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Stellar metallicity distribution functions (MDF) have been measured forresolved stellar populations in the outer halos of many galaxies in nearbygroups. Among them, the MDF of NGC 5128, the central giant elliptical in theCentaurus group, provides essential constraints for theories of massive galaxyformation and hierarchical assembly. To investigate the formation and chemicalevolution history of the outer halo of giant elliptical galaxies, we examinethe chemical properties of three zoom-in high resolution cosmologicalhydrodynamical simulations of an NGC 5128-like giant elliptical galaxy andcompare their outer halo MDFs to the observed one of NGC 5128. Even though thesimulated galaxies have different merging histories and age distributions, allpredicted MDFs are in good qualitative agreement with the observed one. Themedian metallicity of the simulated galaxies is on average $\rm [M/H]=-0.41 \pm0.06$ compared to the observed value of $\rm [M/H]=-0.38 \pm 0.02$ for NGC5128, and the dispersion in metallicity is $\sim 0.77$ dex for both observedand simulated galaxies. We investigate the origin of the stars ending up in theouter halo field of simulated galaxies and show that most have an `accreted'origin, formed in other small galaxies and later accreted in mergers. Only$\sim 15$ percent of the stars are formed `in situ' within the main progenitorof galaxy and radially migrate outwards. We show that the contribution ofmetal-rich in situ stars is sub-dominant in the outer halos of our simulatedgalaxies, but can be prominent in the inner regions.

The Metallicity Distribution Function in Outer Halo Fields of Simulated Elliptical Galaxies Compared to Observations of NGC 5128