Weak lensing signal in unified dark matter models

Abstract

Weak gravitational lensing is a powerful tool for studying both the geometry and the dynamics of the Universe. Its power spectrum contains information on the sources emitting photons and on the large-scale structures that these photons cross. We calculate the weak lensing cosmic convergence and shear power spectra, in linear theory and Limber's approximation, for two different classes of cosmological models: the standard Λ cold dark matter (ΛCDM) and unified dark matter (UDM) models. The latter models attempt to solve the problems of the dark matter in the dynamics of galaxies and galaxy clusters and of the late-time acceleration of the Universe expansion by introducing a scalar field that mimics both dark matter and dark energy. A crucial feature of the UDM models is the speed of sound c∞, i.e. the value of the sound speed at late times, on which structure formation depends. In this paper, we provide the predictions of the UDM models for the weak lensing signal, with various values of c∞. We consider both the cosmic microwave background and background galaxies at different redshifts as sources for the weak lensing power spectra. We find that the power spectra in UDM models are more sensitive to the variations of c∞ for sources located at low redshifts. Moreover, we find that for c∞ > 10−3 (in units of the speed of light), the UDM weak lensing convergence power spectrum Cκκ(l) for background galaxies is strongly suppressed with respect to the ΛCDM spectrum, particularly at small angular scales l≳ 100.