HerMES: The SPIRE confusion limit
  We report on the sensitivity of SPIRE photometers on the Herschel Space
Observatory. Specifically, we measure the confusion noise from observations
taken during the Science Demonstration Phase of the Herschel Multi-tiered
Extragalactic Survey. Confusion noise is defined to be the spatial variation of
the sky intensity in the limit of infinite integration time, and is found to be
consistent among the different fields in our survey at the level of 5.8, 6.3
and 6.8 mJy/beam at 250, 350 and 500 microns, respectively. These results,
together with the measured instrument noise, may be used to estimate the
integration time required for confusion-limited maps, and provide a noise
estimate for maps obtained by SPIRE.
