The Serendipitous Observation of a Gravitationally Lensed Galaxy at z = 0.9057 from the Blanco Cosmology Survey: The Elliot Arc

E. J. Buckley-Geer , H. Lin , E. R. Drabek , S. S. Allam , D. L. Tucker , R. Armstrong , W. A. Barkhouse , E. Bertin (1) , M. Brodwin , S. Desai , J. A. Frieman , S. M. Hansen , F. W. High , J. J. Mohr , Y. -T. Lin , C. -C. Ngeow , A. Rest , R. C. Smith , J. Song , A. Zenteno

1 IAP - Institut d'Astrophysique de Paris

We report on the serendipitous discovery in the Blanco Cosmology Survey (BCS) imaging data of a z = 0.9057 galaxy that is being strongly lensed by a massive galaxy cluster at a redshift of z = 0.3838. The lens (BCS J2352-5452) was discovered while examining i- and z-band images being acquired in 2006 October during a BCS observing run. Follow-up spectroscopic observations with the Gemini Multi-Object Spectrograph instrument on the Gemini-South 8 m telescope confirmed the lensing nature of this system. Using weak-plus-strong lensing, velocity dispersion, cluster richness N ₂₀₀, and fitting to a Navarro-Frenk-White (NFW) cluster mass density profile, we have made three independent estimates of the mass M ₂₀₀ which are all very consistent with each other. The combination of the results from the three methods gives M ₂₀₀ = (5.1 ± 1.3) × 10¹⁴ M _⊙, which is fully consistent with the individual measurements. The final NFW concentration c ₂₀₀ from the combined fit is c ₂₀₀ = 5.4^+1.4 _{- 1.1}. We have compared our measurements of M ₂₀₀ and c ₂₀₀ with predictions for (1) clusters from ΛCDM simulations, (2) lensing-selected clusters from simulations, and (3) a real sample of cluster lenses. We find that we are most compatible with the predictions for ΛCDM simulations for lensing clusters, and we see no evidence based on this one system for an increased concentration compared to ΛCDM. Finally, using the flux measured from the [O II]3727 line we have determined the star formation rate of the source galaxy and find it to be rather modest given the assumed lens magnification.

Mots clés: galaxies: high-redshift; gravitational lensing: strong; gravitational lensing: weak; Astrophysics - Cosmology and Nongalactic Astrophysics

Domaines: Planète et Univers [physics]

E. J. Buckley-Geer, H. Lin, E. R. Drabek, S. S. Allam, D. L. Tucker, et al.. The Serendipitous Observation of a Gravitationally Lensed Galaxy at z = 0.9057 from the Blanco Cosmology Survey: The Elliot Arc. The Astrophysical Journal, 2011, 742, ⟨10.1088/0004-637X/742/1/48⟩. ⟨insu-03645856⟩