Lessons from the Local Group (and Beyond) on Dark Matter: A Conference in honour of David Block and Bruce Elmegreen
Abstract
The existence of exotic dark matter particles outside the standard model of particle physics constitutes a central hypothesis of the current standard model of cosmology (SMoC). Using a wide range of observational data I outline why this hypothesis cannot be correct for the real Universe. Assuming the SMoC to hold, (i) the two types of dwarf galaxies, the primordial dwarfs with dark matter and the tidal dwarf galaxies without dark matter, ought to present clear observational differences. But in fact there is no observational evidence for two separate families of dwarfs, neither in terms of their location relative to the baryonic Tully-Fisher relation nor in terms of their radius-mass relation. This result is illuminated by the arrangements of the satellite galaxies around host galaxies for which we have data: the arrangements in rotating disk-of-satellites, in particular around the Milky Way and Andromeda, has been found to be only consistent with most if not all dwarf satellite galaxies being tidal dwarf galaxies. The predicted large numbers of independently or in-group accreted, dark-matter-dominated primordial dwarfs are most inconspicuously absent around the Milky Way in particular. The highly symmetric structure of the entire Local Group too is inconsistent with its galaxies stemming from a stochastic merger-driven hierarchical buildup over cosmic time. (ii) Dynamical friction on the expansive and massive dark matter halos is not evident in the data: the satellite galaxies of the Milky Way with proper motion measurements have no infall solutions as they would merge with the MW if they have dark matter halos, and galaxy groups such as the M81 group are found to not merge on the short time scales implied if each galaxy has a dark matter halo. Taking the various lines of evidence together, the hypothesis that dynamically relevant exotic dark matter exists needs to be firmly rejected.
- Publication:
-
Lessons from the Local Group: A Conference in honor of David Block and Bruce Elmegreen
- Pub Date:
- 2015
- DOI:
- 10.1007/978-3-319-10614-4_28
- arXiv:
- arXiv:1409.6302
- Bibcode:
- 2015llg..book..337K
- Keywords:
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- Physics;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 13 pages, 2 figures, invited presentation, accepted for publication in Seychelles conference on galaxy evolution, "Lessons from the Local Group", ed. K. C. Freeman, B. G. Elmegreen, D. L. Block, and M. Woolway (Dordrecht: Springer), in press, 2014