Herschel(a similar to...)-ATLAS/GAMA: SDSS cross-correlation induced by weak lensing

We report a highly significant (> 10 sigma) spatial correlation between galaxies with S-350 mu m a parts per thousand yen 30 mJy detected in the equatorial fields of the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) with estimated redshifts a parts per thousand(3) 1.5, and Sloan Digital Sky Survey (SDSS) or Galaxy And Mass Assembly (GAMA) galaxies at 0.2 a parts per thousand currency sign z a parts per thousand currency sign 0.6. The significance of the cross-correlation is much higher than those reported so far for samples with non-overlapping redshift distributions selected in other wavebands. Extensive, realistic simulations of clustered sub-mm galaxies amplified by foreground structures confirm that the cross-correlation can be explained by weak gravitational lensing (mu < 2). The simulations also show that the measured amplitude and range of angular scales of the signal are larger than can be accounted for by galaxy-galaxy weak lensing. However, for scales a parts per thousand(2) 2 arcmin, the signal can be reproduced if SDSS/GAMA galaxies act as signposts of galaxy groups/clusters with halo masses in the range 10(13.2)-10(14.5) M-aS (TM). The signal detected on larger scales appears to reflect the clustering of such haloes.