HerMES: Candidate Gravitationally Lensed Galaxies and Lensing Statistics at Submillimeter Wavelengths

Creators: Wardlow, Julie L.; Cooray, Asantha; Bock, J.; Bridge, C.; Carpenter, J. M.; Dowell, C. D.; Levenson, L.; Nguyen, H. T.; Riechers, D.; Schulz, B.; Scoville, N.; Shupe, D. L.; Vieira, J. D.; Viero, M.; Xu, C. K.; Yan, L.; Zemcov, M.

Abstract

We present a list of 13 candidate gravitationally lensed submillimeter galaxies (SMGs) from 95 deg^2 of the Herschel Multi-tiered Extragalactic Survey, a surface density of 0.14 ± 0.04 deg^(–2). The selected sources have 500 μm flux densities (S_(500)) greater than 100 mJy. Gravitational lensing is confirmed by follow-up observations in 9 of the 13 systems (70%), and the lensing status of the four remaining sources is undetermined. We also present a supplementary sample of 29 (0.31 ± 0.06 deg^(–2)) gravitationally lensed SMG candidates with S_(500) = 80-100 mJy, which are expected to contain a higher fraction of interlopers than the primary candidates. The number counts of the candidate lensed galaxies are consistent with a simple statistical model of the lensing rate, which uses a foreground matter distribution, the intrinsic SMG number counts, and an assumed SMG redshift distribution. The model predicts that 32%-74% of our S_(500) ≥ 100 mJy candidates are strongly gravitationally lensed (μ ≥ 2), with the brightest sources being the most robust; this is consistent with the observational data. Our statistical model also predicts that, on average, lensed galaxies with S_(500) = 100 mJy are magnified by factors of ~9, with apparently brighter galaxies having progressively higher average magnification, due to the shape of the intrinsic number counts. 65% of the sources are expected to have intrinsic 500 μm flux densities less than 30 mJy. Thus, samples of strongly gravitationally lensed SMGs, such as those presented here, probe below the nominal Herschel detection limit at 500 μm. They are good targets for the detailed study of the physical conditions in distant dusty, star-forming galaxies, due to the lensing magnification, which can lead to spatial resolutions of ~0."01 in the source plane.

Additional Information

© 2013 American Astronomical Society. Received 2012 May 16; accepted 2012 November 9; published 2012 December 14. We thank Elisabetta Valiante for providing the redshift distributions from her model and an anonymous referee for thoughtful feedback. 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); and 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, UKSA (UK); and NASA (USA). This research has made use of data from the HerMES project (http://hermes.sussex.ac.uk/). HerMES is a Herschel Key Programme utilizing Guaranteed Time from the SPIRE instrument team, ESAC scientists, and a mission scientist. HerMES is described in Oliver et al. (2012). The data presented in this paper will be released through the HerMES Database in Marseille, HeDaM (http://hedam.oamp.fr/HerMES/). J.L.W., A.C., F.d.B., C.F., S.K., H.F., and J.C. acknowledge partial support from NSF CAREER AST-0645427 (to A.C. at UCI). S.J.O., L.W., and A.S. acknowledge support from the Science and Technology Facilities Council (grant No.ST/F002858/1 and grant No. ST/I000976/1) at U. of Sussex. A.F., G.M., L.M., and M.V. were supported by the Italian Space Agency (ASI "Herschel Science" Contract I/005/07/0). D.R. acknowledges support from NASA through a Spitzer Space Telescope grant. Support for program numbers GO-12194 and GO-12488 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. 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. The authors recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. The Submillimeter Array is a joint project between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics and is funded by the Smithsonian Institution and the Academia Sinica. Support for CARMA construction was derived from the Gordon and Betty Moore Foundation; the Kenneth T. and Eileen L. Norris Foundation; the James S. McDonnell Foundation; the Associates of the California Institute of Technology; the University of Chicago; the states of California, Illinois, and Maryland; and the National Science Foundation. Ongoing CARMA development and operations are supported by the National Science Foundation under a cooperative agreement and by the CARMA partner universities. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain). 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. Based on observations made with the Gran Telescopio Canarias (GTC), installed in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofsica de Canarias, in the island of La Palma. The GTC observations are part of the International Time Programme 2010–2011 (PI: PerezFournon). Facilities: Herschel (SPIRE),CARMA,GBT(Zpectrometer), VLA, Keck:II (NIRC2), Keck:I (LRIS), SMA, IRAM:Interferometer, IRAM:30m, HST (WFC3), Spitzer (IRAC, MIPS), GTC (OSIRIS).

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