Limits on the Evolution of Galaxies from the Statistics of Gravitational Lenses

Abstract

We use gravitational lenses from the Cosmic Lens All-Sky Survey to constrain the evolution of galaxies since redshift z ~ 1 in the current Λ cold dark matter cosmology. This constraint is unique as it is based on a mass-selected lens sample of galaxies. Our method of statistical analysis is the same as that done in recent work by K.-H. Chae. We parameterize the early-type number density evolution in the form of (1 + z ) ##IMG## [http://ej.iop.org/images/1538-4357/599/2/L61/img1.gif] {img1.gif} and the velocity dispersion in the form of (1 + z ) ##IMG## [http://ej.iop.org/images/1538-4357/599/2/L61/img2.gif] {img2.gif} . We find that ν n = -0.11 ##IMG## [http://ej.iop.org/images/1538-4357/599/2/L61/img3.gif] {img3.gif} (1 σ) if we assume ν v = 0, implying that the number density of early-type galaxies is within 50%-164% of the present-day value at redshift z = 1. Allowing the velocity dispersion to evolve, we find that ν v = -0.4 ##IMG## [http://ej.iop.org/images/1538-4357/599/2/L61/img4.gif] {img4.gif} (1 σ), indicating that the velocity dispersion must be within 57%-107% of the present-day value at z = 1. These results are consistent with the early formation and passive evolution of early-type galaxies. More stringent limits from lensing can be obtained from future large lens surveys and by using very high redshift quasars ( z ##IMG## [http://ej.iop.org/icons/Entities/gtrsim.gif] {gtrsim} 5) such as those found from the Sloan Digital Sky Survey.