\begin{table}%t1
\caption{\label{tab:MW}Properties of gas components of the Milky Way. }
%\begin{tabular}{rcccc}
%\hline
%Component  & $M$ $(10^9~$$M_\odot)^a$& L$_{\rm d}$ $($pc$)^b$  & $\sigma$ $($km$~$s$^{-1})^c$ & $E_{\rm kin}$ ($10^{55}~$erg$~$s$^{-1})^d$\\[0.3cm]
%\hline
% molecular gas & 2 & 150 & 5 & 8.6\\
% atomic gas$^e$ & 6 & 1000$^f$ & 12 & 0.5\\
% \hline
%\end{tabular}
%\centerline
{
\begin{tabular}{lcc}
\hline\hline
Component  &molecular gas & atomic gas\\
\hline\\[-0.3cm]
 $M$ $(10^9~$$M_\odot)$\tablefootmark{a}& 2 &6\\
 $L_{\rm d}$ (pc)\tablefootmark{b}  & 150 & 1000\\
 $\sigma$ (km~s$^{-1}$)\tablefootmark{c} & 5 & 12\\
 $E_{\rm kin}$ ($10^{55}$~erg~s$^{-1}$)\tablefootmark{d} & 0.5 & 8.6\\
 \hline
\end{tabular}}
\tablefoot{\tablefoottext{a}{Total mass of the component. Values from \citet{Ferriere:2001p2879} and \citet{Kalberla:2003p2981}.}
\tablefoottext{b}{We take twice the observed disk scale height as the true thickness to be considered.}
\tablefoottext{c}{The parameter $\sigma$ is the 3-dimensional velocity dispersion. We take the 1-dimensional velocity dispersion of the molecular gas to be $2.9~$km$~$s$^{-1}$ and of the HI gas to be $6.9~$km$~$s$^{-1}$.}
\tablefoottext{d}{Total kinetic energy of the component, $E_{\rm kin} = 1/2 ~ M \sigma^2$.}}
\end{table}