MOND Prediction for the Velocity Dispersion of the `Feeble Giant' Crater II

Stacy S. McGaugh

doi:10.3847/2041-8205/832/1/L8

paper

MOND Prediction for the Velocity Dispersion of the `Feeble Giant' Crater II

arXiv:1610.06189 · doi:10.3847/2041-8205/832/1/L8

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 ( $g_{in} \approx 34 km^{2} s^{- 2} kpc^{- 1} ≪ a_{0} = 3700 km^{2} s^{- 2} kpc^{- 1}$ ). Despite its great distance ( $\approx 120$ kpc) from the Milky Way, the external field of the host ( $g_{e x} \approx 282 km^{2} s^{- 2} kpc^{- 1}$ ) 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: $σ_{e f e} = 2. 1_{- 0.6}^{+ 0.9} km s^{- 1}$ .

5 pages, no figures. Minor changes made for consistency with the version accepted for publication in ApJ Letters. My expectation for the velocity dispersion in LCDM is 17 km/s. Other predictions are solicited

MOND Prediction for the Velocity Dispersion of the `Feeble Giant' Crater II

Abstract

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