On the evolution of environmental and mass properties of strong lens galaxies in COSMOS

Abstract

Context. Nearly 100 new strong-lens candidates have been discovered in the COSMOS field. Among these, 20 lens candidates with 0.34 z lens 1.13 feature multiple images of background sources. Aims. Using the multi-wavelength coverage of the field and its spectroscopic follow-up, we characterize the evolution with redshift of the environment and of the dark-matter (DM) fraction of the lens galaxies. Methods. We present spectroscopic and new photometric redshifts of the strong-lens candidates. The lens environment is characterized in the following way: we account for the projected 10 closest galaxies around each lens and for galaxies with a projected distance less than 1 Mpc at the lens galaxy redshift. In both cases, we perform similar measurements on a control sample of "twin" non-lens early-type galaxies (ETGs). In addition, we identify group members and field galaxies in the X-ray and optical catalogs of galaxy groups and clusters. From those catalogs, we measure the external shear contribution of the groups/clusters surrounding the lens galaxies. The systems are then modeled using a singular isothermal ellipsoid for the lens galaxies plus the external shear produced by the groups/clusters. Results. We observe that the average stellar mass of lens galaxies increases with redshift. In addition, we measure that the environment of lens galaxies is compatible with that of the twins over the whole redshift range tested here. During the lens modeling, we notice that when let free, the external shear points in a direction which is the mean direction of the external shear produced by the groups/clusters and of the closest galaxy to the lens. We also notice that the DM fraction of the lens galaxies measured within the Einstein radius significantly decreases as the redshift increases. Conclusions. Given these observations, we conclude that while the environment of lens galaxies is compatible with that of non-lens ETGS over a wide range of redshifts, their mass properties evolves significantly with redshift: it is still not clear whether this advocates in favor of a stronger lensing bias toward massive objects at high redshift or if it is simply representative of the high proportion of massive and high stellar density galaxies at high redshift.

Galaxy Scale Lenses in the Rcs2. I. First Catalog of Candidate Strong Lenses

“…Previous studies have only shown weak evolution of the dark matter fraction with redshift (Treu & Koopmans 2004;Auger et al 2010;Faure et al 2011;Ruff et al 2011), in agreement (within the errors) with our findings. However, the mass resolution attainable with the current information does not permit significant constraints on the evolution, with no evolution also being consistent within the uncertainties.…”

“…In particular, strong lensing systems in which both lenses and sources are galaxies can provide insights into several current astrophysical and cosmological topics. For example, the configuration of the lensing-induced multiple images and arcs of a background source and their relative fluxes can be used to study the mass profile of lensing galaxies (e.g., Kochanek & Dalal 2004;Gavazzi et al 2007) and their evolution (e.g., Faure et al 2011;Lagattuta et al 2010;Treu et al 2005), including the measure of galactic substructure (e.g., Vegetti & Koopmans 2009;Keeton & Moustakas 2009). On the other hand, the magnification induced by lensing allows for the study of intrinsically faint and distant sources (e.g., Claeskens et al 2006;Anguita et al 2009;Koester et al 2010;Bayliss et al 2010).…”

The Sloan Lens ACS Survey. XIII. Discovery of 40 New Galaxy-scale Strong Lenses∗

“…The comparatively less massive S4TM lens sample serves as a complementary addition to the current galaxy-scale strong-lens samples, which are usually biased toward more massive lens galaxies (e.g., Auger et al 2010;Faure et al 2011;Brownstein et al 2012;Sonnenfeld et al 2013). It extends the lens-galaxy mass coverage to the lower-mass end, and can allow a more thorough investigation of the mass structure and scaling relations of ETGs when combined with other strong-lens samples, especially the SLACS sample which is selected from the same parent sample with the same selection technique.…”

The last 6 Gyr of dark matter assembly in massive galaxies from the Kilo Degree Survey

“…In some cases the datasets are restricted to small samples and small redshift windows to evaluate the dependence of the galaxy DM content on redshift, as in the case of gravitational lenses (Auger et al 2009, 2010, Tortora et al 2010bSonnenfeld et al 2013). The first studies have given contrasting results (Faure et al 2011;Ruff et al 2011). The reason of the tensions among these latter studies probably resides in the paucity of the galaxy samples and differences in the model choices.…”