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The [CII] fine-structure transition at 158 micron is frequently the brightestfar-infrared line in galaxies. Due to its low ionization potential, C+ cantrace the ionized, atomic, and molecular phases of the ISM. We present velocityresolved [CII] and [NII] pointed observations from SOFIA/GREAT on ~500 pcscales in the nearby galaxies M101 and NGC 6946 and investigate the multi-phaseorigin of [CII] emission over a range of environments. We show that ionized gasmakes a negligible contribution to the [CII] emission in these positions using[NII] observations. We spectrally decompose the [CII] emission into componentsassociated with the molecular and atomic phases using existing CO(2-1) and HIdata and show that a peak signal-to-noise ratio of 10-15 is necessary for areliable decomposition. In general, we find that in our pointings greater thanor equal to 50% of the [CII] emission arises from the atomic phase, with nostrong dependence on star formation rate, metallicity, or galactocentricradius. We do find a difference between pointings in these two galaxies, wherelocations in NGC 6946 tend to have larger fractions of [CII] emissionassociated with the molecular phase than in M101. We also find a weak butconsistent trend for fainter [CII] emission to exhibit a larger contributionfrom the atomic medium. We compute the thermal pressure of the cold neutralmedium through the [CII] cooling function and find log(P_th/k)=3.8-4.6 [Kcm^-3], a value slightly higher than similar determinations, likely because ourobservations are biased towards star-forming regions.

Characterizing the Multi-Phase Origin of [CII] Emission in M101 and NGC 6946 with Velocity Resolved Spectroscopy