Cosmic equation of state from strong gravitational lensing systems

Abstract

The accelerating expansion of the Universe is a great challenge for both physics and cosmology. In light of lacking the convincing theoretical explanation, an effective description of this phenomenon in terms of a cosmic equation of state turns out useful.The strength of modern cosmology lies in consistency across independent, often unrelated pieces of evidence. Therefore, every alternative method of restricting the cosmic equation of state is important. Strongly gravitationally lensed quasar-galaxy systems create such a new opportunity by combining stellar kinematics (central velocity dispersion measurements) with lensing geometry (Einstein radius determination from position of images).In this paper we apply such a method to a combined data sets from Sloan Lens ACS and Lens Structure and Dynamics surveys of gravitational lenses. As a result we obtain the cosmic equation of state parameters, which generally agree with results already known in the literature. This demonstrates that the method can be further used on larger samples obtained in the future. Independently noticed systematic deviation between fits done on standard candles and standard rulers is revealed in our findings. We also identify an important selection effect crucial to our method associated with the geometric configuration of the lensing system along the line of sight, which may have consequences for sample construction from the future lensing surveys. © 2010 The Authors. Journal compilation © 2010 RAS.