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

References in corpus (25)

• Evolutionary population synthesis: models, analysis of the ingredients and application to high-z galaxies
• A Universal Mass Profile for Dwarf Spheroidal Galaxies?
• Scalar-Tensor-Vector Gravity Theory
• The Observed properties of Dark Matter on small spatial scales
• Galaxy Rotation Curves Without Non-Baryonic Dark Matter
• Velocity Dispersion Profiles of Seven Dwarf Spheroidal Galaxies
• The Milky Way's satellite population in a LambdaCDM universe
• The Mass Discrepancy-Acceleration Relation: Disk Mass and the Dark Matter Distribution
• The MOG weak field approximation and observational test of galaxy rotation curves
• The Bullet Cluster 1E0657-558 evidence shows Modified Gravity in the absence of Dark Matter
• Galaxy Cluster Masses Without Non-Baryonic Dark Matter
• Testing modified gravity with globular cluster velocity dispersions
• Dwarf Spheroidals in MOND
• Fundamental parameter-free solutions in Modified Gravity
• Dwarf-spheroidal satellites: are they of tidal origin?
• Declining rotation curves of galaxies as a test of gravitational theory
• Galactic rotation curves, the baryon-to-dark-halo-mass relation and space-time scale invariance
• Testing fundamental physics with distant star clusters: theoretical models for pressure-supported stellar systems
• Jeans analysis in modified gravity
• Observed Properties of Dark Matter: dynamical studies of dSph galaxies
• Cosmological observations in a modified theory of gravity (MOG)
• N-body simulations of the Carina dSph in MOND
• Distant star clusters of the Milky Way in MOND
• Spherical Collapse in Modified Newtonian Dynamics (MOND)
• Observational Constraints on the Modified Gravity Model (MOG) Proposed by Moffat: Using the Magellanic System

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• Stellar streams as gravitational experiments II. Asymmetric tails of globular cluster streams
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• On the cosmology of scalar-tensor-vector gravity theory
• The cusp-core problem in gas-poor dwarf spheroidal galaxies
• On the gravitational instability in the Newtonian limit of MOG
• Testing MOG, Non-Local Gravity and MOND with rotation curves of dwarf galaxies
• Global stability of self-gravitating disks in modified gravity
• 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