We analyse the spatial distribution and colour of the intracluster light
(ICL) in 683 clusters of galaxies between z=0.2 and 0.3, selected from approx
1500 deg^2 of the SDSS-DR1. Surface photometry in the g, r and i bands is
conducted on stacked images of the clusters, after rescaling them to the same
metric size and masking out resolved sources. We are able to trace the average
surface brightness profile of the ICL out to 700 kpc, where it is less than
1/10,000 of the mean surface brightness of the dark night sky. The ICL appears
as a clear surface brightness excess with respect to an inner R^1/4 profile
which characterises the mean profile of the BCG. The surface brightness (SB) of
the ICL ranges from 27.5 mag/arcsec^2 at 100 kpc to roughly 32 at 700 kpc in
the observed r-band (26.5 to 31 in the rest-frame g-band). We find that, on
average, the ICL contributes only a small fraction of the total optical
emission in a cluster (10.9+-5.0% within 500 kpc). The radial distribution of
the ICL is more centrally concentrated than that of the cluster galaxies, but
the colours of the two components are identical within the statistical
uncertainties. In the mean the ICL is aligned with and more flattened than the
BCG itself. This alignment is substantially stronger than that of the cluster
light as a whole. The SB of the ICL correlates both with BCG luminosity and
with cluster richness, while the fraction of the total light in the ICL is
almost independent of these quantities. These results support the idea that the
ICL is produced by stripping and disruption of galaxies as they pass through
the central regions of clusters. Our measurements of the diffuse light also
constrain the faint-end slope of the cluster LF. Slopes alpha<-1.35 would imply
more light from undetected galaxies than is observed in the diffuse component.Comment: 21 pages, 12 figures. Accepted for publication in MNRAS. Figures 3
and 4 degraded. Full resolution paper available at
http://www.mpa-garching.mpg.de/~zibetti/ICL_paper.ps.g