We study the relationship between the H2 and CO abundances in simulated molecular clouds using a fully dynamical model of magnetized turbulence coupled to a detailed chemical network. We find that the CO-to-H2 conversion factor for a given molecular cloud, the so-called X-factor, is determined primarily by the mean extinction of the cloud, rather than by its metallicity. Our results explain the discrepancy observed in low metallicity systems between cloud masses derived from CO observations and other techniques such as infrared emission, and predict that CO-bright clouds in low metallicity systems should be systematically larger and/or denser than Milky Way clouds.

Type
Research Article
Information
European Astronomical Society Publications Series , Volume 52: Conditions and Impact of Star Formation , 2011 , pp. 147 - 150
Copyright
© EAS, EDP Sciences 2011

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