Characterizing SL2S galaxy groups using the Einstein radius ^{⋆,⋆⋆,⋆⋆⋆}

¹ Centro de Investigaciones de Astronomía, Apartado Postal 264, 5101-A Mérida, Venezuela
e-mail: verdugo@cida.ve
² Universidad de Valparaíso, Departamento de Física y Astronomía, Avenida Gran Bretaña 1111, Casilla 5030 Valparaíso, Chile
³ Departamento de Física, Universidad de los Andes, Cra. 1 No. 18A-10, Edificio Ip, A. A. 4976 Bogotá, Colombia
⁴ Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile
⁵ Laboratoire d’Astrophysique de Toulouse-Tarbes, Université de Toulouse, CNRS, 57 avenue d’Azereix, 65000 Tarbes, France
⁶ Laboratoire d’Astrophysique de Marseille, Université de Provence, CNRS, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
⁷ Dark Cosmology Center, Niels Bohr Institute, University of Copenhagen, Juliane Marie Vej 30, 2100 Copenhagen, Denmark
⁸ Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), The University of Tokyo, 5-1-5 Kashiwanoha, 277-8583 Kashiwa-shi, Chiba, Japan
⁹ Université de Toulouse, UPS-Observatoire Midi-Pyrénées, IRAP, 31400 Toulouse, France
¹⁰ Herzberg Institute of Astrophysics, National Research Council of Canada, Victoria, BC V9E 2E7, Canada
¹¹ Universidad de Los Andes, Posgrado de Física Fundamental, La Hechicera, 5101 Mérida, Venezuela
¹² Institute Utinam, CNRS UMR6213, Université de Franche-Comté, OSU THETA de Franche-Comté-Bourgogne, 25010 Besançon, France

Received: 22 February 2014
Accepted: 9 September 2014

Abstract

Aims. We aim to study the reliability of R_A (the distance from the arcs to the center of the lens) as a measure of the Einstein radius in galaxy groups. In addition, we want to analyze the possibility of using R_A as a proxy to characterize some properties of galaxy groups, such as luminosity (L) and richness (N).

Methods. We analyzed the Einstein radius, θ_E, in our sample of Strong Lensing Legacy Survey (SL2S) galaxy groups, and compared it with R_A, using three different approaches: 1) the velocity dispersion obtained from weak lensing assuming a singular isothermal sphere profile (θ_E,I); 2) a strong lensing analytical method (θ_E,II) combined with a velocity dispersion-concentration relation derived from numerical simulations designed to mimic our group sample; and 3) strong lensing modeling (θ_E,III) of eleven groups (with four new models presented in this work) using Hubble Space Telescope (HST) and Canada-France-Hawaii Telescope (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).

Results. We found a correlation between θ_E and R_A, but with large scatter. We estimate θ_E,I = (2.2 ± 0.9) + (0.7 ± 0.2)R_A, θ_E,II = (0.4 ± 1.5) + (1.1 ± 0.4)R_A, and θ_E,III = (0.4 ± 1.5) + (0.9 ± 0.3)R_A for each method respectively. We found weak evidence of anti-correlation between R_A and z, with Log R_A = (0.58 ± 0.06) − (0.04 ± 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.

Conclusions. Our analysis indicates that R_A is correlated with θ_E in our sample, making R_A useful for characterizing properties like L and N (and possibly N/L) in galaxy groups. Additionally, we present evidence suggesting that the Einstein radius evolves with z.