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We show that a significant correlation (up to 5sigma) emerges between thebulge index, defined to be larger for larger bulge/disk ratio, in spiralgalaxies with similar luminosities in the Galaxy Zoo 2 of SDSS and the numberof tidal-dwarf galaxies in the catalogue by Kaviraj et al. (2012).  In the standard cold or warm dark-matter cosmological models the number ofsatellite galaxies correlates with the circular velocity of the dark matterhost halo. In generalized-gravity models without cold or warm dark matter sucha correlation does not exist, because host galaxies cannot capture in-fallingdwarf galaxies due to the absence of dark-matter-induced dynamical friction.However, in such models a correlation is expected to exist between the bulgemass and the number of satellite galaxies, because bulges and tidal-dwarfsatellite galaxies form in encounters between host galaxies. This is notpredicted by dark matter models in which bulge mass and the number ofsatellites are a priori uncorrelated because higher bulge/disk ratios do notimply higher dark/luminous ratios. Hence, our correlation reproduces theprediction of scenarios without dark matter, whereas an explanation is notfound readily from the a priori predictions of the standard scenario with darkmatter. Further research is needed to explore whether some application of thestandard theory may explain this correlation.

The number of tidal dwarf satellite galaxies in dependence of bulge index