The Descendants of Lyman Break Galaxies in Galaxy Clusters: Spatial Distribution and Orbital Properties

We combine semianalytical methods with an ultra-high-resolution simulation of a cluster (of mass 2.3 × 10 14 h -1 M ☉ and 4 × 10 6 particles within its virial radius) formed in a standard cold dark matter universe to study the spatial distribution and orbital properties of the present-day descendents of Lyman break galaxies (LBGs). At redshift 3 we find on average a total of 12 halos containing at least one LBG in the region that will later collapse to form the cluster itself. At the present time only five of these halos survive as separate entities inside the cluster virial radius, having been stripped of most of their dark matter. Their circular velocities are in the range 200-550 km s -1 . Seven halos merged together to form the central object at the very center of the cluster. Using semianalytical modeling of galaxy evolution we show that descendents of halos containing the most massive LBGs now host giant elliptical galaxies such as those typically found in rich galaxy clusters. Inside the simulated cluster, galaxy orbits are very radial, with a pericenter-to-apocenter ratio of about 1 : 5. The orbital eccentricities of LBG descendents are statistically indistinguishable from those of the average galaxy population inside the cluster, suggesting that the orbits of these galaxies are not significantly affected by dynamical friction decay after the formation of the cluster's main body. In this cluster, possibly because of its early formation time, the descendents of massive LBGs are contained within the central 60% of the cluster virial radius and have an orbital velocity dispersion lower than the global galaxy population, originating a mild luminosity segregation for the brightest cluster members. Mass estimates based only on massive LBG descendents (especially including the central cD) reflect this bias in space and velocity and underestimate the total mass of this well-virialized cluster by up to a factor of 2 compared to estimates using at least 20 cluster members.