  Although the 2P3/2-2P1/2 transition of [CII] at 158um is known to be an
excellent tracer of active star formation, we still do not have a complete
understanding of where within star formation regions the emission originates.
Here, we use SOFIA upGREAT observations of [CII] emission toward the HII region
complex Sh2-235 (S235) to better understand in detail the origin of [CII]
emission. We complement these data with a fully-sampled Green Bank Telescope
radio recombination line map tracing the ionized hydrogen gas. About half of
the total [CII] emission associated with S235 is spatially coincident with
ionized hydrogen gas, although spectroscopic analysis shows little evidence
that this emission is coming from the ionized hydrogen volume.
Velocity-integrated [CII] intensity is strongly correlated with WISE 12um
intensity across the entire complex, indicating that both trace ultra-violet
radiation fields. The 22um and radio continuum intensities are only correlated
with [CII] intensity in the ionized hydrogen portion of the S235 region and the
correlations between the [CII] and molecular gas tracers are poor across the
region. We find similar results for emission averaged over a sample of external
galaxies, although the strength of the correlations is weaker. Therefore,
although many tracers are correlated with the strength of [CII] emission, only
WISE 12um emission is correlated on small-scales of the individual HII region
S235 and also has a decent correlation at the scale of entire galaxies. Future
studies of a larger sample of Galactic HII regions would help to determine
whether these results are truly representative.
