\begin{table}%t6
%\centering
\par
\caption {\label{table:dustgas2}Power-law relations and correlation coefficients $r_{\rm c}$  between  the emission from dust and ionized gas. }
\begin{tabular}{ l l l l l l l l}
\hline\hline
\noalign{\smallskip}
  $X$    &    $Y$ &     $R$   &  ~~~~~~     $a_{\rm c}$  & ~~~~~~$b$ &    $n$  &  ~~~~~~
  $r_{\rm c}$  & $t$\\
($10^{-7}$ erg~s$^{-1}$~cm$^{-2}$~sr$^{-1}$) & (MJy/sr) & ($\arcmin$)& & &  & &\\
\hline
 $I_{{\rm H}\alpha}$ &$I_{24~\mu{\rm m}}$ &   0--30   & --1.76~$\pm$~0.05 &  0.94~$\pm$~0.03 &   417 &  0.79~$\pm$~0.03 &   27\\  
            &  & 30--50 &  --1.75~$\pm$~0.05  & 1.00~$\pm$~0.03  &  677  & 0.75~$\pm$~0.03 &   30\\     
             &  &  0--50  &  --1.75~$\pm$~0.05  &0.98~$\pm$~0.02  & 1094 &  0.76~$\pm$~0.02  &  38\\
& & & & & & &\\
$I_{{\rm H}\alpha}$ & $I_{70\mu{\rm m}}$ &   0-30   & --1.04~$\pm$~0.03 & 1.10~$\pm$~0.03  &  412  & 0.83~$\pm$~0.03 &   30\\
           &   &  30--50    &--0.96~$\pm$~0.03   &1.09~$\pm$~0.03  &  677  & 0.78~$\pm$~0.02  &  32  \\ 
            &    &  0--50    &--0.98~$\pm$~0.02  &1.09~$\pm$~0.02   & 1089  & 0.79~$\pm$~0.02   & 43 \\
& & & & & & &\\
 $I_{{\rm H}\alpha}$& $I_{160\mu{\rm m}}$ & 0-30 & 0.26~$\pm$~0.05 & 0.76~$\pm$~0.03 &  417 & 0.54~$\pm$~0.04 & 13\\
            &  &  30--50  &0.47~$\pm$~0.04  &0.72~$\pm$~0.02 &  678  & 0.73~$\pm$~0.03  &  28  \\ 
\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}