  The Cosmic Dawn Intensity Mapper (CDIM) will transform our understanding of
the era of reionization when the Universe formed the first stars and galaxies,
and UV photons ionized the neutral medium. CDIM goes beyond the capabilities of
upcoming facilities by carrying out wide area spectro-imaging surveys,
providing redshifts of galaxies and quasars during reionization as well as
spectral lines that carry crucial information on their physical properties.
CDIM will make use of unprecedented sensitivity to surface brightness to
measure the intensity fluctuations of reionization on large-scales to provide a
valuable and complementary dataset to 21-cm experiments. The baseline mission
concept is an 83-cm infrared telescope equipped with a focal plane of 24 \times
20482 detectors capable of R = 300 spectro-imaging observations over the
wavelength range of 0.75 to 7.5 {\mu}m using Linear Variable Filters (LVFs).
CDIM provides a large field of view of 7.8 deg2 allowing efficient wide area
surveys, and instead of moving instrumental components, spectroscopic mapping
is obtained through a shift-and-stare strategy through spacecraft operations.
CDIM design and capabilities focus on the needs of detecting faint galaxies and
quasars during reionization and intensity fluctuation measurements of key
spectral lines, including Lyman-{\alpha} and H{\alpha} radiation from the first
stars and galaxies. The design is low risk, carries significant science and
engineering margins, and makes use of technologies with high technical
readiness level for space observations.
