\begin{table}%T2
  \caption{\label{expdisc_m51}Properties of the exponential disk of the total gas
derived in this paper compared to the properties of the exponential dust disk 
determined by \citet[][]{Meijerink2005}.}
\small%\centering
\par
\begin{tabular}{ll}   
\hline \hline   
Total gas exponential disk: \\
$\Sigma_{\rm gas}$ scale length $h_{\rm gas}$ & 7.6 $\pm 0.1$~kpc \\
Amplitude: $\Sigma^{\rm peak}_{\rm gas}$  & 17.8 $\pm 0.2$~\msun~pc$^{-2}$ \\
disk/total mass-fraction gas  & 61\% \\ 
\noalign{\smallskip} \hline \noalign{\smallskip}   
Dust exponential disk: \\
dust scale length $h_{\rm d}$ & 6.3~kpc \\
Amplitude: $\Sigma^{\rm peak}_{\rm dust}$ & 0.77 $\pm 0.2$~\msun~pc$^{-2}$ \\ 
disk/total mass-fraction dust & 55\% \\  \hline  
\end{tabular}   
\end{table}