Broadband Intensity Mapping of the Ultraviolet-Optical Background with
  CASTOR and SPHEREx
  Broadband tomography statistically extracts the redshift distribution of
frequency dependent emission from the cross correlation of intensity maps with
a reference catalog of galaxy tracers. We make forecasts for the performance of
future all-sky UV experiments doing broadband tomography. We consider the
Cosmological Advanced Survey Telescope for Optical-UV Research (CASTOR) and the
Spectro-Photometer for the History of the Universe, Epoch of Reionization, and
Ices Explorer (SPHEREx). We show that under reasonable error models, CASTOR
measures the UV background SED 2-10 times better than existing data. It will
also expand the applicable redshift range from the current z < 1 to z~0-3 with
CASTOR and z=5-9 with SPHEREx. We show that CASTOR can provide competitive
constraints on the EBL monopole to those available from galaxy number counts
and direct measurement techniques. At high redshift especially, these results
will help understand galaxy formation and reionization. Our modelling code and
chains are publicly available.
