Large column densities and [12CII] 158 μm self-absorption in Orion B

We present a preliminary analysis of the self-absorbed [CII]-spectra observed with SOFIA/GREAT towards NGC 2024. Together with the detected [¹³CII] hyperfine satellites, the observed spectra require surprisingly high column densities of C⁺, both in the warm core and the foreground absorption component. Such high column densities are a challenge to explain with present state-of-the-art PDR models of the UV/molecular cloud interaction.