\begin{table}%t2
\caption{\label{table:2} Average properties of IRDCs and fragments (extracted with $\tau_{\rm{step}}=0.35$). } 
\small \begin{tabular}{ccccccccccc} 
  \hline   \hline
Structures &   Number of  & \multicolumn{2}{c}{$R_{\rm{eq}}$} & \multicolumn{2}{c}{Aspect ratio} &\multicolumn{2}{c}{$\tau_{\rm{av}}$}  & \multicolumn{2}{c}{$\tau_{\rm{peak}}$}  & Star association \\
 & objects & Average & Range &  Average & Range &  Average & Range &  Average & Range & \\
    & & (arcsec) &(arcsec) & & & &   &  & &$\%$ \\
%\endhead
\hline
   IRDCs  &   11303 &  31 & 4--374 & 2.2 & 1.0--11.6 & 0.15 & 0.01--2.35
   & 1.15 & 0.70 -- 8.36 & 20-68\\
    Fragments  &   19838 &  19 & 1--205  & 2.0 &
    1.0--11.6 & 0.75 & 0.01--7.88 & 1.63 & 0.70 -- 8.36 & 6\\ 
  \hline   
\end{tabular}
\end{table}