Galaxy populations of protoclusters in cosmological hydrodynamical simulations

¹ Department of Physics, University of Trieste, Via G. Tiepolo 11, I-34131 Trieste, Italy
² INAF – Observatory of Trieste, Via G. Tiepolo 11, I-34143 Trieste, Italy
³ IFPU – Institute for Fundamental Physics of the Universe, Via Beirut 2, I-34014 Trieste, Italy
⁴ INFN – Istituto Nazionale di Fisica Nucleare, Via Valerio 2, I-34127 Trieste, Italy
⁵ ICSC – Italian Research Center on High Performance Computing, Big Data and Quantum Computing, Via Magnanelli 2, 40033 Casalecchio di Reno, Italy
⁶ IATE – Instituto de Astronomía Teórica y Experimental, Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina (CONICET), Universidad Nacional de Córdoba, Laprida 854, X5000BGR Córdoba, Argentina

^⋆ Corresponding author: michela.esposito@inaf.it

Received: 18 December 2024
Accepted: 3 March 2025

Abstract

Context. The study of protoclusters at cosmic noon is essential for understanding the impact of the environment and of the transformational processes occurring during this epoch on galaxy properties.

Aims. This work tests the predictions regarding galaxy evolution of the DIANOGA cosmological hydrodynamical simulations of cluster progenitors at z = 2.2 by comparing them with observations and investigates the environmental effects on galaxy populations by comparing simulated protoclusters with an average volume of the Universe.

Methods. We analyzed 14 DIANOGA protoclusters and a cosmological box of 49 cMpc/h per side simulated with OpenGADGET3. We compared predictions and observations of the galaxy stellar mass function (GSMF), the star-forming maif sequence (MS), the fraction of star-forming gas, gas depletion times, and the fraction of quenched galaxies. We also computed the rest-frame UV to near-IR colors of galaxies with the SKIRT-9 radiation transfer code to analyze UVJ diagrams.

Results. We find that the DIANOGA simulations produce a GSMF in broad agreement with observations. The simulated GSMF shows a higher fraction of high-mass galaxies (M_* > 10¹⁰ M_⊙) in massive halos in protoclusters compared to the cosmological box. The same signal, albeit with a lower significance, is also observed in the wide-field protocluster structures, indicating an accelerated evolution of galaxies before their infall into massive halos. Our simulations underestimate star formation rates of galaxies both in protoclusters and in the cosmological box compared to the observed counterparts due to an underestimation of the star-forming gas reservoirs. We find a weak suppression of star formation rates in protocluster galaxies (∼0.05 dex) compared to the cosmological box, which increases up to ∼0.25 dex in massive halos, reflecting suppressed cold gas reservoirs. The quenched galaxy fraction varies significantly across different protocluster halos, which is consistent with observations at z ∼ 2 − 2.5. The simulations showed a strong dependence of quenched fractions on host halo mass as well as an excess of quenched galaxies in the wide-field protocluster region outside the most massive halos in comparison with the cosmological box. Our UVJ diagram analysis showed qualitative agreement with observed color distributions of star-forming and quenched galaxies, except for few massive galaxies in the cores of massive halos where age-dependent extinction results in steeper reddening vectors than typically assumed in observational studies.