\begin{table}%t3
%\centering
\par
\caption{$R_{21}$ line ratio for spiral arms of M~81 by \citet{brouillet2}.}
\begin{tabular}{lrccc}
\hline\hline
Field       & Offsets &$\int T_{\rm mb}$(1--0)d$v$ &$\int T_{\rm mb}$(2--1)d$v$ & $R_{21}$ \\		& ($^{\prime\prime}$,$^{\prime\prime}$)&[K~km~s$^{-1}$]&[K~km~s$^{-1}$]&\\
\hline
\textbf{N1}	&	$(0,0)$	    &	1.14        &        2.11        &        1.85              \\
\textbf{N5}	&	$(0,0)$	    &	1.52        &        0.70        &        0.46               \\
   	        &	$(10,0)$	    &	1.27        &        1.05        &        0.83               \\
            	&	$(-10,0)$	    &	1.39        &        0.70        &        0.50               \\
	        &	$(20,0)$	    &	0.89        &        0.53        &        0.59               \\
	        &	$(-20,0)$	    &	1.52        &        1.05        &        0.69               \\
	        &	$(20,-10)$     &	2.03        &        1.05        &        0.52               \\
\textbf{N7}	&	$(0,0)$	    &	2.53        &        1.23        &        0.49               \\
	        &	$(20,0)$	    &   1.52        &        1.93        &        1.27               \\
	        &	$(-20,0)$	    &	2.28        &        1.05        &        0.46               \\
	        &	$(0,20)$	    &	0.51        &        1.40        &        2.77               \\
	        &	$(0,-20)$	    &	1.39        &        4.04        &        2.90               \\
\textbf{S2}	&	$(-10,0)$	    &	0.76        &        1.05        &        1.39               \\
 	        &	$(0,-10)$	    &	2.03        &        2.28        &        1.13               \\
	        &	$(20,0)$	    &	2.03        &        1.40        &        0.69               \\
     		&	$(-20,0)$	    &   1.65        &        1.40        &        0.85   \\
\hline
\end{tabular}
\label{table3}
\end{table}