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

TL;DR

This study finds a significant correlation between bulge index and the number of tidal-dwarf galaxies in spiral galaxies, challenging standard dark matter models and supporting alternative gravity theories.

Contribution

It demonstrates a correlation between bulge index and satellite galaxies, providing evidence favoring models without dark matter over standard dark matter-based cosmology.

Findings

Significant correlation (up to 5sigma) between bulge index and tidal-dwarf galaxy count.

Correlation aligns with predictions of dark matter-free gravity models.

Challenges the standard dark matter paradigm's explanation of satellite galaxy distribution.

Abstract

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