Understanding the physics of the X-factor

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.

To appear in "Conditions and impact of star formation: New results with Herschel and beyond", Proceedings of the 5th Zermatt ISM symposium. 4 pages, 1 figure

References in corpus (4)

• The Resolved Properties of Extragalactic Giant Molecular Clouds
• CO Isotopologues in the Perseus Molecular Cloud Complex: the X-Factor and Regional Variations
• Giant Molecular Clouds in M33 -- II. High Resolution Observations
• The Structure of a Low-Metallicity Giant Molecular Cloud Complex

Cited by in corpus (3)

• Herschel Exploitation of Local Galaxy Andromeda (HELGA) III: The Star Formation Law in M31
• Disentangling the ISM phases of the dwarf galaxy NGC 4214 using [CII] SOFIA/GREAT observations
• $\text{slick}$: Modeling a Universe of Molecular Line Luminosities in Hydrodynamical Simulations