Unifying static analysis of gravitational structures with a scale-dependent scalar field gravity as an alternative to dark matter

¹ Fisika Teorikoaren eta Zientziaren Historia Saila, Zientzia eta Teknologia Fakultatea, Euskal Herriko Unibertsitatea, 644 Posta Kutxatila, 48080 Bilbao, Spain
e-mail: vincenzo.salzano@ehu.es
² Institute of Theoretical Astrophysics, University of Oslo, 0315 Oslo, Norway
e-mail: D.F.Mota@astro.uio.no
³ Dipartimento di Fisica, Universita’ degli Studi di Napoli “Federico II” and INFN, Sezione di Napoli, Complesso Universitario di Monte S. Angelo, Via Cinthia, Edificio N, 80126 Napoli, Italy
e-mail: capozzie@na.infn.it
⁴ INAF − Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
e-mail: napolita@na.astro.it

Received: 8 January 2013
Accepted: 7 November 2013

Abstract

Aims. We investigated the gravitational effects of a scalar field within scalar-tensor gravity as an alternative to dark matter. Motivated by chameleon, symmetron, and f(R)-gravity models, we studied a phenomenological scenario where the scalar field has both a mass (i.e. interaction length) and a coupling constant to the ordinary matter that scale with the local properties of the considered astrophysical system.

Methods. We analysed the feasibility of this scenario using the modified gravitational potential obtained in its context and applied it to the galactic and hot gas/stellar dynamics in galaxy clusters and elliptical/spiral galaxies respectively. This is intended to be a first step in assessing the viability of this new approach in the context of “alternative gravity” models.

Results. The main results are 1. the velocity dispersion of elliptical galaxies can be fitted remarkably well by the suggested scalar field, with model significance similar to a classical Navarro-Frenk-White dark halo profile; 2. the analysis of the stellar dynamics and the gas equilibrium in elliptical galaxies has shown that the scalar field can couple with ordinary matter with different strengths (different coupling constants), producing and/or depending on the different clustering state of matter components; 3. elliptical and spiral galaxies, combined with clusters of galaxies, show evident correlations among theory parameters, which suggest both the general validity of our results on all scales and a way toward a possible unification of the theory for all types of the gravitational systems we considered. All these results demonstrate that the proposed scalar field scenario can work fairly well as an alternative to dark matter.