collisions in the H [ii]{} regions and to the photoelectric effect and cosmic rays in the neutral phase, the cooling is normally dominated by radiative de-excitation of fine-structure lines, readily observed in the MIR and FIR/submm. The behavior of these tracers and their relationship to the star formation properties, have been extensively studied to access physical parameters in terms of the gas temperature, density, and the radiation field [@malhotra-2001; @hunter-2001; @brauher-2008 e.g.]. These sudies make use of photoionisation and PDR models at the scale of individual clouds [@kaufman-1999; @wolfire-1990; @ferland-1998; @abel-2005; @roellig-2006; @tielens-hollenbach-1985].

The \[C [ii]{}\] 157 $\mu$m line is an important FIR diagnostic often put forward as a star formation tracer [@stacey-2010; @boselli-2002; @delooze-2011]. It has been observed in many different object types, including dense star-forming regions [@stacey-1991], diffuse ionised and atomic regions [@madden-1993], and high-redshift galaxies [@maiolino-2009; @stacey-2010]. Since the \[C [ii]{}\] line is well-correlated with the $^{12}$CO(1-0) line and the FIR luminosity [e.g. @stacey-1991; @pierini-2003], it is generally considered that the \[C [ii]{}\] line traces massive star formation within the PDR paradigm. \[C [ii]{}\] is normally the brightest FIR cooling line, being much brighter than CO, and carrying about 0.1 to $\sim$0.5% of the FIR luminosity in 