\begin{table}%T6
\caption{\label{table:parameters}Linear radii, masses, and H$_2$ column and volume-averaged number
densities of the submm clumps within the IRDC G304.74.}
\vspace*{-2.5mm}
\small
%\centering

\begin{tabular}{c c c c c c c c}
\hline\hline \noalign{\smallskip}
       & $R_{\rm eff}$ & $M_{\rm cont}$ & $N_{870}({\rm H_2})$ & $N_{8}({\rm H_2})$ &  & $ \langle n({\rm H_2}) \rangle $\\ 
Source & [pc] & [$M_{\sun}$] & [$10^{22}$~cm$^{-2}$] & [$10^{22}$~cm$^{-2}$] & $N_{870}/N_{8}$ & [$10^4$~cm$^{-3}$]\\  
\hline
SMM~1\tablefootmark{a} & 0.42 & 107 & $2.06\pm0.13$ & $0.74\pm0.30$ & $2.8\pm1.1$ & 0.7\\
SMM~2\tablefootmark{b} & 0.33 & 53 & $1.35\pm0.14$ & $0.54\pm0.27$ & $2.5\pm1.3$ & 0.7\\
SMM~3\tablefootmark{c} & 0.49 & 182 & $2.24\pm0.13$ & 0.14\tablefootmark{d} & $16\pm0.9$ & 0.7\\
SMM~4\tablefootmark{e} & 0.44 & 219 & $2.96\pm0.13$ & $0.36\pm0.24$ & $8.2\pm5.5$ & 1.2\\
IRAS~13037-6112 & 0.30 & 48 & $1.17\pm0.07$ & -- & -- & 0.8\\
SMM~5 & 0.30 & 37 & $0.85\pm0.13$ & $1.79\pm0.57$ & $0.5\pm0.2$ & 0.6\\
SMM~6 & 0.35 & 96 & $2.06\pm0.13$ & -- & -- & 1.0\\
SMM~7 & 0.35 & 48 & $1.17\pm0.14$ & $1.74\pm0.56$ & $0.7\pm0.2$ & 0.5\\
IRAS~13039-6108 & 0.47 & 78 & $1.18\pm0.08$ & -- & -- & 0.3\\
SMM~8 & 0.34 & 59 & $1.39\pm0.13$ & $2.23\pm0.76$ & $0.6\pm0.2$ & 0.7\\
SMM~9 & 0.37 & 85 & $1.70\pm0.13$ & $3.13\pm1.40$ & $0.5\pm0.2$ & 0.8\\
IRAS~13042-6105 & 0.31 & 43 & $0.94\pm0.13$ & -- & -- & 0.7\\
\hline 
\end{tabular}
\vspace*{-2mm}
\tablefoot{\tablefoottext{a}{By assuming $T_{\rm d}=30$ K (see Sect.~4.3 and Table~\ref{table:extinction}), $M_{\rm cont}=39~M_{\odot}$, $N_{870}({\rm H_2})=0.75\pm0.05\times10^{22}$~cm$^{-2}$, $N_{870}/N_{8}=1.0\pm0.1$, and $\langle n({\rm H_2}) \rangle=0.2\times10^4$~cm$^{-3}$.}\\
\tablefoottext{b}{By assuming $T_{\rm d}=30$ K, 
$M_{\rm cont}=20~M_{\odot}$, $N_{870}({\rm H_2})=0.49\pm0.05\times10^{22}$ 
cm$^{-2}$, $N_{870}/N_{8}=0.9\pm0.1$, and $\langle n({\rm H_2}) \rangle=0.3\times10^4$~cm$^{-3}$.}\\
\tablefoottext{c}{By assuming $T_{\rm d}=30$ K, 
$M_{\rm cont}=66~M_{\odot}$, $N_{870}({\rm H_2})=0.82\pm0.05\times10^{22}$ 
cm$^{-2}$, $N_{870}/N_{8}=5.9\pm0.4$, and $\langle n({\rm H_2}) \rangle=0.3\times10^4$~cm$^{-3}$.}\\
\tablefoottext{d}{No error given because it is greater than the actual value.}\\
\tablefoottext{e}{By assuming $T_{\rm d}=30$ K, 
$M_{\rm cont}=80~M_{\odot}$, $N_{870}({\rm H_2})=1.08\pm0.05\times10^{22}$ 
cm$^{-2}$, $N_{870}/N_{8}=3.0\pm2.0$, and $\langle n({\rm H_2}) \rangle=0.4\times10^4$~cm$^{-3}$.}}
\vspace*{-1mm}
\end{table}