Galaxies and subhaloes in LCDM galaxy clusters

We combine 10 high resolution resimulations of cluster--sized dark haloes with semi--analytic galaxy formation modelling in order to compare the number density and velocity dispersion profiles of cluster galaxies with those of dark matter substructures (subhaloes). While the radial distribution of galaxies follows closely that of the dark matter, the distribution of dark matter subhaloes is much less centrally concentrated. The velocity dispersion profiles of galaxies are also very similar to those of the dark matter, while those for subhaloes are biased high, particularly in the inner regions of clusters. We explain how these differences, already clearly visible in earlier work, are a consequence of the formation of galaxies at the centres of dark matter haloes. Galaxies and subhaloes represent different populations and are not directly comparable. Evolution produces a complex and strongly position--dependent relation between galaxies and the subhaloes in which they reside. This relation can be properly modelled only by appropriate physical representation of the galaxy formation process.