only the neutral phase. The \[O [i]{}\] 63 $\mu$m/\[C [ii]{}\] ratio is 0.9, similar to that found in other dwarf galaxies and dustier galaxies [@hunter-2001; @brauher-2008]. Table \[table:lines\] lists the ionisation energies of the observed lines, as well as the excitation temperatures and critical densities (n$_{crit}$) of the transitions with collisions with H and/or e$^-$.

Comparing line luminosities to the TIR luminosity, we find L$\rm{_{[C~II]}}$/L$\rm{_{TIR}}$ = 0.1%, L$\rm{_{[O~III]}}$/L$\rm{_{TIR}}$ = 0.3%, and L$\rm{_{[O~I]}}$/L$\rm{_{TIR}}$ = 0.1%. Altogether, the FIR lines represent 0.6% of the TIR luminosity; and when adding the MIR lines, they represent 1.2% of L$\rm{_{TIR}}$. Together these lines are responsible for most of the gas cooling of the ISM. Such line-to-TIR ratios are typical of star-forming galaxies [@malhotra-2001; @brauher-2008][^4]. Similar L$\rm{_{[C~II]}}$/L$\rm{_{TIR}}$ ratios are found in several high-redshift galaxies [@maiolino-2009; @stacey-2010]. [@croxall-2012] find $\rm{L_{[C~II]}/L_{TIR}\sim0.5\%}$ and $\rm{L_{[O~I]}/L_{TIR}\sim0.1\%}$ in spatially resolved regions of the nearby spiral galaxy NGC 4559. There is observational evidence that L$\rm{_{[C~II]}}$/L$\rm{_{TIR}}$ tends to decrease in galaxies with warmer FIR-color, f$_{\nu}$(60 $\mu$m)/f$_{\nu}$(100 $\mu$m). Among other effects, this may be attributed to a less efficient photoelectric heating due to charged grains [@malhotra-2001; @croxall-2012], or to a UV-photon screening from large amounts of dust as in ultra-luminous IR galaxies (ULIRGs) [@abel-2009; @gracia-2011]. 