The amplitude of mass fluctuations and mass density of the Universe constrained by strong gravitational lensing

Abstract

We investigate the linear amplitude of mass fluctuations in the universe, $\sigma_8$, and the present mass density parameter of the Universe, $\Omega_\mathrm{m}$, from the statistical strong gravitational lensing. We use the two populations of lens halos model with fixed cooling mass scale $M_\mathrm{c}=3\times 10^{13}h^{-1}M_{\sun}$ to match the observed lensing probabilities, and leave $\sigma_8$ or $\Omega_\mathrm{m}$ as a free parameter to be constrained by data. Another varying parameter is the equation of state of dark energy $\omega$, and its typical values of -1, -2/3, -1/2 and -1/3 are investigated. We find that $\sigma_8$ is degenerate with $\Omega_\mathrm{m}$ in a way similar to that suggested by present day cluster abundance as well as cosmic shear lensing measurements: $\sigma_8\Omega_\mathrm{m}^{0.6}\approx 0.33$ (Bahcall & Bode\cite{bahcall03a} and references therein). However, both $\sigma_8\leq 0.7$ and $\Omega_\mathrm{m}\leq 0.2$ can be safely ruled out, the best value is when $\sigma_8=1.0$, $\Omega_\mathrm{m}=0.3$ and $\omega=-1$. This result is different from that obtained by Bahcall & Bode (\cite{bahcall03a}), who gives $\sigma_8 =0.98\pm 0.1$ and $\Omega_m =0.17\pm 0.05$. For $\sigma_8=1.0$, higher value of $\Omega_\mathrm{m}=0.35$ requires $\omega=-2/3$ and $\Omega_\mathrm{m}=0.40$ requires $\omega=-1/2$.