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

We combine semi–analytical methods with a ultra-high resolution simulation of a cluster (of mass 2.3 × 10hM⊙, and 4 × 10 6 particles within its virial radius) formed in a standard CDM universe to study the spatial distribution and orbital properties of the present–day descendents of Lyman Break galaxies (LBG). At redshift 3 we find a total of 12 halos containing at least one Lyman Break galaxy 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 virial radius, having been stripped of most of their dark matter. Their circular velocities are in the range 200 – 550 km/sec. Seven halos merged together to form the central object at the very center of the cluster. Using semi-analytical modeling of galaxy evolution we show that descendents of halos containing Lyman Break galaxies now host giant elliptical galaxies such as those typically found in rich galaxy clusters. All 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 due to its early formation time, the descendents of Lyman break galaxies 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 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 two compared to estimates using at least 20 cluster members. Subject headings: dark matter — cosmology: observations, theory — galaxies: clusters, formation