Galaxy populations in protoclusters at cosmic noon

¹ Department of Physics and Astronomy, Purdue University, 525 Northwestern Ave., West Lafayette, IN 47907, USA
² Department of Physics, University of California, Santa Barbara, CA 93106-9530, USA
³ Las Cumbres Observatory, 6740 Cortona Dr, Suite 102, Goleta, CA 93117-5575, USA
⁴ Universidad Andres Bello, Facultad de Ciencias Exactas, Departamento de Fisica y Astronomia, Instituto de Astrofisica, Fernandez Concha 700, Las Condes, Santiago RM, Chile
⁵ Instituto de Astronomía Teórica y Experimental (IATE), CONICET-UNC, Laprida 854, X500BGR, Córdoba, Argentina
⁶ Department of Astronomy & Astrophysics, The Pennsylvania State University, University Park, PA 16802, USA
⁷ Institute for Gravitation and the Cosmos, The Pennsylvania State University, University Park, PA 16802, USA
⁸ Physics and Astronomy Department, Rutgers, The State University, Piscataway, NJ 08854, USA
⁹ Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, Daejeon 34055, Korea
¹⁰ Department of Physics and Astronomy, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Korea
¹¹ SNU Astronomy Research Center, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Korea
¹² Korea Institute for Advanced Study, 85 Hoegi-ro, Dongdaemun-gu, Seoul 02455, Korea
¹³ Department of Astronomy, University of Massachusetts, Amherst, MA 01003, USA
¹⁴ Department of Astronomy and Space Science, Chungnam National University, 99 Daehak-ro, Yuseong-gu, Daejeon, 34134, Korea
¹⁵ Space Science Exploration Directorate, Korea AeroSpace Administration (KASA), 537 Haeansaneop-ro, Sanam-myeon, Sacheon-si, Gyeongsangnam-do, Korea
¹⁶ Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA

^⋆ Corresponding authors: moira_andrews@ucsb.edu; maria.artale@unab.cl

Received: 15 October 2024
Accepted: 18 April 2025

Abstract

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-deg² DECam Imaging in Narrowbands) survey, which is mapping large-scale structures at z = 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 at z = 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 Lyα luminosity 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 between z = 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 Lyα luminosity 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.