\begin{table}%T3
\caption{\label{equivwidths_m51_properties}Equivalent widths $\Delta v_{\rm eq}$ of CO~and \HI~  in M~51 averaged over the
  areas shown in Fig.~\ref{total_gas}.}
  \small%\centering
\par
\begin{tabular}{lrr}   
\hline \hline   
                             & $\Delta v_{\rm eq} (\rm CO)$ & $\Delta v_{\rm
                               eq}(\HI\ )$ \\ 
                             & [km s$^{-1}$] & [km s$^{-1}$] \\ 
\noalign{\smallskip} \hline \noalign{\smallskip}   
inner spiral arms & 25.9 & 21.5 \\               
outer spiral arms & 11.1 & 18.3 \\                   
interarm region & 7.3 & 19.4 \\                   
\hline               
ratio inner/outer spiral & 2.3 & 1.2 \\
inner arm/interarm       & 3.6 & 1.1 \\
outer arm/interarm       & 1.5 & 0.9 \\  
\hline  
\end{tabular}   
\end{table}