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Colour matters: the effects of lensing on the positional offsets between optical and submillimetre galaxies in Herschel-ATLAS

Bourne, N.; Maddox, S.J.; Dunne, L.; Dye, S.; Eales, S.; Hoyos, C.; Gonzalez-Nuevo, J.; Smith, D.J.B.; Valiante, E.; de Zotti, G.; Ivison, R.J.; Rowlands, K.


N. Bourne

S.J. Maddox

L. Dunne

Associate Professor

S. Eales

C. Hoyos

J. Gonzalez-Nuevo

D.J.B. Smith

E. Valiante

G. de Zotti

R.J. Ivison

K. Rowlands


We report an unexpected variation in the positional offset distributions between Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS) submillimetre (submm) sources and their optical associations, depending on both 250-μm signal-to-noise ratio and 250/350-μm colour. We show that redder and brighter submm sources have optical associations with a broader distribution of positional offsets than would be expected if these offsets were due to random positional errors in the source extraction. The observation can be explained by two possible effects: either red submm sources trace a more clustered population than blue ones, and their positional errors are increased by confusion, or red submm sources are generally at high redshifts and are frequently associated with low-redshift lensing structures which are identified as false counterparts. We perform various analyses of the data, including the multiplicity of optical associations, the redshift and magnitude distributions in H-ATLAS in comparison to HerMES, and simulations of weak lensing, and we conclude that the effects are most likely to be explained by widespread weak lensing of Herschel-SPIRE sources by foreground structures. This has important consequences for counterpart identification and derived redshift distributions and luminosity functions of submm surveys.


Bourne, N., Maddox, S., Dunne, L., Dye, S., Eales, S., Hoyos, C., …Rowlands, K. (2014). Colour matters: the effects of lensing on the positional offsets between optical and submillimetre galaxies in Herschel-ATLAS. Monthly Notices of the Royal Astronomical Society, 444(2),

Journal Article Type Article
Acceptance Date Aug 5, 2014
Publication Date Sep 4, 2014
Deposit Date Apr 27, 2017
Publicly Available Date Apr 27, 2017
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Oxford University Press
Peer Reviewed Peer Reviewed
Volume 444
Issue 2
Keywords gravitational lensing: weak, galaxies: statistics, submillimetre: galaxies
Public URL
Publisher URL
Additional Information This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.


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