\begin{table}%t1 
\caption{\label{tab_densitylaws}Density laws and associated parameters.  }
\small%\centering
\par
\begin{tabular}{lccc}
\hline\hline\noalign{\smallskip}
&Density law & Constants   & $\rho_{\rm c}$  \\
&            &  (kpc) & ($M_{\odot}~\rm pc^{-3}$) \\
\hline\noalign{\smallskip}
Bulge &${\rm e}^{-(r/r_{0})^{2}}$ &$r_{0}=0.5$ & $\frac{M_{\rm b}}{4\pi r_{0}^{3}}=12.73$ \\
\\
Thin disc &${\rm e}^{-R/h_{R}}\textrm{sech}^{2}(-z/h_{z})$ &$h_{R}=2.5$   & $\frac{M_{\rm tn}}{4\pi h_{R}^{2}h_{z}}=1.881$ \\
          &                                          &$h_{z}=0.352$ & \\
\\
Thick disc &${\rm e}^{-R/h_{R}}{\rm e}^{-z/h'_{z}}$ & $h_{R} = 2.5$  & $\frac{M_{\rm tk}}{4\pi h_{R}^{2}h'_{z}}=0.0286$\\
           &                            & $h'_{z}=1.158$ & \\
\\
Halo &$ [(1+(\frac{a}{a_{0}})^{2})]^{-1}$ &$a_{0} = 2.7$ & 0.108\\
\hline
\end{tabular}
\tablefoot{$r$ is the
spherical radius from the center of the Galaxy and $r_{0}$ is bulge
scale length; $R$ and $z$ are the natural cylindrical coordinates of
the axisymmetric disc, $h_{R}$ is the scale length of the disc,
$h_{z}$ is the scale height of the thin disc, $h'_{z}$ is the scale
height of the thick disc; $a$ is the radius of the halo and $a_{0}$
is a constant; $\rho_{\rm c}$ is the central mass density.}  
\end{table}