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Published September 10, 2011 | Published
Journal Article Open

Modeling of the HerMES Submillimeter Source Lensed by a Dark Matter Dominated Foreground Group of Galaxies


We present the results of a gravitational lensing analysis of the bright z_s = 2.957 submillimeter galaxy (SMG) HERMES found in the Herschel/SPIRE science demonstration phase data from the Herschel Multi-tiered Extragalactic Survey (HerMES) project. The high-resolution imaging available in optical and near-IR channels, along with CO emission obtained with the Plateau de Bure Interferometer, allows us to precisely estimate the intrinsic source extension and hence estimate the total lensing magnification to be μ = 10.9 ± 0.7. We measure the half-light radius R_(eff) of the source in the rest-frame near-UV and V bands that characterize the unobscured light coming from stars and find R_(eff),* = [2.0 ± 0.1] kpc, in good agreement with recent studies on the SMG population. This lens model is also used to estimate the size of the gas distribution (R_(eff,gas) = [1.1 ± 0.5] kpc) by mapping back in the source plane the CO (J = 5 → 4) transition line emission. The lens modeling yields a relatively large Einstein radius R_(Ein) = 4".10 ± 0".02, corresponding to a deflector velocity dispersion of [483 ± 16] km s^(–1). This shows that HERMES is lensed by a galaxy group-size dark matter halo at redshift z_l ~ 0.6. The projected dark matter contribution largely dominates the mass budget within the Einstein radius with f_(dm)(< R_(Ein)) ~ 80%. This fraction reduces to f_(dm)(< R_(eff,G1) ≃ 4.5 kpc) ~ 47% within the effective radius of the main deflecting galaxy of stellar mass M_(*,G1) = [8.5 ± 1.6] × 10^(11) M_☉. At this smaller scale the dark matter fraction is consistent with results already found for massive lensing ellipticals at z ~ 0.2 from the Sloan Lens ACS Survey.

Additional Information

© 2011 The American Astronomical Society. Received 2011 February 9; accepted 2011 June 7; published 2011 August 18. Some of the data presented herein were obtained at the W. M. Keck Observatory which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. R.G. and A.O. acknowledge support from the Centre National de Etudes Spatiales. S.G.D. and A.A.M. acknowledge partial support from SN grant AST-0909182 and the Ajax Foundation. SPIRE has been developed by a consortium of institutes led by Cardiff University (UK) and including University of Lethbridge (Canada); NAOC (China); CEA, LAM (France); IFSI, University of Padua (Italy); IAC (Spain); Stockholm Observatory (Sweden); Imperial College London, RAL, UCL-MSSL, UKATC, University of Sussex (UK); Caltech, JPL, NHSC, University of Colorado (USA). This development has been supported by national funding agencies: CSA (Canada); NAOC (China); CEA, CNES, CNRS (France); ASI (Italy); MCINN (Spain); SNSB (Sweden); STFC (UK); and NASA (USA). The IRAM Plateau de Bure Interferometer is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).

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