David F. Mota, Vincenzo Salzano, Salvatore Capozziello, Nicola R. Napolitano
We investigate the gravitational effect of a scalar field within scalar-tensor gravity as an alternative of the dark matter. Motivated by results of chameleon models, $f(R)$ gravity and symmetron models, we study a phenomenological scenario where the scalar field has a mass and a coupling constant to the ordinary matter which scale with the local properties of the considered astrophysical system. We analyze the compatibility of this "alternative gravity" scenario at galaxy and galaxy cluster scales. Main results are: 1) the velocity dispersion of elliptical galaxies can be fit remarkably well by a scalar field, with model significance similar to the one obtained if a classical Navarro-Frenk-White dark halo profile is considered; 2) in particular, the analysis of the stellar dynamics and the gas equilibrium on elliptical galaxies has shown that the scalar field can couple with ordinary matter with different strength (different coupling constants) depending on the clustering state of matter components; 3) spiral galaxies and clusters of galaxies combined together show evident correlations among theory parameters (coupling constants and scalar field interaction length) which suggests the generality of the results at all scales and the way toward an unification of the theory for all gravitating systems; 4) the gravitational effects of the scalar field and its viability as an alternative to the dark matter are confirmed by some preliminary test on strong lensing at galaxy cluster scales.
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http://arxiv.org/abs/1211.1019
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