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Abstract The One-hundred-deg²DECam Imaging in Narrowbands (ODIN) survey is carrying out a systematic search for protoclusters during Cosmic Noon, using Lyα-emitting galaxies (LAEs) as tracers. Once completed, ODIN aims to identify hundreds of protoclusters at redshifts of 2.4, 3.1, and 4.5 across seven extragalactic fields, covering a total area of up to 91 deg². In this work, we report the high clustering strength of the ODIN protoclusters, determined via measurements of their cross-correlation with LAEs. Our sample consists of 150 protocluster candidates atz = 2.4 and 3.1, identified in two ODIN fields with a total area of 13.9 deg². Atz = 2.4 and 3.1, the inferred protocluster biases are $6.6_{-1.1}^{+1.3}$and $6.1_{-1.1}^{+1.3}$, corresponding to mean halo masses of $\log 〈M/M_{\odot }〉=13.53_{-0.24}^{+0.21}$and $12.96_{-0.33}^{+0.28}$, respectively. By the present day, these protoclusters are expected to evolve into virialized galaxy clusters with a mean mass of ∼10^14.5M_⊙. By comparing the observed number density of protoclusters to that of halos with the same measured clustering strength, we find that the completeness of our sample is of order unity. Finally, the similar descendant masses derived for our samples atz= 2.4 and 3.1, assuming that the halo number density remains constant, suggest that they represent similar structures observed at different cosmic epochs. As a consequence, any observed differences between the two samples can be understood as redshift evolution. The ODIN protocluster samples will thus provide valuable insights into the cosmic evolution of cluster galaxies. 

Abstract In this work, we test the frequent assumption that Lyα-emitting galaxies (LAEs) are experiencing their first major burst of star formation at the time of observation. To this end, we identify 74 LAEs from the ODIN Survey with rest-UV-through-NIR photometry from UVCANDELS. For each LAE, we perform nonparametric star formation history (SFH) reconstruction using the Dense Basis Gaussian-process-based method of spectral energy distribution fitting. We find that a strong majority (67%) of our LAE SFHs align with the frequently assumed archetype of a first major star formation burst, with at most modest star formation rates (SFRs) in the past. However, the rest of our LAE SFHs have significant amounts of star formation in the past, with 28% exhibiting earlier bursts of star formation, with the ongoing burst having the highest SFR (dominant bursts) and the final 5% having experienced their highest SFR in the past (nondominant bursts). Combining the SFHs indicating first and dominant bursts, ∼95% of LAEs are experiencing their largest burst yet: a formative burst. We also find that the fraction of total stellar mass created in the last 200 Myr is ∼1.3 times higher in LAEs than in mass-matched Lyman break galaxy (LBG) samples, and that a majority of LBGs are experiencing dominant bursts, reaffirming that LAEs differ from other star-forming galaxies. Overall, our results suggest that multiple evolutionary paths can produce galaxies with strong observed Lyαemission. 

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 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.