paper

Characterizing SL2S galaxy groups using the Einstein radius

arXiv:1409.2900 · doi:10.1051/0004-6361/201423696

Abstract

We analyzed the Einstein radius, $I^¸_{E}$ , in our sample of SL2S galaxy groups, and compared it with $R_{A}$ (the distance from the arcs to the center of the lens), using three different approaches: 1.- the velocity dispersion obtained from weak lensing assuming a Singular Isothermal Sphere profile ( $I^¸_{E, I}$ ), 2.- a strong lensing analytical method ( $I^¸_{E, I I}$ ) combined with a velocity dispersion-concentration relation derived from numerical simulations designed to mimic our group sample, 3.- strong lensing modeling ( $I^¸_{E, I I I}$ ) of eleven groups (with four new models presented in this work) using HST and CFHT images. Finally, $R_{A}$ was analyzed as a function of redshift $z$ to investigate possible correlations with L, N, and the richness-to-luminosity ratio (N/L). We found a correlation between $I^¸_{E}$ and $R_{A}$ , but with large scatter. We estimate $I^¸_{E, I}$ = (2.2 $\pm$ 0.9) + (0.7 $\pm$ 0.2) $R_{A}$ , $I^¸_{E, I I}$ = (0.4 $\pm$ 1.5) + (1.1 $\pm$ 0.4) $R_{A}$ , and $I^¸_{E, I I I}$ = (0.4 $\pm$ 1.5) + (0.9 $\pm$ 0.3) $R_{A}$ for each method respectively. We found a weak evidence of anti-correlation between $R_{A}$ and $z$ , with Log $R_{A}$ = (0.58 $\pm$ 0.06) - (0.04 $\pm$ 0.1) $z$ , suggesting a possible evolution of the Einstein radius with $z$ , as reported previously by other authors. Our results also show that $R_{A}$ is correlated with L and N (more luminous and richer groups have greater $R_{A}$ ), and a possible correlation between $R_{A}$ and the N/L ratio. Our analysis indicates that $R_{A}$ is correlated with $I^¸_{E}$ in our sample, making $R_{A}$ useful to characterize properties like L and N (and possible N/L) in galaxy groups. Additionally, we present evidence suggesting that the Einstein radius evolves with $z$ .

Accepted for publication in Astronomy & Astrophysics. Typos corrected