\begin{table}%t3
%%\centering

\par
\caption{\label{tab:simulazioni2}Separation threshold for aligned groups.}
\begin{tabular}{cc|rr}
\hline  \hline
 \multicolumn{2}{c}{Distance} & \multicolumn{2}{|c}{Separation threshold} \\
 Redshift  & Projected  & $z \sim 1$   & $z \sim 2$ \\
\hline
  &$\Delta r=1.0$ Mpc &     >$8\sigma$      &  >$8\sigma$      \\
 1$\sigma_z$ &$\Delta r=1.5$ Mpc & 6$\sigma$    & 5$\sigma$\\
  &$\Delta r=2.0$ Mpc & 4$\sigma$    & 5$\sigma$\\
\hline
 & $\Delta r=1.0$ Mpc &    >$8\sigma$    &   >$8\sigma$      \\
 2$\sigma_z$& $\Delta r=1.5$ Mpc & 4$\sigma$    & 5$\sigma$\\
  &$\Delta r=2.0$ Mpc & 4$\sigma$    & 5$\sigma$\\
\hline
& $\Delta r=1.0$ Mpc & 5$\sigma$   & 5$\sigma$\\
 3$\sigma_z$& $\Delta r=1.5$ Mpc & 4$\sigma$    & 5$\sigma$\\
 & $\Delta r=2.0$ Mpc & 4$\sigma$    & 5$\sigma$\\
\hline
\end{tabular}
\end{table}