Table 8: FIR line ratios after correcting the observed [C II] intensities for emission from the ionized medium. We study two cases: the emission of [C II] from the ionized medium originates entirely a) from the diffuse medium, and b), that the emission arises entirely from dense H II regions. Also shown is the intensity ratio $\epsilon$ of the two major cooling lines of PDRs ([O I](63)+[C II] $_{\rm PDR}$ ) vs. the observed TIR continuum.
$\Delta\alpha/\Delta\delta$ [C II] $_{\rm obs}$ [C II] $_{\rm PDR}$ [O I](63) $\epsilon$

[N II](122) [C II] $_{\rm obs}$ [C II] $_{\rm PDR}$ [%]

a) [N II] only from the DIM:

M 83:

0, 0 5.8 0.02 57.41 0.12

-80,-72 7.3 0.22 3.18 0.22

89, 38 5.7 0.00 - 0.17

M 51:

0, 0 3.6 0.00 - 0.08

72, 84 7.3 0.22 3.59 0.16

-84,-84 7.4 0.23 3.78 0.21

b) [N II] only from H II-regions:

M 83:

0, 0 5.8 0.81 1.31 0.21

-80,-72 7.3 0.85 0.83 0.36

89, 38 5.7 0.81 0.99 0.35

M 51:

0, 0 3.6 0.69 1.06 0.16

72, 84 7.3 0.85 0.91 0.25

-84,-84 7.4 0.85 1.02 0.33

**Table 8:** FIR line ratios after correcting the observed [C II] intensities for emission from the ionized medium. We study two cases: the emission of [C II] from the ionized medium originates entirely a) from the diffuse medium, and b), that the emission arises entirely from dense H II regions. Also shown is the intensity ratio $\epsilon$ of the two major cooling lines of PDRs ([O I](63)+[C II] $_{\rm PDR}$ ) vs. the observed TIR continuum.
$\Delta\alpha/\Delta\delta$	[C II] $_{\rm obs}$	[C II] $_{\rm PDR}$	[O I](63)	$\epsilon$
	[N II](122)	[C II] $_{\rm obs}$	[C II] $_{\rm PDR}$	[%]
a) [N II] only from the DIM:
M 83:
0, 0	5.8	0.02	57.41	0.12
-80,-72	7.3	0.22	3.18	0.22
89, 38	5.7	0.00	-	0.17
M 51:
0, 0	3.6	0.00	-	0.08
72, 84	7.3	0.22	3.59	0.16
-84,-84	7.4	0.23	3.78	0.21
b) [N II] only from H II-regions:
M 83:
0, 0	5.8	0.81	1.31	0.21
-80,-72	7.3	0.85	0.83	0.36
89, 38	5.7	0.81	0.99	0.35
M 51:
0, 0	3.6	0.69	1.06	0.16
72, 84	7.3	0.85	0.91	0.25
-84,-84	7.4	0.85	1.02	0.33

Source LaTeX | All tables | In the text

	1 Introduction
	2 Data sets
	3 Spectra and line ratios
	4 Physical conditions
	5 Summary
	References
	Online Material