of the identified features included in the simulation, are compared for wabs1 and wabs2. In Figure \[den\_dist2\] (bottom panel) we plot all the Ratios produced through identification of lines (239) using the [trunk-1]{} model and the absorber wabs1 ($\log \xi=2.08$, $N_H=10^{22}$ , $n_H=10^{12}$ ). A wavelength-color map has been placed at the right side, so one can read which lines are causing the deviations from 1, that is obtained when ${\rm EW}_{\rm meas}={\rm EW}_{\rm theo}$. It is natural from this plot to infer what is the spectrum that matches better the observation, i.e., the one with the smaller standard deviation (SD, top axis on the plot) from the mean equal to 1.

The same type of graphics has been plotted in Figure \[den\_dist1\] for wabs2 ($\log \xi=1.15$, $N_H=10^{21}$ , $n_H=10^{12}$ ), where again we reach the conclusion that the best-fit $n_H$ is the one with smallest SD for Ratio, with mean 1. An analysis of these results will be given in the next section.

COG analysis {#cog-analysis .unnumbered}
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In order for a line to be used as density diagnostic, it must be not saturated, and its ratio with measured EWs sensitive respect to $n_H$. In Figure \[den\_dist1\] we present 