http://arxiv.org/abs/1903.10849
We explore the mass of the Local Group via the use of the simple, dynamical `timing argument’ in the context of a variety of theories of dark energy and modified gravity: a cosmological constant, a perfect fluid with constant equation of state $w$, quintessence (minimally coupled scalar field), MOND, and symmetrons (coupled scalar field). We explore generic coupled scalar field theories, with the symmetron model as an explicit example. We find that theories which attempt to eliminate dark matter by using flat rotation curves produce mass estimates in the timing argument which are not compatible with the luminous mass of the galaxies alone. Assuming that the galaxies are on a first pass, MOND gives of around $3\times 10^{10} M_\odot$, roughly 10\% of the luminous mass of the LG, although a higher mass can be obtained in the case of a previous fly-by event between the MW and M31. The symmetron model suggests a mass too high to be explained without additional dark matter ($\mathcal{O}(10^{12}) M_\odot$). We also demonstrate that tensions in measurements of $H_0$ can produce an uncertainty in the Local Group mass estimate comparable to observational uncertainties on the separation and relative velocity of the galaxies, with values for the mass ranging from $4.55 – 5.43 \times 10^{12} M_{\odot}$ varying $h$ between 0.67 and 0.76.
M. McLeod and O. Lahav
Wed, 27 Mar 19
73/74
Comments: 22 pages, 6 figures, 2 tables
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