The Globular Cluster NGC 2419: A Crucible for Theories of Gravity

Ibata, Rodrigo; Sollima, A.; Nipoti, Carlo; Bellazzini, M.; Chapman, Scott; Dalessandro, E.

doi:10.1088/0004-637x/738/2/186

Cited by 108 publications

(168 citation statements)

References 72 publications

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“…It is therefore possible to see that our nonlocal as well as nonlinear modification of Newtonian gravity cannot behave as in the Modified Newtonian Dynamics (MOND) approach to the breakdown of Newtonian gravity [21][22][23]. From the scaling property of our modified…”

Section: B Nonlinear Kernelmentioning

confidence: 97%

Nonlocal gravity: Modified Poisson's equation

Chicone

Mashhoon

2012

Journal of Mathematical Physics

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The recent nonlocal generalization of Einstein's theory of gravitation reduces in the Newtonian regime to a nonlocal and nonlinear modification of Poisson's equation of Newtonian gravity. The nonlocally modified Poisson equation implies that nonlocality can simulate dark matter. Observational data regarding dark matter provide limited information about the functional form of the reciprocal kernel, from which the original nonlocal kernel of the theory must be determined. We study this inverse problem of nonlocal gravity in the linear domain, where the applicability of the Fourier transform method is critically examined and the conditions for the existence of the nonlocal kernel are discussed. This approach is illustrated via simple explicit examples for which the kernels are numerically evaluated. We then turn to a general discussion of the modified Poisson equation and present a formal solution of this equation via a successive approximation scheme. The treatment is specialized to the gravitational potential of a point mass, where in the linear regime we recover the Tohline-Kuhn approach to modified gravity.

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Section: B Nonlinear Kernelmentioning

confidence: 97%

Nonlocal gravity: Modified Poisson's equation

Chicone

Mashhoon

2012

Journal of Mathematical Physics

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“…This has led to tensions with MOND, especially in the case of Pal 14 (Jordi et al 2009) and Pal 4 (Frank et al 2012). GCs with a weak external field and extended velocity dispersion profiles, such as NGC 2419, display similar tensions (Ibata et al 2011), but see also Gentile et al (2010) and Sanders (2012). Note however that, in theories like those of Berezhiani & Khoury (2015), such tensions would be expected since MOND would only be an effective description of gravity within a given distance from the host galaxy (∼100 kpc in the case of the MW).…”

Section: Mondmentioning

confidence: 99%

“…This paradigm provides a natural explanation to the apparent conspiracy between the observed baryonic distribution and the gravitational force in various types of galaxies (see, e. g. Famaey & McGaugh 2012;McGaugh et al 2016;Lelli et al 2016). Nevertheless, the successes of the paradigm are mostly limited to galactic scales (for problems at other scales, see, e.g., Skordis et al 2006;Clowe et al 2006;Angus 2008;Ibata et al 2011;Dodelson 2011;Clowe et al 2012;Harvey et al 2015). This could mean that it is either an effective way to predict how dark matter (DM) is arranged in galaxies, or that it is an effective modification of gravity resulting from a broader theory of the dark sector (e.g.…”

Section: Introductionmentioning

confidence: 99%

Stellar streams as gravitational experiments

Thomas

Famaey

Ibata

et al. 2018

A&A

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Kinematically cold tidal streams of globular clusters (GC) are excellent tracers of the Galactic gravitational potential at moderate Galactocentric distances, and can also be used as probes of the law of gravity on Galactic scales. Here, we compare for the first time the generation of such streams in Newtonian and Milgromian gravity (MOND). We first compute analytical results to investigate the expected shape of the GC gravitational potential in both frameworks, and we then run N-body simulations with the Phantom of Ramses code. We find that the GCs tend to become lopsided in MOND. This is a consequence of the external field effect which breaks the strong equivalence principle. When the GC is filling its tidal radius the lopsidedness generates a strongly asymmetric tidal stream. In Newtonian dynamics, such markedly asymmetric streams can in general only be the consequence of interactions with dark matter subhalos, giant molecular clouds, or interaction with the Galactic bar. In these Newtonian cases, the asymmetry is the consequence of a very large gap in the stream, whilst in MOND it is a true asymmetry. This should thus allow us in the future to distinguish these different scenarios by making deep observations of the environment of the asymmetric stellar stream of Palomar 5. Moreover, our simulations indicate that the high internal velocity dispersion of Palomar 5 for its small stellar mass would be natural in MOND.

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“…The observations were performed with an exposure time of 600 s, securing S/N ∼ 50-60 spectra for the brightest targets and achieving S/N ∼ 15-20 for the faintest ones (I ∼ 17). The spectra have been reduced by means of the package developed for an optimal reduction and extraction of DEIMOS spectra and described in Ibata et al (2011).…”

Section: The Samplementioning

confidence: 99%

Chemical and Kinematical Properties of Galactic Bulge Stars Surrounding the Stellar System Terzan 5

Massari¹,

Mucciarelli²,

Ferraro³

et al. 2014

ApJ

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As part of a study aimed at determining the kinematical and chemical properties of Terzan 5, we present the first characterization of the bulge stars surrounding this puzzling stellar system. We observed 615 targets located well beyond the tidal radius of Terzan 5 and found that their radial velocity distribution is well described by a Gaussian function peaked at v rad = +21.0 ± 4.6 km s −1 with dispersion σ v = 113.0 ± 2.7 km s −1 . This is one of the few high-precision spectroscopic surveys of radial velocities for a large sample of bulge stars in such a low and positive latitude environment (b = +1.• 7). We found no evidence of the peak at v rad ∼ +200 km s −1 found in Nidever et al. Strong contamination of many observed spectra by TiO bands prevented us from deriving the iron abundance for the entire spectroscopic sample, introducing a selection bias. The metallicity distribution was finally derived for a subsample of 112 stars in a magnitude range where the effect of the selection bias is negligible. The distribution is quite broad and roughly peaked at solar metallicity ([Fe/H] +0.05 dex) with a similar number of stars in the super-solar and in the sub-solar ranges. The population number ratios in different metallicity ranges agree well with those observed in other low-latitude bulge fields, suggesting (1)

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The Globular Cluster NGC 2419: A Crucible for Theories of Gravity

Cited by 108 publications

References 72 publications

Nonlocal gravity: Modified Poisson's equation

Nonlocal gravity: Modified Poisson's equation

Stellar streams as gravitational experiments

Chemical and Kinematical Properties of Galactic Bulge Stars Surrounding the Stellar System Terzan 5

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