\begin{table}%t2
\caption{\label{samples}Related \textit{Spitzer}-selected $z\sim2$ ULIRGs samples.}
%\centerline
  {\begin{tabular}{lcccccc}
\hline\hline
Sample         & $N$ & $F_{\rm{24~\mu m}}$ & $\langle  F_{\rm{24~\mu m}}\rangle$ & IR color selection & $r$    & density    \\
\hline
               &   & $\mu$Jy  & $\mu$Jy &      & Vega & deg$^{-2}$ \\
This work                      &     33   & \textgreater400 & 566  & $F_{\rm{3.6~\mu m}}$\textless $F_{\rm{4.5~\mu m}}$\textless $F_{\rm{5.8~\mu m}}$\textgreater $F_{\rm{8.0~\mu m}}$   & \textgreater23  & 65 \\
Lonsdale et al.\ (2008)                           &     61  & \textgreater400 & 819  &  $F_{\rm{3.6~\mu m}}$\textless $F_{\rm{4.5~\mu m}}$\textless $F_{\rm{5.8~\mu m}}$\textgreater $F_{\rm{8.0~\mu m}}$  & \textgreater23    & 55  \\
Farrah et al.\ (2008)            & 32  & \textgreater500  & 726 & $F_{\rm{3.6~\mu m}}$\textless $F_{\rm{4.5~\mu m}}$\textgreater $F_{\rm{5.8~\mu m}}$ and $F_{\rm{4.5~\mu m}}$\textgreater $F_{\rm{8.0~\mu m}}$    & \textgreater23    &  34  \\
Huang et al.\ (2009)$^{a}$             &      12  & \textgreater500 & 689 &                                                       0~\textless~[3.6]--[4.5]~\textless~0.4   &                   &   \\
                               &          & &                 &                                                    --0.7~\textless~[3.6]--[8.0]~\textless~0.5   &                   \\
Magliocchetti et~al.\ (2007)     &     793  & \textgreater350  & &                                                                                          & \textgreater25.5  & 200  \\
Yan et~al.\ (2005)               &      52  & \textgreater900  & &  $\log_{10}(\nu f_{\nu}(\rm{24~\mu m})/\nu {\textit f}_{\nu}(\rm{8~\mu m}))$~\textgreater~0.5      &                   &    \\
                               &          &                  & & $\log_{10}(\nu f_{\nu}(\rm{24~\mu m})/\nu {\textit f}_{\nu}(\rm{0.7~\mu m})$)~\textgreater~1.0  &                   &      \\\hline
\end{tabular}}
\par
\smallskip
$^{a}$ The sample of \citet{Huan08} differs by only one source from the one of \citet{Youn09}.
\end{table}