First detection of [13CII] in the Large Magellanic Cloud
  [13CII] observations in several Galactic sources show that the fine-structure
[12CII] emission is often optically thick (the optical depths around 1 to a
few). The aim of our study is to test whether this also affects the [12CII]
emission from nearby galaxies like the Large Magellanic Cloud (LMC). We
observed three star-forming regions in the LMC with upGREAT on board SOFIA at
the frequency of the [CII] line. The 4GHz band width covers all three hyperfine
lines of [13CII] simultaneously. For the analysis, we combined the [13CII]
F=1-0 and F=1-1 hyperfine components, as they do not overlap with the [12CII]
line in velocity. Three positions in N159 and N160 show an enhancement of
[13CII] compared to the abundance-ratio-scaled [12CII] profile. This is likely
due to the [12CII] line being optically thick, supported by the fact that the
[13CII] line profile is narrower than [12CII], the enhancement varies with
velocity, and the peak velocity of [13CII] matches the [OI] 63um
self-absorption. The [12CII] line profile is broader than expected from a
simple optical depth broadening of the [13CII] line, supporting the scenario of
several PDR components in one beam having varying [12CII] optical depths. The
derived [12CII] optical depth at three positions (beam size of 14arcsec,
corresponding to 3.4pc) 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 [CII] intensity will be underestimated by a factor of
approximately 2.
