Dark matter(?) in elliptical galaxies - particularly in NGC 3311
Intervenant : Tom Richtler
Modern concepts of gravity include gravity as an emergent entropic force, possibly leading to a new understanding of Modified Newtonian Dynamics (MOND) which governs the weak-field dynamics of galaxies, for example the baryonic Tully-Fisher relation (BTFR). The question whether elliptical galaxies fall onto the same BTFR as spiral galaxies, obviously is critical for the universal character of the MONDian phenomenology among galaxies and could act as a falsification of fundamental physics. Because the uncertainty of individual mass determinations is considerable, satisfactory answers are only expected from appropriate samples of nearby galaxies. The present literature on elliptical galaxy masses from dyanmical tracers does not give a clear-cut answer: some galaxies are MONDian, others apparently not. The largest deviations from the baryonic TF relation are found for central galaxes in clusters. I report on our work on NGC3311, the central galaxy in the Hydra I cluster. I argue that its massive cored dark halo found previously probably is a manifestion of the inhomogeneity of infalling tracer populations. Whether galaxy clusters are MONDian or not, still remains to be seen.