\begin{table}%t2
\caption{\label{tab:Systematics_gas}Best-fit transport parameters for different ISM.}
%\centering
\par
\begin{tabular}{ccccccc} \hline\hline\noalign{\smallskip}
\multicolumn{2}{c}{Gas} & $K_0^{\rm best}\times 10^2$ & $\delta^{\rm best}$ &  $V_{\rm c}^{\rm best}$  &  $V_{\rm a}^{\rm best}$  & $\chi^2$/d.o.f.   \\
$\Sigma$   & $f_{\rm H}$ & (kpc$^2~$Myr$^{-1}$) &  &  (km$\;$s$^{-1}$)  & (km$\;$s$^{-1}$)   & \\\hline
& \multicolumn{1}{c}{} \vspace{-0.20cm} \\ 
${\it \Sigma^{\rm ref}}$ & ${\it f^{\rm ref}_{\rm H}}$                                     & {\it 0.48} & {\it 0.86} & {\it 18.8} & {\it 38.0} & {\it 1.47}    \vspace{0.15cm}\\  %chi2=39.7018 (31)
$\Sigma^{\rm ref}$ & $95\%$ & 0.53 & 0.83 & 18.6 & 38.1 & 1.24    \vspace{0.00cm}\\  %chi2=33.6148 (31)
$\Sigma^{\rm ref}$ & $80\%$ & 0.41 & 0.90 & 19.3 & 37.7 & 2.14    \vspace{0.15cm}\\  %chi2=57.7705 (31)
$\frac{1}{2}~\Sigma^{\rm ref}$ & $f^{\rm ref}_{\rm H}$                              & 0.25 & 0.85 & 9.5  & 19.4 & 1.45    \vspace{0.00cm}\\  %chi2=39.1246 (31)
$2~\Sigma^{\rm ref}$&$f^{\rm ref}_{\rm H}$                                        & 0.92 & 0.86 & 37.3 & 74.6 & 1.51    \vspace{0.10cm}\\  %chi2=40.6841 (31)
% N.B.: 161 steps between 0.05 and 5000 GeV/n used
\hline
\end{tabular}
\tablefoot{Model III for $L=4$~kpc. For all settings, we keep fixed $\langle
n_{{\rm e}^{-}}\rangle=0.033$ and $T_{\rm e}\sim 10^4$~K. The reference parameters for the surface density
$\Sigma^{\rm ref}$ and the hydrogen fraction $f^{\rm ref}_{\rm H}$ are given
in Table~\ref{tab:default}.}
\end{table}