MOND Prediction for the Velocity Dispersion of the `Feeble Giant' Crater II (1610.06189v2)

Published 19 Oct 2016 in astro-ph.GA

Abstract: Crater II is an unusual object among the dwarf satellite galaxies of the Local Group in that it has a very large size for its small luminosity. This provides a strong test of MOND, as Crater II should be in the deep MOND regime ($g_{in} \approx 34\;\mathrm{km}^{2\,\mathrm{s}^{{-2}\,\mathrm{kpc}^{-1}}} \ll a_0 = 3700\;\mathrm{km}^{2\,\mathrm{s}^{{-2}\,\mathrm{kpc}^{-1}$).}} Despite its great distance ($\approx 120$ kpc) from the Milky Way, the external field of the host ($g_{ex} \approx 282\; \mathrm{km}^{2\,\mathrm{s}^{{-2}\,\mathrm{kpc}^{-1}$)}} comfortably exceeds the internal field. Consequently, Crater II should be subject to the external field effect, a feature unique to MOND. This leads to the prediction of a very low velocity dispersion: $\sigma_{efe} = 2.1^{{+0.9}_{-0.6}\;\mathrm{km}\,\mathrm{s}^{-1}$.}