The velocity dispersion function of early-type galaxies and its redshift evolution: the newest results from lens redshift test

TL;DR

This study uses gravitational lensing data to analyze the evolution of early-type galaxies' velocity dispersion function up to redshift 1, finding a decline in number density and an increase in velocity dispersion consistent with hierarchical galaxy formation models.

Contribution

It provides the largest lensing-based analysis of the VDF evolution, confirming its consistency with ΛCDM and contrasting with stellar mass-downsizing scenarios.

Findings

Number density of lenses declines by a factor of two at z ~ 1.

Characteristic velocity dispersion increases by 20% at z ~ 1.

Results align with hierarchical galaxy formation models.

Abstract

The redshift distribution of galactic-scale lensing systems provides a laboratory to probe the velocity dispersion function (VDF) of early-type galaxies (ETGs) and measure the evolution of early-type galaxies at redshift z ~ 1. Through the statistical analysis of the currently largest sample of early-type galaxy gravitational lenses, we conclude that the VDF inferred solely from strong lensing systems is well consistent with the measurements of SDSS DR5 data in the local universe. In particular, our results strongly indicate a decline in the number density of lenses by a factor of two and a 20% increase in the characteristic velocity dispersion for the early-type galaxy population at z ~ 1. Such VDF evolution is in perfect agreement with the $\Lambda$CDM paradigm (i.e., the hierarchical build-up of mass structures over cosmic time) and different from "stellar mass-downsizing" evolutions obtained by many galaxy surveys. Meanwhile, we also quantitatively discuss the evolution of the VDF shape in a more complex evolution model, which reveals its strong correlation with that of the number density and velocity dispersion of early-type galaxies. Finally, we evaluate if future missions such as LSST can be sensitive enough to place the most stringent constraints on the redshift evolution of early-type galaxies, based on the redshift distribution of available gravitational lenses.