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Arxiv: Discrepancies Between JWST Observations and Simulations of Quenched Massive Galaxies at z > 3: A Comparative Study With IllustrisTNG and ASTRID Published: 6/4/2024 9:00:00 PM Updated: 1/30/2025 3:40:38 PM

Paper abstract: Recent JWST observations have uncovered an unexpectedly large population ofmassive quiescent galaxies at z>3. Using the cosmological simulationsIllustrisTNG and ASTRID, we identify analogous galaxies and investigate theirabundance, formation, quenching mechanisms, and post-quenching evolution forstellar masses 9.5 < \log_{10}{(M_*/{\rm M}_\odot)} < 12. We apply threedifferent quenching definitions and find that both simulations significantlyunderestimate the comoving number density of quenched massive galaxies at z\gtrsim 3 compared to JWST observations by up to ~ 2 dex. In bothsimulations, the high-z quenched massive galaxies often host overmassivecentral black holes above the local M_{BH}-M_* relation, implying thatAGN feedback is key in quenching galaxies in the early Universe. The typicalquenching timescales for these galaxies are ~ 200-600 Myr. IllustrisTNGprimarily employs AGN kinetic feedback, while ASTRID relies on AGN thermalfeedback at z > 2.3, which is less effective and has a longer quenchingtimescale. Although these simulations differ in many aspects, making a directcomparison challenging, our findings suggest the need for improved physicalmodels of AGN feedback in galaxy formation simulations. At lower stellarmasses, the quenched galaxies have denser local environments than thestar-forming galaxies, suggesting that environmental quenching helps quenchless massive galaxies. We also study the post-quenching evolution of thehigh-z massive quiescent galaxies and find that many experience subsequentreactivation of star formation, evolving into primary progenitors of z=0brightest cluster galaxies.