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Aims.We investigate the physical properties and redshift evolution of simulated galaxies residing in unvirialized cosmic structures (i.e., protoclusters) at cosmic noon, to understand the influence of the environment on galaxy formation. This work is intended to build clear expectations for the ongoing ODIN (One-hundred-deg²DECam Imaging in Narrowbands) survey, which is mapping large-scale structures atz= 2.4,3.1, and 4.5 using Lyα-emitting galaxies (LAEs) as tracers. Methods.From the IllustrisTNG simulations, we define subregions centered on the most massive clusters ranked by total stellar mass atz= 0 and study the properties of galaxies within, including those of LAEs. To model the LAE population, we take a semi-analytical approach that assigns Lyαluminosity and equivalent width based on the UV luminosities to galaxies in a probabilistic manner. We investigate stellar mass, star formation rate (SFR), major merger events, and specific star formation rate of the population of star-forming galaxies and LAEs in the field- and protocluster environment and trace their evolution across cosmic time betweenz= 0−4. Results.We find that the overall shape of the UV luminosity function in simulated protocluster environments is characterized by a substantially shallower faint-end slope and a large excess on the bright end, signaling different formation histories for galaxies therein. The difference is milder for the Lyαluminosity function. While protocluster galaxies follow the same SFR-M_★scaling relation as average field galaxies, a larger fraction appears to have experienced major mergers in the last 200 Myr and as a result shows enhanced star formation at a ≈60% level, leading to a flatter distribution in both SFR and M_★relative to galaxies in the average field. We find that protocluster galaxies, including LAEs, begin to quench much earlier (z∼0.8−1.6) than field galaxies (z∼0.5−0.9); our result is in qualitative agreement with recent observational results and highlights the importance of large-scale environment on the overall formation history of galaxies. 

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.