\begin{table}%t2
%\centering
\par
\caption {\label{tab2}M~31 data used in this study. }
\begin{tabular}{ l l l l} 
\hline\hline
\noalign{\smallskip}
Wavelength & Resolution & Telescope  &   Ref. \\
\hline
160~$\mu$m             &  $40\arcsec$ & Spitzer& \cite{Gordon_06}\\
70~$\mu$m               &  $18\arcsec$ & Spitzer&\cite{Gordon_06}\\
24~$\mu$m             &  $6\arcsec$ & Spitzer & \cite{Gordon_06} \\
2.6~mm~$^{12}$CO(1--0)           &  $23\arcsec$ &IRAM 30-m & \cite{Nieten} \\
21~cm~HI               &  24$\arcsec ~ \times ~30\arcsec$ & WSRT &\cite{Brinks}\\
6570 \AA{}~H$\alpha$   &  $2\arcsec$ (pixel size)  & KPNO& \cite{Devereux_etal_94b}\\
\hline
\end{tabular}
\end{table}