\begin{table}%t7
%\centering
\par
\caption {\label{table:sfr}Kennicutt-Schmidt law in M~31 for $30\arcmin<R<50\arcmin$.  }
\begin{tabular}{ l l l l l l l}
\hline\hline
\noalign{\smallskip}
$\Sigma$($M_{\odot}$~pc$^{-2}$)   & ~~~~~~~~  $a_{\rm c}$  &~~~~~~ $b$ &    $n$  & ~~~~~~ $r_{\rm c}$& $t$\\
\hline
$\Sigma_{\rm 2H_{2}}$ &  --0.15~$\pm$~0.01 &  0.96~$\pm$~0.03 &   537 &  0.45~$\pm$~0.04& 12 \\
$\Sigma_{\rm HI}$     &    --1.08~$\pm$~0.03 &  1.40~$\pm$~0.05  &  670  & 0.55~$\pm$~0.03& 17 \\
$\Sigma_{\rm GAS}$  &  --1.12~$\pm$~0.03 &  1.30~$\pm$~0.05 &  668 & 0.59~$\pm$~0.03& 19 \\
\hline
\end{tabular}
\tablefoot {Ordinary-least squares fits of the bisector log~($\Sigma_{\rm SFR}$)~=~$a_{\rm c}+b$~log~($\Sigma$), where $\Sigma_{\rm SFR}$ is the face-on surface density of the star formation rate in $M_{\odot}$~Gyr$^{-1}$~pc$^{-2}$ and~$\Sigma$ the face-on value of the gas surface density in $M_{\odot}$~pc$^{-2}$; $n$ is the number of independent points; $r_{\rm c}$ is the correlation coefficient and~$t$ the student-t test.}
\end{table}