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Centro de Astrofísica da Universidade do Porto

Constraints on the dark matter sound speed from galactic scales: The cases of the modified and extended Chaplygin gas

P. P. Avelino, V. M. C. Ferreira

Abstract
We show that the observed rotation curves of spiral galaxies constrain the sound speed of the dark matter to be cs<10−4c , where c is the speed of light in vacuum. Using the modified Chaplygin gas as a representative example of a class of unified dark energy models incorporating an effective dark matter component with a nonzero sound speed, we determine the most stringent constraint to date on the value of the constant contribution to the equation of state parameter in this class of models. Finally, we explain the reason why previous constraints using the cosmic microwave background and baryonic acoustic oscillations were not as competitive as the one presented in this paper and discuss the limitations of the recently proposed extended Chaplygin gas.

Keywords
Dark matter, Dark energy, Galactic halos, Cosmology

Physical Review D
Volume 91, Page 083508
April 2015

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