« Formation of Fornax dwarf spheroidal and the survival of its globular clusters «
The presence of globular clusters (GCs) in the Fornax dwarf spheroidal is an important test of the theories aiming to address the missing mass problem. The problem is that in most of them, the GCs are expected to sink in the center of Fornax due to dynamical friction much faster than the observed stellar ages of the GCs. I will present our assessment of the problem in the framework of MOND modified gravity using N-body simulations. Following older MOND studies of the Local Group, we assumed that Fornax is a tidal dwarf galaxy formed in a Milky Way – Andromeda flyby 7 Gyr ago. We newly propose that the GCs of Fornax started their lives as massive star clusters in the young Milky Way. Our results are the following: 1) The scenario can explain why the Milky Way has a disk of satellites, whose member Fornax is. 2) The simulations show that the probability that Fornax has five unsunk GCs as observed is 20%, which is not low enough to exclude MOND. 3) The simulations also explain why the GCs have the observed distribution of distances from Fornax. 4) For the latest proper motion, MOND gravity implies an orbit of Fornax whose perigalacticons perfectly agree with the observed peaks of star formation in Fornax. 5) Without any tuning, the simulations reproduce the observed « stellar halo » of Fornax. 6) A stellar stream is predicted to extend from Fornax which could be currently detectable. 7) By an additional simulation, we show that if Fornax stared its life as a rotating disky tidal dwarf galaxy, the varying tidal forces from the Milky Way were able to transform it into a non-rotating spheroidal.