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

Wardlow, Julie L. and Cooray, Asantha and De Bernardis, Francesco and Amblard, A. and Arumugam, V. and Aussel, H. and Baker, A. J. and Béthermin, M. and Blundell, R. and Bock, J. and Boselli, A. and Bridge, C. and Buat, V. and Burgarella, D. and Bussmann, R. S. and Cabrera-Lavers, A. and Calanog, J. and Carpenter, J. M. and Casey, C. M. and Castro-Rodríguez, N. and Cava, A. and Chanial, P. and Chapin, E. and Chapman, S. C. and Clements, D. L. and Conley, A. and Cox, P. and Dowell, C. D. and Dye, S. and Eales, S. and Farrah, D. and Ferrero, P. and Franceschini, A. and Frayer, D. T. and Frazer, C. and Fu, Hai and Gavazzi, R. and Glenn, J. and González Solares, E. A. and Griffin, M. and Gurwell, M. A. and Harris, A. I. and Hatziminaoglou, E. and Hopwood, R. and Hyde, A. and Ibar, E. and Ivison, R. J. and Kim, S. and Lagache, G. and Levenson, L. and Marchetti, L. and Marsden, G. and Martinez-Navajas, P. and Negrello, M. and Neri, R. and Nguyen, H. T. and O'Halloran, B. and Oliver, S. J. and Omont, A. and Page, M. J. and Panuzzo, P. and Papageorgiou, A. and Pearson, C. P. and Pérez-Fournon, I. and Pohlen, M. and Riechers, D. and Rigopoulou, D. and Roseboom, I. G. and Rowan-Robinson, M. and Schulz, B. and Scott, D. and Scoville, N. and Seymour, N. and Shupe, D. L. and Smith, A. J. and Streblyanska, A. and Strom, A. and Symeonidis, M. and Trichas, M. and Vaccari, M. and Vieira, J. D. and Viero, M. and Wang, L. and Xu, C. K. and Yan, L. and Zemcov, M. (2013) HerMES: Candidate Gravitationally Lensed Galaxies and Lensing Statistics at Submillimeter Wavelengths. The Astrophysical Journal, 762 (1). p. 59. ISSN 0004-637X

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Abstract

We present a list of 13 candidate gravitationally lensed submillimeter galaxies (SMGs) from 95 deg2 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.