Dark matter mass fraction in gal. through X-ray gas

We suggest that this higher level may be a consequence of sparse stellar haloes and quieter histories with fewer major episodes of feedback or mergers. Comparisons are made with the Magneticum Pathfinder suite of simulations for both normal and centrally dominant "Brightest Cluster" galaxies. Though the observed data exhibit somewhat larger scatter at a given galaxy mass than do the simulations, the mean level of DM mass fraction for all classes of galaxies is in good first-order agreement with the simulations.

Finally, we find that the group galaxies with stellar masses near M_*_~10^11^M_{sun}_ have relatively more outliers at low f5 than in other mass ranges, possibly the result of especially effective AGN feedback in that mass range leading to expansion of their DM halos.