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Abstract To understand the formation and evolution of massive cosmic structures, studying them at high redshift, in the epoch when they formed the majority of their mass, is essential. The One-hundred-deg²DECam Imaging in Narrowbands (ODIN) survey is undertaking the widest-area narrowband program to date, to use Lyα-emitting galaxies (LAEs) to trace the large-scale structure (LSS) of the Universe on the scale of 10–100 cMpc at three cosmic epochs. In this work, we present results atz= 3.1 based on early ODIN data in the COSMOS field. We identify protoclusters and cosmic filaments using multiple methods and discuss their strengths and weaknesses. We then compare our observations against the IllustrisTNG suite of cosmological hydrodynamical simulations. The two are in excellent agreement, identifying a similar number and angular size of structures above a specified density threshold. We successfully recover the simulated protoclusters with log(M_z=0/M_⊙) ≳ 14.4 in ∼60% of the cases. With these objects, we show that the descendant masses of our observed protoclusters can be estimated purely based on our 2D measurements, finding a medianz= 0 mass of ∼10^14.5M_⊙. The lack of information on the radial extent of each protocluster introduces a ∼0.4 dex uncertainty in its descendant mass. Finally, we show that the recovery of the cosmic web in the vicinity of protoclusters is both efficient and accurate. The similarity of our observations and the simulations implies that our structure selection is likewise robust and efficient, demonstrating that LAEs are reliable tracers of the LSS. 

Abstract We test whether Lyα emitters (LAEs) and Lyman-break galaxies (LBGs) can be good tracers of high-zlarge-scale structures, using the Horizon Run 5 cosmological hydrodynamical simulation. We identify LAEs using the Lyαemission line luminosity and its equivalent width, and LBGs using the broadband magnitudes atz∼ 2.4, 3.1, and 4.5. We first compare the spatial distributions of LAEs, LBGs, all galaxies, and dark matter around the filamentary structures defined by dark matter. The comparison shows that both LAEs and LBGs are more concentrated toward the dark matter filaments than dark matter. We also find an empirical fitting formula for the vertical density profile of filaments as a binomial power-law relation of the distance to the filaments. We then compare the spatial distributions of the samples around the filaments defined by themselves. LAEs and LBGs are again more concentrated toward their filaments than dark matter. We also find the overall consistency between filamentary structures defined by LAEs, LBGs, and dark matter, with the median spatial offsets that are smaller than the mean separation of the sample. These results support the idea that the LAEs and LBGs could be good tracers of large-scale structures of dark matter at high redshifts. 

Abstract We describe the survey design and science goals for One-hundred-deg²DECam Imaging in Narrowbands (ODIN), a NOIRLab survey using the Dark Energy Camera (DECam) to obtain deep (AB ∼ 25.7) narrowband images over an unprecedented area of sky. The three custom-built narrowband filters,N419,N501, andN673, have central wavelengths of 419, 501, and 673 nm and respective FWHM of 7.5, 7.6, and 10.0 nm, corresponding to Lyαatz= 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 broadband data from the Hyper Suprime-Cam, DECam, and in the future, the Legacy Survey of Space and Time, the ODIN narrowband images will enable the selection of over 100,000 Lyα-emitting (LAE) galaxies at these epochs. ODIN-selected LAEs will identify protoclusters as galaxy overdensities, and the deep narrowband images enable detection of highly extended Lyαblobs (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 for the redshift evolution of these properties to be determined during the period known as Cosmic Noon, where star formation was at its peak. The narrowband filter wavelengths are designed to enable interloper rejection and further scientific studies by revealing [Oii] and [Oiii] atz= 0.34, Lyαand Heii1640 atz= 3.1, and Lyman continuum plus Lyαatz= 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 [Oiii] and [Sii] emitting regions.