Understanding local dwarf spheroidals and their scaling relations under MOdified Newtonian Dynamics

Abstract

We use a specific form of the interpolation function in the MOND formalism, which optimally accounts for the internal structure of dwarf spheroidal (dSph) galaxies, to explore the consequences it has on the scaling relations seen in these systems. The particular form of the interpolation function we used leads to a law of gravity that does not degrade the good fit of the MOND proposal on galactic scales, and in fact, slightly improves the accordance with observations on dSph scales. This formalism yields a good description of gravitational phenomena without the need of invoking any still undetected and hypothetically dominant dark matter, in the weak field regime probed by local dSph galaxies. Isothermal equilibrium density profiles then yield projected surface density profiles for the local dSph galaxies in very good agreement with observational determinations, for values of the relevant parameters as inferred from recent observations of these Galactic satellites. The observed scaling relations for these systems are also naturally accounted for within the proposed scheme, including a previously unrecognised correlation of the inferred mass-to-light ratios of local dSph's with the ages of their stellar populations, which is natural in modified gravity schemes in the absence of dark matter. The results shed some light on the form that the MOND interpolating function may have in the most challenging regime, which occurs at moderate accelerations and intermediate mass-weighted lengths.

The Dark Matter Crisis: Falsification of the Current Standard Model of Cosmology

“…Rotation curves and large dynamical M/L ratia in MW satellites may also be explained by non-Newtonian theories (e.g. Brada & Milgrom 2000;Angus 2008;McGaugh & Wolf 2010;Hernandez et al 2010;Famaey & McGaugh 2012) and tidal effects (Kroupa 1997), so large dynamical M/L values do not have a unique fundamental solution.…”

Local-Group tests of dark-matter concordance cosmology

“…Both the MOND and MOG approaches have been applied to the satellite galaxy problem with appreciable success (Milgrom 1995;Brada & Milgrom 2000;Angus 2008;Moffat & Toth 2008;Hernandez et al 2010;McGaugh & Wolf 2010). It has already been conclusively demonstrated that spiral galaxy rotation curves are well recovered in MOND purely by the baryon distribution without any parameter adjustments (Sanders & McGaugh 2002;McGaugh 2004McGaugh , 2005aSanders & Noordermeer 2007), and MOG is reported to also do well on this account (Brownstein & Moffat 2006).…”

A Phase Space Diagram for Gravity

“…Systems having extents larger than their corresponding r M values will be in the dark matter mimicking regime, while those smaller than this value will be in the Newtonian regime, provided equilibrium velocities satisfy v << c, e.g., [25,26]. The appearance of a critical mass dependent length scale is not new to gravity; in the covariant version of Newtonian gravity, general relativity, the introduction of a critical velocity, c, introduces a corresponding critical mass dependent length scale r S = 2GM/c 2 .…”