\begin{table}%t1
\caption{Metallicity dependence of the individual heating processes.}\label{tab1}
\small%\centering
\par
\begin{tabular}{ccc}
\hline\hline 
 & Low UV~field & High UV~field\\
 & {\small $\chi < 100$} & {\small $\chi \gg 100 $}\\  \hline \noalign{\smallskip}
high &$\Gamma_{\rm PE}\sim Z$ &$\Gamma_{\rm PE}\sim Z^{~2}$\\
density &$\Gamma_{\rm H_2^*}\sim\frac{Z}{1+2Z}$ &$\Gamma_{\rm H_2^*}\sim Z$ \\
{\small$(n\ga 10^6)$} &$\Gamma_{\rm H_2-form}\sim{Z}$ &$\Gamma_{\rm H_2-form}\sim Z$ \\
& $\Lambda_{\rm rec}\sim Z^{1.5}$ & $\Lambda_{\rm rec}\sim Z^{1.5}$ \\
& $\Lambda_{\rm tot}\sim Z$ & $\Lambda_{\rm tot}\sim Z$ \\
 \hline\noalign{\smallskip} 
low &$\Gamma_{\rm PE}\sim Z$ & $\Gamma_{\rm PE}\sim Z...Z^{1.5}$\\
density &$\Gamma_{\rm H_2^*}\sim Z$& $\Gamma_{\rm H_2^*}\sim Z$\\
{\small$(n\la 10^3)$ }&$\Gamma_{\rm H_2-form}\sim{Z}$ &$\Gamma_{\rm H_2-form}\sim Z$ \\
&$\Lambda_{\rm rec}\sim Z$ &$\Lambda_{\rm rec}\sim Z...Z^{1.5}$ \\
& $\Lambda_{\rm tot}\sim Z$ & $\Lambda_{\rm tot}\sim Z$ \\
 \hline 
\end{tabular}
\end{table}