\begin{table}%t4
\caption{Number densities and emissivities of diffirent classes of sources.}
\label{emissivities}
%\centerline
{
\begin{tabular}{ccccc}
\hline
\hline
\multicolumn{1}{c}{Class} & 
\multicolumn{1}{c}{Space density above given luminosity} &
\multicolumn{3}{c}{Total emissivity ($10^{27}$~erg~s$^{-1}$~$\ms^{-1}$)}
\\
\multicolumn{1}{c}{} &
\multicolumn{1}{c}{ ($\ms^{-1}$)} &
\multicolumn{1}{c}{0.1--2.4~keV} &
\multicolumn{1}{c}{2--10~keV} &
\multicolumn{1}{c}{3--20~keV}
\\   
\hline
ABs         & $\sim$$1.2\times 10^{-2}$ ($\lx>10^{27.5}$~erg~s$^{-1}$) &
 $(14\pm 4)$ & $2.0\pm 0.8$ & $2.9\pm 1.3$\\  
CVs         & $(1.2\pm 0.3)\times 10^{-5}$ ($\lx>10^{31}$~erg~s$^{-1}$)
& $\la${\rm a few} & $1.1\pm 0.3$ & $2.4\pm 0.6$\\
ABs+CVs     & & $\sim$$15$        & $3.1\pm 0.8$  & $5.3\pm 1.5$\\
 YSs        & & $24\pm 3$        & $1.5\pm 0.4$  & $1.0\pm 0.2$\\
ABs+CVs+YSs & & $\sim$$40$        & $4.5\pm 0.9$  & $6.2\pm 1.5$\\
LMXBs   & $\sim$$3\times 10^{-9}$  ($\lx>10^{36}$~erg~s$^{-1}$) &
  $\sim$$40$$^{a}$ & $\sim$$90$$^{b}$    &   \\
\hline
\end{tabular}}
\medskip
$^{a}$ Emissivity in the 0.5--2~keV band extrapolated from
2--10~keV assuming a~power-law spectrum of photon index $\Gamma=1.56$,
as typical of~LMXBs with $10^{36}$~erg~s$^{-1}<\lx<10^{39}$~erg~s$^{-1}$ \citep{iab03}. \\
$^{b}$ The quoted 2--10~keV emissivity for LMXBs represents an~average over nearby galaxies \citep{gilfanov04}. 
\end{table}