SOFIA CII and NII obs. of M101 and NGC6946

Due to its low ionization potential, C+ can trace the ionized, atomic, and molecular phases of the ISM. We present velocity-resolved [CII] and [NII] pointed observations from SOFIA/GREAT on ~500pc scales in the nearby galaxies M101 and NGC 6946 and investigate the multiphase origin of [CII] emission over a range of environments.

We show that ionized gas makes a negligible contribution to the [CII] emission in these positions using [NII] observations. We spectrally decompose the [CII] emission into components associated with the molecular and atomic phases using existing CO (2-1) and HI data and show that a peak signal-to-noise ratio of 10-15 is necessary for a reliable decomposition. In general, we find that in our pointings >~50% of the [CII] emission arises from the atomic phase, with no strong dependence on star formation rate, metallicity, or galactocentric radius.