Mon. Not. R. Astron. Soc., 473, 271-285 (2018/January-1)
CO line emission from galaxies in the Epoch of Reionization.
VALLINI L., PALLOTTINI A., FERRARA A., GALLERANI S., SOBACCHI E. and BEHRENS C.
Abstract (from CDS):
We study the CO line luminosity (LCO), the shape of the CO spectral line energy distribution (SLED), and the value of the CO-to-H2 conversion factor in galaxies in the Epoch of Reionization (EoR). For this aim, we construct a model that simultaneously takes into account the radiative transfer and the clumpy structure of giant molecular clouds (GMCs) where the CO lines are excited. We then use it to post-process state-of-the-art zoomed, high resolution (30 pc), cosmological simulation of a main-sequence (M* ≃ 1010 M☉, SFR ≃ 100 M☉ yr^- 1^) galaxy, 'Althaea', at z ≃ 6. We find that the CO emission traces the inner molecular disc (r ≃ 0.5 kpc) of Althaea with the peak of the CO surface brightness co-located with that of the [C II] 158 µm emission. Its LCO(1–0) = 104.85 L☉ is comparable to that observed in local galaxies with similar stellar mass. The high (Σgas ≃ 220 M☉ pc^- 2^) gas surface density in Althaea, its large Mach number ( M ≃ 30) and the warm kinetic temperature (Tk ≃ 45 K) of GMCs yield a CO SLED peaked at the CO(7-6) transition, i.e. at relatively high-J and a CO-to-H2 conversion factor α_ CO_~1.5 M☉ (K km s–1 pc2)-1^ lower than that of the Milky Way. The Atacama Large Millimeter/submillimeter Array observing time required to detect (resolve) at 5σ the CO(7-6) line from galaxies similar to Althaea is ≃13 h (≃38 h).
© 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
ISM: clouds - ISM: molecules - galaxies: high-redshift - galaxies: ISM - infrared: ISM - infrared: ISM
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