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Low surface brightness galaxies rotation curves in the low energy limit of R**n gravity: no need for dark matter?
No full text
Dynamical and gravitational lensing properties of a new phenomenological model of elliptical galaxies
No full textAims.Recent observations of the line of sight velocity
profile of elliptical galaxies have furnished controversial
results with some works favouring the presence of a large amount
of dark matter in the outer regions and others arguing in favour
of no dark matter at all. In order to shed new light on this
controversy, we propose here a new phenomenological description of
the total mass profile of galaxies.
Methods.Under the hypothesis of spherical symmetry, we assume a double power-law expression
for the global mass-to-light (hereafter ) ratio
with scaling parameters and determining the inner and outer slope of the ratio. In particular, for
so that mimics a constant ratio in
the inner regions, while, for , thus showing that models with have an asymptotically constant ratio. A wide range of
possibilities is obtained by varying the slope parameters in the range we determine on the basis of
physical considerations. Choosing a general expression for the
luminosity density profile , we work out an effective galaxy model that accounts for all the phenomenology observed in real elliptical galaxies. We derive the
main dynamics and gravitational lensing properties of such an effective model.
Results.We analyze a general class of models, able to
take into account different dynamical trends. We are able to
obtain analytical expressions for the main dynamical and lensing
quantities. We show that constraining the values of makes it possible to analyze the problem of the dark matter
in elliptical galaxies. Indeed, positive values of would be a strong evidence for dark matter.
Conclusions.Finally we indicate possible future approaches in order to face the
observational data, in particular using velocity dispersion
profiles and lensed quasar events
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