\begin{table}%t1
%\centering
\par
\begin{tabular}{lccccc}
\hline
\hline\noalign{\smallskip}
Telescope & Beam (arcmin) & $D$ (beam 25~kpc) & Beam at $D=6$~Mpc & RMS (25 km s$^{-1}$) & $N_{\rm HI}$ (25 km s$^{-1}$) \\
\hline\noalign{\smallskip}
Parkes  & 15.5$'$  & 6~Mpc & 25~kpc & 1.1   mJy/Beam  &  $3.4 \times 10^{16}$~cm$^{-2}$  \\
Arecibo & 3.5$'$ & 25~Mpc & 6.1~kpc & 0.45  mJy/Beam  &  $2.9 \times 10^{17}$~cm$^{-2}$\\
ASKAP   & 3$'$ & 28~Mpc & 5.2~kpc & 0.3  mJy/Beam  &  $2.6 \times 10^{17}$~cm$^{-2}$\\
SKA     & 2.5$'$  & 33~Mpc & 4.4~kpc & 0.015 mJy/Beam  &  $1.8 \times 10^{16}$~cm$^{-2}$\\
\par
\hline
\end{tabular}
\caption{\label{mock_data}Sensitivity limits for four different telescopes 
  for an assumed line-width of 25~km~s$^{-1}$ after a total integration time of
  500~h to image an area of 30~square degrees.}
\end{table}