\begin{table}%t4
%\centering
\par
\caption{\label{tab.masses}Molecular gas masses, $\ratioo$ conversion factor and characteristic time to transform molecular gas into stars derived from IR emission.}
\begin{tabular}{lrrrr}
\hline \hline \noalign{\smallskip}
& Total ${M_{{\rm H}_{2}}}$ & Map ${M_{{\rm H}_{2}}}$ & $\ratioo$ & $\tau$\\
& ${M_{\sun}}$& ${M_{\sun}}$ & ${\rm \frac{cm^{-2}}{{K\kms}}}$ & yr \\[1ex]
\hline \noalign{\smallskip}
${\rm 8~\mu m}$ & $9.2\times10^6$ &$5.7\times10^6$ & $5.3\times10^{21}$ & $2.2\times10^8$\\
$160~{\rm \mu m}$& ${4.6\times10^{6}}$ & $3.4\times10^{6}$&$2.3\times10^{21}$ & $1.3\times10^8$ \\
\hline
\end{tabular}
\tablefoot{The second column refers to the area mapped in CO. The last column is the inverse of the SFE.}
\end{table}