First detection of [13C？II] in the Large Magellanic Cloud

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}