  We describe the survey design and science goals for ODIN (One-hundred-deg^2
DECam Imaging in Narrowbands), a NOIRLab survey using the Dark Energy Camera
(DECam) to obtain deep (AB~25.7) narrow-band images over an unprecedented area
of sky. The three custom-built narrow-band filters, N419, N501, and N673, have
central wavelengths of 419, 501, and 673 nm and respective
full-widthat-half-maxima of 7.2, 7.4, and 9.8 nm, corresponding to Lya at
z=2.4, 3.1, and 4.5 and cosmic times of 2.8, 2.1, and 1.4 Gyr, respectively.
When combined with even deeper, public broad-band data from Hyper Suprime-Cam,
DECam, and in the future, LSST, the ODIN narrow-band images will enable the
selection of over 100,000 Lya-emitting (LAE) galaxies at these epochs.
ODIN-selected LAEs will identify protoclusters as galaxy overdensities, and the
deep narrow-band images enable detection of highly extended Lya blobs (LABs).
Primary science goals include measuring the clustering strength and dark matter
halo connection of LAEs, LABs, and protoclusters, and their respective
relationship to filaments in the cosmic web. The three epochs allow the
redshift evolution of these properties to be determined during the period known
as Cosmic Noon, where star formation was at its peak. The two narrow-band
filter wavelengths are designed to enable interloper rejection and further
scientific studies by revealing [O II] and [O III] at z=0.34, Lya and He II
1640 at z=3.1, and Lyman continuum plus Lya at z=4.5. Ancillary science
includes similar studies of the lower-redshift emission-line galaxy samples and
investigations of nearby star-forming galaxies resolved into numerous [O III]
and [S II] emitting regions.
