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Published June 2011 | Published
Journal Article Open

HerMES: detection of cosmic magnification of submillimetre galaxies using angular cross-correlation


Cosmic magnification is due to the weak gravitational lensing of sources in the distant Universe by foreground large-scale structure leading to coherent changes in the observed number density of the background sources. Depending on the slope of the background source number counts, cosmic magnification causes a correlation between the background and foreground galaxies, which is unexpected in the absence of lensing if the two populations are spatially disjoint. Previous attempts using submillimetre (submm) sources have been hampered by small number statistics. The large number of sources detected in the Herschel Multi-tiered Extra-galactic Survey (HerMES) Lockman-Spitzer Wide-area Infrared Extragalactic (SWIRE) field enables us to carry out the first robust study of the cross-correlation between submm sources and sources at lower redshifts. Using ancillary data, we compile two low-redshift samples from Sloan Digital Sky Survey (SDSS) and SWIRE with 〈z〉∼ 0.2 and 0.4, respectively, and cross-correlate with two submm samples based on flux density and colour criteria, selecting galaxies preferentially at z∼ 2. We detect cross-correlation on angular scales between ∼1 and 50 arcmin and find clear evidence that this is primarily due to cosmic magnification. A small, but non-negligible signal from intrinsic clustering is likely to be present due to the tails of the redshift distribution of the submm sources overlapping with those of the foreground samples.

Additional Information

© 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS. Accepted 2011 January 25. Received 2011 January 24; in original form 2010 August 16. Article first published online: 25 Mar. 2011. Herschel is a European Space Agency (ESA) space observatory with science instruments provided by European-led Principle Investigator consortia and with important participation from NASA. LWis supported by UK's Science and Technology Facilities Council grant ST/F002858/1. LW thanks Antony Lewis for helpful discussions. We thank the GAMA team for providing the redshift distribution of F1. The data presented in this paper will be released through the Herschel database in Marseille HeDaM (hedam.oamp.fr/herMES). 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).

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