http://arxiv.org/abs/1709.06399
Shell galaxies are believed to form through the collision of a dwarf galaxy with an elliptical galaxy. Shell structures and kinematics have been noticed to be independent tools to measure the gravitational potential of the shell galaxies. In this work, as it is missing in the literature, we compare theoretically the formation of shells in Type I shell galaxies in different gravity theories, including Newtonian plus dark halo gravity, and two non-Newtonian gravity models, MOG and MOND in identical initial systems. We investigate the effect of dynamical friction, which by slowing down the dwarf galaxy in the dark halo models, limits the range of shell radii to small values. Under the same initial conditions, shells appear on a smaller time-scale and over a smaller range of distances in the presence of dark matter compared to the corresponding non-Newtonian gravity models. If galaxies are embedded in dark matter halo, then the merging time may be too rapid to allow multi-generation shell formation as required by observed systems due to the large dynamical friction effect. Starting from the same initial state, in the dark halo model the observation of small bright shells should be accompanied by large faint ones, while in the absence of dark matter the next shell generation patterns iterate with a specific time delay. The first shell generation pattern shows a degeneracy with the age of the shells and different theories, but the relative distance of the shells and the shell expansion velocity can break this degeneracy.
H. Vakili, P. Kroupa and S. Rahvar
Wed, 20 Sep 17
7/57
Comments: 14 pages, 10 figures, accepted for publication in ApJ