The Planck Early Release Compact Source Catalogue (ERCSC) includes nine lists
of highly reliable sources, individually extracted at each of the nine Planck
frequency channels. To facilitate the study of the Planck sources, especially
their spectral behaviour across the radio/infrared frequencies, we provide a
"bandmerged" catalogue of the ERCSC sources. This catalogue consists of 15191
entries, with 79 sources detected in all nine frequency channels of Planck and
6818 sources detected in only one channel. We describe the bandmerging
algorithm, including the various steps used to disentangle sources in confused
regions. The multi-frequency matching allows us to develop spectral energy
distributions of sources between 30 and 857 GHz, in particular across the 100
GHz band, where the energetically important CO J=1->0 line enters the Planck
bandpass. We find ~3-5sigma evidence for contribution to the 100 GHz intensity
from foreground CO along the line of sight to 147 sources with |b|>30 deg. The
median excess contribution is 4.5+/-0.9 percent of their measured 100 GHz flux
density which cannot be explained by calibration or beam uncertainties. This
translates to 0.5+/-0.1 K km s^{-1} of CO which must be clumped on the scale of
the Planck 100 GHz beam, i.e., ~10 arcmin. If this is due to a population of
low mass (~15 Msun) molecular gas clumps, the total mass in these clumps may be
more than 2000 Msun. Further, high-spatial-resolution, ground-based
observations of the high-latitude sky will help shed light on the origin of
this diffuse, clumpy CO emission.Comment: 15 pages, 15 figures, MNRAS in pres
