Testing modified gravity with dwarf spheroidal galaxies

Abstract

The observed velocity dispersion of the classical dwarf spheroidal (dSph) galaxies of the Milky Way (MW) requires the Newtonian stellar mass-to-light ($M_{\ast }/L$) ratios in the range of about 10 to more than 100 solar units that are well outside the acceptable limit predicted by stellar population synthesis models. Using Jeans analysis, we calculate the line-of-sight velocity dispersion (${\sigma }_{\text{los}}$) of stars in eight MW dSphs in the context of the modified gravity (MOG) theory of Moffat, assuming a constant $M_{\ast }/L$ ratio without invoking the exotic cold dark matter. First, we use the weak field approximation of MOG and assume the two parameters $\alpha$ and $\mu$ of the theory to be constant as has already been inferred from fitting to the observed rotational data of The HI Nearby Galaxy Survey catalogue of galaxies. We find that the derived $M_{\ast }/L$ ratios for almost all dSphs are too large to be explained by the stellar population values. In order to fit the line-of-sight velocity dispersions of the dSph with reasonable $M_{\ast }/L$ values, we must vary $\alpha$ and $\mu$ on a case by case basis. A common pair of values cannot be found for all dSphs. Comparing with the values found from rotation curve fitting, it appears that $\mu$ correlates strongly with galaxy luminosity, shedding doubt on it as a universal constant.

9 pages, 5 figures, 2 tables, Accepted for publication in MNRAS

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• The Bullet Cluster 1E0657-558 evidence shows Modified Gravity in the absence of Dark Matter
• Testing modified gravity with globular cluster velocity dispersions
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• Jeans analysis in modified gravity
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Cited by in corpus (6)

• Dark matters on the scale of galaxies
• Stellar streams as gravitational experiments II. Asymmetric tails of globular cluster streams
• The cusp-core problem in gas-poor dwarf spheroidal galaxies
• Giant low-surface-brightness dwarf galaxy as a test bench for MOdified Gravity
• Local Stability of Galactic Discs in Modified Dynamics
• Dynamics of Dwarf Galaxies in Scalar-Tensor-Vector-Gravity