The Radial Distribution of Galaxies in Λ Cold Dark Matter Clusters

We study the radial distribution of subhalos and galaxies usinghigh-resolution cosmological simulations of galaxy clusters formed in theconcordance LCDM cosmology. In agreement with previous studies, we find thatthe radial distribution of subhalos is significantly less concentrated thanthat of the dark matter, when subhalos are selected using their present-daygravitationally bound mass. We show that the difference in the radialdistribution is not a numerical artifact and is due to tidal stripping. Thesubhalos in the cluster core lose more than 70% of their initial mass sinceaccretion, while the average tidal mass loss for halos near the virial radiusis ~30%. This introduces a radial bias in the spatial distribution of subhaloswhen they are selected using their tidally truncated mass. We demonstrate thatthe radial bias disappears almost entirely if subhalos are selected using theirmass or circular velocity at the accretion epoch. The comparisons of theresults of dissipationless simulations to the observed distribution of galaxiesin clusters are therefore sensitive to the selection criteria used to selectsubhalo samples. Using the simulations that include cooling and starformation,we show that the radial distribution of subhalos is in reasonable agreementwith the observed radial distribution of galaxies in clusters for0.1

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