Volume 631, November 2019
|Number of page(s)||6|
|Section||Letters to the Editor|
|Published online||14 November 2019|
Letter to the Editor
First detection of [13C II] in the Large Magellanic Cloud
I. Physikalisches Institut der Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany
Accepted: 22 October 2019
Context. [13C II] observations in several Galactic sources show that the fine-structure [12C II] emission is often optically thick (the optical depths around 1 to a few).
Aims. Our goal was to test whether this also affects the [12C II] emission from nearby galaxies like the Large Magellanic Cloud (LMC).
Methods. We observed three star-forming regions in the LMC with upGREAT on board SOFIA at the frequency of the [C II] line. The 4 GHz bandwidth covers all three hyperfine lines of [13C II] simultaneously. For the analysis, we combined the [13C II] F = 1−0 and F = 1−1 hyperfine components as they do not overlap with the [12C II] line in velocity.
Results. Three positions in N159 and N160 show an enhancement of [13C II] compared to the abundance-ratio-scaled [12C II] profile. This is likely due to the [12C II] line being optically thick, supported by the fact that the [13C II] line profile is narrower than [12C II], the enhancement varies with velocity, and the peak velocity of [13C II] matches the [O I] 63 μm self-absorption. The [12C II] line profile is broader than expected from a simple optical depth broadening of the [13C II] line, supporting the scenario of several PDR components in one beam having varying [12C II] optical depths. The derived [12C II] optical depth at three positions (beam size of 14″, corresponding to 3.4 pc) is 1−3, which is similar to values observed in several Galactic sources shown in previous studies. If this also applies to distant galaxies, the [C II] intensity will be underestimated by a factor of approximately 2.
Key words: ISM: lines and bands / photon-dominated region (PDR) / Magellanic Clouds
© ESO 2019
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