2016MNRAS.456.3596G -
Mon. Not. R. Astron. Soc., 456, 3596-3609 (2016/March-2)
Is atomic carbon a good tracer of molecular gas in metal-poor galaxies?
GLOVER S.C.O. and CLARK P.C.
Abstract (from CDS):
Carbon monoxide (CO) is widely used as a tracer of molecular hydrogen (H2) in metal-rich galaxies, but is known to become ineffective in low-metallicity dwarf galaxies. Atomic carbon has been suggested as a superior tracer of H2 in these metal-poor systems, but its suitability remains unproven. To help us to assess how well atomic carbon traces H2 at low metallicity, we have performed a series of numerical simulations of turbulent molecular clouds that cover a wide range of different metallicities. Our simulations demonstrate that in star-forming clouds, the conversion factor between [Ci] emission and H2 mass, XCI, scales approximately as XCI ∝ Z-1. We recover a similar scaling for the CO-to-H2 conversion factor, XCO, but find that at this point in the evolution of the clouds, XCO is consistently smaller than XCI, by a factor of a few or more. We have also examined how XCI and XCO evolve with time. We find that XCI does not vary strongly with time, demonstrating that atomic carbon remains a good tracer of H2 in metal-poor systems even at times significantly before the onset of star formation. On the other hand, XCO varies very strongly with time in metal-poor clouds, showing that CO does not trace H2 well in starless clouds at low metallicity.
Abstract Copyright:
© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society (2016)
Journal keyword(s):
stars: formation - ISM: clouds - ISM: molecules - galaxies: ISM
Simbad objects:
3
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