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New Conversion Laws for CO Observations

Published online by Cambridge University Press:  21 March 2017

Peter J. Barnes ,
Erik Muller ,
Audra K. Hernandez ,
Ana Duarte-Cabral  and
Frederic Schuller
Peter J. Barnes
Affiliation:
Astronomy Dept., University of Florida, PO Box 112055, Gainesville FL 32611, USA School of Science & Technology, University of New England, Armidale NSW 2351, Australia
Erik Muller
Affiliation:
National Astronomical Observatory of Japan, Chile Observatory, Tokyo 181-8588, Japan
Audra K. Hernandez
Affiliation:
Astronomy Dept., University of Wisconsin, 475 North Charter St., Madison, WI 53706, USA
Ana Duarte-Cabral
Affiliation:
School of Physics, University of Exeter, Stocker Road, Exeter, EX4 4QL, United Kingdom
Frederic Schuller
Affiliation:
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121, Bonn, Germany email: [email protected], [email protected], [email protected]
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Abstract

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We describe new conversion laws, from CO molecular line data to inferred mass column, based on observations of the three main CO isotopologues in several surveys of the Galactic Plane. The new conversion laws replace the use of the single “X-factor” in widespread use, with a more physically-based relationship between the CO line’s optical depth, excitation, and column density. It has the effect of increasing the inferred mass column, over the single X-factor, by typically a factor of 2–3. This means that the molecular mass of the Milky Way may have been substantially underestimated in previous studies, and suggests that scaling laws like the Kennicutt-Schmidt relations may also need to be recalibrated. Because of its statistical basis on a large fraction of our Galaxy’s ISM, this new law is also recommended for use in studies of other Milky-Way-analogue spiral galaxies.

Keywords

galaxies: abundancesISM: moleculesastrochemistry
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 11 , Symposium S321: Formation and Evolution of Galaxy Outskirts , March 2016 , pp. 270 - 271
Copyright
Copyright © International Astronomical Union 2017 

References

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