Jung, Seoyoung LylaRennehan, DouglasSaeedzadeh, VidaBabul, ArifTremmel, MichaelQuinn, Thomas R.Loubser, LoubserO'Sullivan, E.Yi, Sukyoung K.2026-03-062026-03-060035-8711https://hdl.handle.net/1885/733807165Contrary to many stereotypes about massive galaxies, observed brightest group galaxies (BGGs) are diverse in their star formation rates, kinematic properties, and morphologies. Studying how they evolve into and express such diverse characteristics is an important piece of the galaxy formation puzzle. We use a high-resolution cosmological suite of simulations Romulus and compare simulated central galaxies in group-scale haloes at z = 0 to observed BGGs. The comparison encompasses the stellar mass-halo mass relation, various kinematic properties and scaling relations, morphologies, and the star formation rates. Generally, we find that Romulus reproduces the full spectrum of diversity in the properties of the BGGs very well, albeit with a tendency toward lower than the observed fraction of quenched BGGs. We find both early-type S0 and elliptical galaxies as well as late-type disc galaxies; we find Romulus galaxies that are fast-rotators as well as slow-rotators; and we observe galaxies transforming from late-type to early-type following strong dynamical interactions with satellites. We also carry out case studies of selected Romulus galaxies to explore the link between their properties, and the recent evolution of the stellar system as well as the surrounding intragroup/circumgalactic medium. In general, mergers/strong interactions quench star-forming activity and disrupt the stellar disc structure. Sometimes, however, such interactions can also trigger star formation and galaxy rejuvenation. Black hole feedback can also lead to a decline of the star formation rate but by itself, it does not typically lead to complete quenching of the star formation activity in the BGGs.This study was started while SLJ was visiting the Department of Physics and Astronomy at the University of Victoria. SLJ acknowledges support from the Korean National Research Foundation (NRF-2017R1A2A05001116) and the Australian National University Research Scholarship. AB, TQ, and MT were partially supported by NSF award AST-1514868. AB, DR [funding reference number 534263], and VS also acknowledge support from NSERC (Canada) through the Discovery Grant program and DR acknowledges additional support from the Natural Sciences and Engineering Research Council of Canada (NSERC) through a Canada Graduate Scholarship. MT is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-2001810. SIL is supported in part by the National Research Foundation of South Africa (NRF Grant Number: 120850). Any opinion, finding and conclusion or recommendation expressed in this material is that of the author(s) and the NRF does not accept any liability in this regard. EOS acknowledges support from the National Aeronautics and Space Administration (NASA) through XMM-Newton award 80NSSC19K1056. SKY acknowledges support from the Korean National Research Foundation (NRF-2020R1A2C3003769).application/pdfen-AU© 2022 The Author(s)202210.1093/mnras/stac16222023-10-01