\begin{table}%t5
%\centering
\par
\caption {\label{table:dustgas1}Power-law relations and correlation coefficients $r_{\rm c}$ between dust extinction and gas components. }
\begin{tabular}{ l l l l l l l l} 
\hline\hline
\noalign{\smallskip}
  $X$    &    $Y$ &     $R$    &  ~~~~~~     $a_{\rm c}$  &~~~~~~ $b$ &    $n$  & ~~~~~~ $r_{\rm c}$  & $t$\\
 ($10^{18}$ at~cm$^{-2}$)& (mag) & ($\arcmin$) &&&&& \\
\hline
$N$(2H$_2$) & $A_{\rm H\alpha}$ & 0--30 &   --1.88~$\pm$~0.06 &  0.53~$\pm$~0.03 &   207&   0.60~$\pm$~0.06 &   11\\
   &      & 30--50 &   --1.83~$\pm$~0.04 &  0.52~$\pm$~0.02 &   610  & 0.64~$\pm$~0.03 &   20 \\
        &     &   0--50 &   --1.85~$\pm$~0.03 &  0.52~$\pm$~0.01 &   817 &  0.63~$\pm$~0.03 &   23\\
& & & & & & &\\
\par
$N$(HI) &  A$_{\rm H\alpha}$ &  0--30 &  --3.29~$\pm$~0.11 &  0.94~$\pm$~0.04 &   354 &  0.69$\pm$0.04&    18\\
      &        & 30--50 &  --3.26~$\pm$~0.07 &  0.84~$\pm$~0.02 &   768 &  0.72~$\pm$~0.03 &   29\\  
&&&&&&&\\   
$N$(gas) & A$_{\rm H\alpha}$ & 0--30 &   --2.97~$\pm$~0.08 &  0.79~$\pm$~0.03 &   350 &  0.80~$\pm$~0.03 &   25\\
      &     & 30--50 &   --3.05~$\pm$~0.06 &  0.76~$\pm$~0.02  &  766 &  0.77~$\pm$~0.02  &  33\\  
\hline
\end{tabular}
\tablefoot {Ordinary least-squares fits of bisector log~($Y$)~=~$a_{\rm c}+b$~log~($X$) through $n$ pairs of (log~$X$, log~$Y$), where $n$ is the number of independent points (Isobe 
et~al. 1990); $t$ is the student-t test.}
\end{table}