Intensity Mapping in the Presence of Foregrounds and Correlated
  Continuum Emission
  Intensity mapping has attracted significant interest as an approach to
measure the properties of the interstellar medium in typical galaxies at high
redshift. Intensity mapping measures the statistics of surface brightness as a
function of frequency, making it sensitive not only to all line emission of
interest but also radiation from all other sources. Significant effort has gone
into developing approaches that reject foreground contamination. Additionally,
the target galaxies have multiple sources of emission that can complicate the
interpretation of the line brightness. We describe the problem of jointly
estimating correlated continuum emission and cleaning uncorrelated continuum
emission, such as from the Milky Way. We apply these considerations to a
cross-correlation of Planck data with BOSS quasars for a determination of CII
for 2 < z < 3.2. Intensity mapping surveys with few bands have unique
challenges for treating foregrounds and avoiding bias from correlated continuum
emission. We show how a future intensity mapping survey with many bands can
separate line from continuum emission in cross-correlation.
