\begin{table}%t6
\caption{\label{Table: max signal}Estimated largest possible  brightness temperature~$T_{\rm b}$ for   {\it optically thick   resonant} lines,  and $\upsilon_p(z)$~=~$600/\sqrt{1+z}$~\kms.}
%\centering
\par
\begin{tabular}{cccc}
\hline \hline \noalign{\smallskip}
Obs. Freq.   &  \multicolumn{3}{c}{Maximum   $\mid   T_{\rm b} \mid $  [mK]}\\ 
 $[$GHz$]$ & $z$ = 10 	 	& $z$ = 30	& $z$ = 100\\
\hline
   1	& 1.6	& 	0.98		&	0.54  	\\
50	&1.5	& 	0.92		&	0.51\\
100	&1.3	& 	0.76		&	0.42	\\
200	&0.64	& 	0.38		&	0.21	\\
300	&0.24	& 	0.14		&	0.078	\\
400	&0.071& 	0.042	&	0.024	\\
500	&0.019& 	0.011	&	0.006	\\
600	&0.005& 	0.003	&	0.002	\\
\hline
\end{tabular}
\tablefoot {This velocity is typical for clusters while for a smaller mass it could be higher. 
Note, that these values are the same for {\it all} species and transitions.} 
\end{table}