Roche lobe shapes for testing MOND-like modified gravities

Zhao, Hongsheng; Tian, Lanlan

doi:10.1051/0004-6361:20054379

Cited by 43 publications

(57 citation statements)

References 32 publications

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“…As a result of the nonlinearity of this formulation, the strong equivalence principle is violated in MOND when considering the external field in which a system is embedded (e.g. Bekenstein & Milgrom (1984); Zhao & Tian (2006); Sánchez-Salcedo & Hernandez (2007); Famaey & McGaugh (2012)). This implies that the internal gravitational dynamics of a system embedded in an external field depends on both the internal and external gravitational field.…”

Section: Introductionmentioning

confidence: 99%

Declining rotation curves of galaxies as a test of gravitational theory

Haghi

Bazkiaei

Zonoozi

et al. 2016

Mon. Not. R. Astron. Soc.

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Unlike Newtonian dynamics which is linear and obeys the strong equivalence principle, in any nonlinear gravitation such as Milgromian dynamics (MOND), the strong version of the equivalence principle is violated and the gravitational dynamics of a system is influenced by the external gravitational field in which it is embedded. This so called External Field Effect (EFE) is one of the important implications of MOND and provides a special context to test Milgromian dynamics. Here, we study the rotation curves (RCs) of 18 spiral galaxies and find that their shapes constrain the EFE. We show that the EFE can successfully remedy the overestimation of rotation velocities in 80% of the sample galaxies in Milgromian dynamics fits by decreasing the velocity in the outer part of the RCs. We compare the implied external field with the gravitational field for non-negligible nearby sources of each individual galaxy and find that in many cases it is compatible with the EFE within the uncertainties. We therefore argue that in the framework of Milgromian dynamics, one can constrain the gravitational field induced from the environment of galaxies using their RCs. We finally show that taking into account the EFE yields more realistic values for the stellar mass-to-light ratio in terms of stellar population synthesis than the ones implied without the EFE.

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Section: Introductionmentioning

confidence: 99%

Declining rotation curves of galaxies as a test of gravitational theory

Haghi

Bazkiaei

Zonoozi

et al. 2016

Mon. Not. R. Astron. Soc.

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“…This attribute implies a violation of the strong equivalence principle and is usually referred to as the external field effect (Milgrom 1983b). The impact of external fields has been studied for a variety of different situations, including the motion of probes in the inner solar system (Milgrom 2009), the Roche lobe of binary stars (Zhao & Tian 2006), the kinetics of stars in globular clusters (Milgrom 1983b;Perets et al 2009), the escape speeds and truncations of galactic rotation curves (Wu et al 2007), satellites surrounding a host galaxy (Brada & Milgrom 2000;Angus 2008), and the phase transition of distant star clusters moving towards the galactic centre (Wu & Kroupa 2013). …”

Section: Introductionmentioning

confidence: 99%

Lopsidedness of Self-consistent Galaxies Caused by the External Field Effect of Clusters

Wang

Feix

et al. 2017

ApJ

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Adopting Schwarzschild's orbit-superposition technique, we construct a series of self-consistent galaxy models, embedded in the external field of galaxy clusters in the framework of Milgrom's MOdified Newtonian Dynamics. These models represent relatively massive ellipticals with a Hernquist radial profile at various distances from the cluster centre. Using N -body simulations, we perform a first analysis of these models and their evolution. We find that self-gravitating axisymmetric density models, even under a weak external field, lose their symmetry by instability and generally evolve to triaxial configurations. A kinematic analysis suggests that the instability originates from both box and non-classified orbits with low angular momentum. We also consider a self-consistent isolated system which is then placed in a strong external field and allowed to evolve freely. This model, just as the corresponding equilibrium model in the same external field, eventually settles to a triaxial equilibrium as well, but has a higher velocity radial anisotropy and is rounder. The presence of an external field in MOND universe generically predicts some lopsidedness of galaxy shapes.

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“…In the latter case, either gravity should be modified [24,25], which could lead to some subtle differences regarding e.g. dynamical friction [26,27] or tides [28,29], or inertia should be modified [21,30,31], which would lead to very significant differences with the DM interpretation, especially in non-stationary situations [21].…”

Section: Introductionmentioning

confidence: 99%

Insight into the baryon-gravity relation in galaxies

Famaey

Gentile²,

Bruneton³

et al. 2007

Phys. Rev. D

121

149

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Observations of spiral galaxies strongly support a one-to-one analytical relation between the inferred gravity of dark matter at any radius and the enclosed baryonic mass. It is baffling that baryons manage to settle the dark matter gravitational potential in such a precise way, leaving no "messy" fingerprints of the merging events and "gastrophysical" feedbacks expected in the history of a galaxy in a concordance Universe. This correlation of gravity with baryonic mass can be interpreted from several non-standard angles, especially as a modification of gravity called TeVeS, in which no galactic dark matter is needed. In this theory, the baryon-gravity relation is captured by the dieletric-like function µ of Modified Newtonian Dynamics (MOND), controlling the transition from 1/r 2 attraction in the strong gravity regime to 1/r attraction in the weak regime. Here, we study this µ-function in detail. We investigate the observational constraints upon it from fitting galaxy rotation curves, unveiling the degeneracy between the stellar mass-to-light ratio and the µ-function as well as the importance of the sharpness of transition from the strong to weak gravity regimes. We also numerically address the effects of non-spherical baryon geometry in the framework of non-linear TeVeS, and exhaustively examine how the µ-function connects with the free function of that theory. In that regard, we exhibit the subtle effects and wide implications of renormalizing the gravitational constant. We finally present a discontinuity-free transition between quasi-static galaxies and the evolving Universe for the free function of TeVeS, inevitably leading to a return to 1/r 2 attraction at very low accelerations in isolated galaxies.

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Roche lobe shapes for testing MOND-like modified gravities

Cited by 43 publications

References 32 publications

Declining rotation curves of galaxies as a test of gravitational theory

Declining rotation curves of galaxies as a test of gravitational theory

Lopsidedness of Self-consistent Galaxies Caused by the External Field Effect of Clusters

Insight into the baryon-gravity relation in galaxies

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