Limousin, M. and Cabanac, R. and Gavazzi, R. and Kneib, J.-P. and Motta, V. and Richard, J. and Thanjavur, K. and Foex, G. and Pello, R. and Crampton, D. and Faure, C. and Fort, B. and Jullo, E. and Marshall, P. and Mellier, Y. and More, A. and Soucail, G. and Suyu, S. and Swinbank, M. and Sygnet, J.-F. and Tu, H. and Valls-Gabaud, D. and Verdugo, T. and Willis, J. (2009) A new window of exploration in the mass spectrum: strong lensing by galaxy groups in the SL2S. Astronomy and Astrophysics, 502 (2). ISSN 0004-6361 http://resolver.caltech.edu/CaltechAUTHORS:20090825-150308011
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The existence of strong lensing systems with Einstein radii covering the full mass spectrum, from ~1-2" (produced by galaxy scale dark matter haloes) to > 10" (produced by galaxy cluster scale haloes) have long been predicted. Many lenses with Einstein radii around 1-2" and above 10" have been reported but very few in between. In this article, we present a sample of 13 strong lensing systems with Einstein radii in the range 3"-8" (or image separations in the range 6"-16"), i.e. systems produced by galaxy group scale dark matter haloes. This group sample spans a redshift range from 0.3 to 0.8. This opens a new window of exploration in the mass spectrum, around 10^(13)–10^(14) M_☉, a crucial range for understanding the transition between galaxies and galaxy clusters, and a range that have not been extensively probed with lensing techniques. These systems constitute a subsample of the Strong Lensing Legacy Survey (SL2S), which aims to discover strong lensing systems in the Canada France Hawaii Telescope Legacy Survey (CFHTLS). The sample is based on a search over 100 square degrees, implying a number density of ~0.13 groups per square degree. Our analysis is based on multi-colour CFHTLS images complemented with Hubble Space Telescope imaging and ground based spectroscopy. Large scale properties are derived from both the light distribution of elliptical galaxies group members and weak lensing of the faint background galaxy population. On small scales, the strong lensing analysis yields Einstein radii between 2.5" and 8". On larger scales, strong lens centres coincide with peaks of light distribution, suggesting that light traces mass. Most of the luminosity maps have complicated shapes, implying that these intermediate mass structures may be dynamically young. A weak lensing signal is detected for 6 groups and upper limits are provided for 6 others. Fitting the reduced shear with a Singular Isothermal Sphere, we find σ_(SIS) ~500 km s^(-1) with large error bars and an upper limit of ~900 km s^(-1) for the whole sample (except for the highest redshift structure whose velocity dispersion is consistent with that of a galaxy cluster). The mass-to-light ratio for the sample is found to be M/L_i ~ 250 (solar units, corrected for evolution), with an upper limit of 500. This compares with mass-to-light ratios of small groups (with σ_(SIS) ~ 300 km s^(-1)) and galaxy clusters (with σ_(SIS) > 1000 km s^(-1)), thus bridging the gap between these mass scales. The group sample released in this paper will be complemented with other observations, providing a unique sample to study this important intermediate mass range in further detail.
|Additional Information:||© 2009 EDP Sciences. Received 4 December 2008; accepted 25 May 2009. ML acknowledges the Agence Nationale de la Recherche (Project number 06-BLAN-0067) and the Centre National d’ Etudes Spatiales (CNES) for their support. The Dark Cosmology Centre is funded by the Danish National Research Foundation. JR is grateful to Caltech for its support. J.P.K. acknowledges the Centre National de la Recherche Scientifique for its support. Part of this project is done under the support of National Natural Science Foundation of China No. 10878003, 10778752, 973Program No. 2007CB815402, Shanghai Foundation No. 08240514100, 07dz22020, and the Leading Academic Discipline Project of Shanghai Normal University DZL805. M.L. acknowledges Sébastien Bardeau for making its sheartool package available, and Masamune Oguri for providing the data used to generate Fig. 1. V.M. acknowledges partial support from FONDECYT through grant 1071008. We acknowledge the referee for a careful reading of the submitted paper and constructive suggestions. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.|
|Subject Keywords:||gravitational lensing; cosmology: large-scale structure of Universe|
|Official Citation:||A new window of exploration in the mass spectrum: strong lensing by galaxy groups in the SL2S M. Limousin, R. Cabanac, R. Gavazzi, J.-P. Kneib, V. Motta, J. Richard, K. Thanjavur, G. Foex, R. Pello, D. Crampton, C. Faure, B. Fort, E. Jullo, P. Marshall, Y. Mellier, A. More, G. Soucail, S. Suyu, M. Swinbank, J.-F. Sygnet, H. Tu, D. Valls-Gabaud, T. Verdugo and J. Willis A&A 502 (2) 445-456 (2009) DOI: 10.1051/0004-6361/200811473|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||26 Aug 2009 21:03|
|Last Modified:||26 Dec 2012 11:15|
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