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Synthetic [C ii] emission maps of a simulated molecular cloud in formation

Franeck, A., Walch, S., Seifried, D., Clarke, S., Ossenkopf-Okada, V., Glover, S.C.O., Klessen, R.S., Girichidis, P., Naab, T., Wunsch, R., Clark, Paul, Pellegrini, E. and Peters, T. 2018. Synthetic [C ii] emission maps of a simulated molecular cloud in formation. Monthly Notices of the Royal Astronomical Society 481 (4) , pp. 4277-4299. 10.1093/mnras/sty2507

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Abstract

The C+ ion is an important coolant of interstellar gas, and so the [C ii] fine structure line is frequently observed in the interstellar medium. However, the physical and chemical properties of the [C ii]-emitting gas are still unclear. We carry out non-LTE radiative transfer simulations with radmc–3d to study the [C ii] line emission from a young, turbulent molecular cloud before the onset of star formation, using data from the SILCC-Zoom project. The [C ii] emission is optically thick over 40% of the observable area with I[CII] > 0.5 K km s−1. To determine the physical properties of the [C ii] emitting gas, we treat the [C ii] emission as optically thin. We find that the [C ii] emission originates primarily from cold, moderate density gas (40 ≲ T ≲ 65 K and 50 ≲ n ≲ 440 cm−3), composed mainly of atomic hydrogen and with an effective visual extinction between ∼0.50 and ∼0.91. Gas dominated by molecular hydrogen contributes only ≲20% of the total [C ii] line emission. Thus, [C ii] is not a good tracer for CO-dark H2 at this early phase in the cloud’s lifetime. We also find that the total gas, H and C+ column densities are all correlated with the integrated [C ii] line emission, with power law slopes ranging from 0.5 to 0.7. Further, the median ratio between the total column density and the [C ii] line emission is YCII ≈ 1.1 × 1021 cm−2 (K km s−1)−1, and YCII scales with I −0.3 [CII] I[CII]−0.3 . We expect YCII to change in environments with a lower or higher radiation field than simulated here.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Publisher: Oxford University Press
ISSN: 0035-8711
Date of First Compliant Deposit: 3 October 2018
Date of Acceptance: 11 September 2018
Last Modified: 20 Sep 2019 10:10
URI: http://orca.cf.ac.uk/id/eprint/115491

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