A High-Significance Measurement of Correlation Between Unresolved IRAS
  Sources and Optically-Selected Galaxy Clusters
  We cross-correlate the 100 um Improved Reprocessing of the IRAS Survey (IRIS)
map and galaxy clusters at 0.1 < z < 0.3 in the maxBCG catalogue taken from the
Sloan Digital Sky Survey, measuring an angular cross-power spectrum over
multipole moments 150 < l < 3000 at a total significance of over 40 sigma. The
cross-spectrum, which arises from the spatial correlation between unresolved
dusty galaxies that make up the cosmic infrared background (CIB) in the IRIS
map and the galaxy clusters, is well-fit by a single power law with an index of
-1.28 +/- 0.12, similar to the clustering of unresolved galaxies from
cross-correlating far-infrared and submillimetre maps at longer wavelengths.
Using a recent, phenomenological model for the spectral and clustering
properties of the IRIS galaxies, we constrain the large-scale bias of the
maxBCG clusters to be 2.6 +/- 1.4, consistent with existing analyses of the
real-space cluster correlation function. The success of our method suggests
that future CIB-optical cross-correlations using Planck and Herschel data will
significantly improve our understanding of the clustering and redshift
distribution of the faint CIB sources.
