All Figures

$\begin{figure} \par\includegraphics[width=7.4cm,clip]{3845fig1.eps} \end{figure}$ Figure 1: The solid and dashed line represent the points in $n-\chi$ -parameter space where $\Lambda _{\rm OI}=\Lambda _{\rm CII}$ for metallicities of Z=1 and Z=0.2 respectively.
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In the text

$\begin{figure} \par\includegraphics[width=7.4cm,clip]{3845fig2.eps} \end{figure}$ Figure 2: The solid and dashed line represent the points in $n-\chi$ -parameter space where $\Gamma _{\rm H_2^*,net}=\Gamma _{\rm PE}$ for metallicities of Z=1 and Z=0.2 respectively.
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In the text

$\begin{figure} \par\includegraphics[width=8.4cm,clip]{3845fig3}\par\includegraph... ...4cm,clip]{3845fig4}\par\includegraphics[width=8.4cm,clip]{3845fig5} \end{figure}$ Figure 3: Comparison of the KOSMA- $\tau$ results (open symbols) and the semi-analytic values (filled symbols) for the surface temperature against the metallicity. The top panel a) is for an UV field of $\chi =10^6$ , the bottom plot b) is for $\chi =10^3$ , and the bottom panel c) is for an UV field strength of $\chi =1$ . The different symbols indicate different surface densities.
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm,clip]{3845fig6.eps} \end{figure}$ Figure 4: The width of the C⁺ layer is plotted against the metallicity. The open circles represent spherical clump of mass $M=10^3~M_\odot$ , density n₀=10⁴ cm^-3, FUV field $\chi =100$ , and the power-law index of the density profile, $\gamma =1.5$ , whereas the open squares represent a spherical clump of mass of $10^{6}~M_\odot$ with $\gamma =0$ . The filled circles and squares represent our analytical estimates as explained in Sect. 3.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{3845fig7.eps} \end{figure}$ Figure 5: The surface brightnesses of the [CII] 158 $\mu$ m (dashed-dotted) emission lines from the KOSMA- $\tau$ results (open symbols) and the approximation from Eq. (19) (filled symbols) plotted against the metallicity for different densities. The cloud mass is $M=10~M_\odot$ , the UV field strength is $\chi =100$ , the assumed central temperature is $T_{\rm c}=35$ K, and $\lambda =4$ .
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{3845fig8.eps} \end{figure}$ Figure 6: The surface brightnesses of the [CII] 158 $\mu$ m (dashed-dotted) and ¹²CO(1-0) 2.6 mm (solid) emission lines plotted against the metallicity for two different densities. The cloud mass is $M=10~M_\odot$ and the UV field strength is $\chi =100$ .
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{3845fig9.eps} \end{figure}$ Figure 7: The intensity ratio $I_{{\rm [CII]}158~\mu {\rm m}}$ / $I_{{\rm CO(1-0)}}$ is plotted against the metallicity (Z=1 is equivalent to $12+\log~($ O/H)=8.48). The lines denote the KOSMA- $\tau$ results for two different clump masses M=1 and $M=10~M_\odot$ . The density at the surface of the clumps and the UV field strength in units of the standard Draine field are given in the plot. The observed ratios of nearby galaxies are plotted as squares.
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In the text

$\begin{figure} \par\mbox{\includegraphics[width=8.5cm]{3845fi10.eps}\hspace*{1.5cm} \includegraphics[width=8.5cm]{3845fi11.eps} }\end{figure}$ Figure B.1: The relative contribution of the various electron donors to the total electron density $n_{\rm e}$ at the cloud surface as computed in the KOSMA- $\tau$ model. The percentages are given for different values of surface density n (columns) at FUV fields $\chi =1$ ( left) and $\chi =10^6$ ( right) and a fixed metallicity of Z=0.2.

In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{3845fi12.eps} \end{figure}$ Figure B.2: A comparison of numerically obtained electron densities (symbols) with the analytical expression (lines) in Eq. (B.4), at $A_{\rm V}=0$ , $\chi =10^6$ , Z=1 for different surface densities.

In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{3845fi13.eps}\par\vspace{2mm} \includegraphics[width=8.5cm,clip]{3845fi14.eps} \end{figure}$ Figure C.1: The net H₂ heating rate is plotted for different values of surface density n at a $\chi =1$ FUV field ( top) and for different UV field strengths for a fixed density of n=10³ cm^-3 ( bottom) over the temperature. The symbols are the numerical results from the 15-level system in the KOSMA- $\tau$ model, the curves show the results using our effective two-level approximation. For $\chi =1$ we also plot a low Z case (solid, Z=1, and dashed, Z=0.2). The deviations at the highest temperatures and radiation fields are due to cooling transitions from higher vibrational levels in this regime which are ignored in our approximation.

In the text

$\begin{figure} \par\includegraphics[width=7.4cm,clip]{3845fig1.eps} \end{figure}$	Figure 1: The solid and dashed line represent the points in $n-\chi$ -parameter space where $\Lambda _{\rm OI}=\Lambda _{\rm CII}$ for metallicities of Z=1 and Z=0.2 respectively.
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$\begin{figure} \par\includegraphics[width=7.4cm,clip]{3845fig2.eps} \end{figure}$	Figure 2: The solid and dashed line represent the points in $n-\chi$ -parameter space where $\Gamma _{\rm H_2^*,net}=\Gamma _{\rm PE}$ for metallicities of Z=1 and Z=0.2 respectively.
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$\begin{figure} \par\includegraphics[width=8.4cm,clip]{3845fig3}\par\includegraph... ...4cm,clip]{3845fig4}\par\includegraphics[width=8.4cm,clip]{3845fig5} \end{figure}$	Figure 3: Comparison of the KOSMA- $\tau$ results (open symbols) and the semi-analytic values (filled symbols) for the surface temperature against the metallicity. The top panel a) is for an UV field of $\chi =10^6$ , the bottom plot b) is for $\chi =10^3$ , and the bottom panel c) is for an UV field strength of $\chi =1$ . The different symbols indicate different surface densities.
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$\begin{figure} \par\includegraphics[width=8cm,clip]{3845fig7.eps} \end{figure}$	Figure 5: The surface brightnesses of the [CII] 158 $\mu$ m (dashed-dotted) emission lines from the KOSMA- $\tau$ results (open symbols) and the approximation from Eq. (19) (filled symbols) plotted against the metallicity for different densities. The cloud mass is $M=10~M_\odot$ , the UV field strength is $\chi =100$ , the assumed central temperature is $T_{\rm c}=35$ K, and $\lambda =4$ .
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$\begin{figure} \par\includegraphics[width=7.8cm,clip]{3845fig8.eps} \end{figure}$	Figure 6: The surface brightnesses of the [CII] 158 $\mu$ m (dashed-dotted) and ¹²CO(1-0) 2.6 mm (solid) emission lines plotted against the metallicity for two different densities. The cloud mass is $M=10~M_\odot$ and the UV field strength is $\chi =100$ .
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