\begin{table}%t6
\caption{\label{table:ISM_oxygen}Ionic column densities of oxygen in $10^{22}$ m$^{-2}$.}             %%\centering
\par
\par
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\par
\begin{tabular}{lcccc}
\hline\hline\noalign{\smallskip}
X& Mod A$_{\rm sim}$\tablefootmark{a}  & Mod A\tablefootmark{a}  & Mod B\tablefootmark{b}  & Mod C\tablefootmark{c} \\ 
\hline
%\hline
\ion{O}{i}                              & 3.0                     &  3.1            &  2.9            & 2.7 \\
%\hline
\ion{O}{ii}, \ion{O}{iii}, \ion{O}{iv}  & $\equiv $0                       &  $\equiv $0             &  0.35           & 0.1 \\
%\hline
\ion{O}{vii}, \ion{O}{viii}             & $\equiv $0                      &  $\equiv $0              &  0.05           & 0.05 \\
%\hline
Dust                                    & $\equiv $0                       &  $\equiv $0              &  $\equiv $0              & 0.35 \\
\hline
%\hline
Total $N_{\rm O}$                       & 3.0                     &  3.1            &  3.3            & 3.2 \\
\hline
\end{tabular} 
\tablefoot{\tablefoottext{a}{Mono-phase gas (Table~\ref{table:rgs_fit} for the simultaneous EPIC-RGS fit).} 
\tablefoottext{b}{Three-phases gas (Table~\ref{table:rgs_fit}). $^{(c)}$ Gas + dust model (see Table~\ref{table:molecules}). {The agreement between the oxygen column densities estimated with different models validates our method.}}}\vspace*{-2mm}
\end{table}