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We used adaptive mesh refinement hydrodynamic cosmological simulations of a$z=1$ Milky Way-type galaxy and a $z=0$ Dwarf galaxy and generated syntheticquasar absorption-line spectra of their circumgalactic medium (CGM). Our goalis to assess whether standard observational spectroscopic analysis methodsaccurately reproduce intrinsic column densities, metallicities [Si/H], andhydrogen densities $n_{H}$, in simulated absorption-line systems. Withoutknowledge of the intrinsic simulated properties (blind study), we analysedsynthetic COS and HIRES spectra with fixed $S/N=30$ to determine the columndensities, metallicity, and $n_{H}$, using Voigt profile fitting combined withMarkov-Chain Monte-Carlo single-phase {\sc Cloudy} modelling techniques. Toquantify the intrinsic simulated absorbing gas properties, we objectivelydetermined which gas cells along a line of sight (LOS) contribute to detectedabsorption in the spectra and adopt the unweighted geometric mean of these gascell properties. For this pilot study, we performed this experiment for fiveLOS in the Milky-Way galaxy and five LOS in the Dwarf galaxy. We found anaverage agreement between the "observed" and intrinsic metallicityoverestimated within $0.8\sigma$ or $0.2$ dex for the "Milky-Way"' CGM andoverestimated within $1.4\sigma$ or $0.2$ dex for the Dwarf galaxy CGM. Wefound that the spectroscopically-derived $n_{H}$ are underestimated within$0.8\sigma$ or $0.4$ dex of the intrinsic $n_{H}$ for the "Milky-Way" CGM andoverestimated within $0.3\sigma$ or $0.3$ dex for the Dwarf galaxy CGM. Theoverall agreement suggests that, for single-phase ionisation modelling ofsystems where there is substantial spread in gas properties, global metallicitymeasurements from quasar absorption line studies are capturing the averagemetallicity and ionisation parameters in a given astrophysical environment.

Using cosmological simulations and synthetic absorption spectra to assess the accuracy of observationally derived CGM metallicities