Galaxy formation in modified gravity -- II. galaxy halo connection and assembly bias

[2606.12565] Galaxy formation in modified gravity -- II. galaxy halo connection and assembly bias Skip to main content Search Submit Donate Log in Search arXiv Press Enter to search · Advanced search Astrophysics > Cosmology and Nongalactic Astrophysics arXiv:2606.12565 (astro-ph) [Submitted on 10 Jun 2026 ( v1 ), last revised 14 Aug 2026 (this version, v2)] Title: Galaxy formation in modified gravity -- II. galaxy halo connection and assembly bias Authors: Michael Collier , Sownak Bose , Baojiu Li View a PDF of the paper titled Galaxy formation in modified gravity -- II. galaxy halo connection and assembly bias, by Michael Collier and 2 other authors View PDF HTML (experimental) Abstract: Modern surveys such as DESI and \textit{Euclid}, which collect data for hundreds of millions of galaxies to map the large-scale structure (LSS) of the Universe, hold the key to determining the cosmological parameters and testing new physics. This ambition, however, is limited by uncertainties in the galaxy-halo connection: the link between observed galaxies and the underlying, unobservable matter field, by accounting for effects such as galaxy bias and assembly bias (AB). These are particularly poorly-understood for modified gravity (MG) models, which are popular alternatives to the cosmological constant to explain accelerated expansion. We approach this problem using mock emission line galaxy (ELG) and luminous red galaxy (LRG) catalogues in $f(R)$ gravity matching the specifications of ongoing Stage-IV galaxy surveys, generated from state-of-the-art MG hydrodynamical simulations. While the interplay between MG -- especially the chameleon screening mechanism -- and galaxy formation leaves complicated imprints in the galaxy-halo connection, a simple physical picture emerges in which halo and galaxy formation are enhanced for progressively more massive haloes over time. We confirm that the basic galaxy-halo connection model, the halo occupation distribution (HOD), in which galaxy occupation is determined solely by halo mass, underestimates galaxy clustering strength in $\Lambda$CDM by $10$--$20\%$ at $z\lesssim1$ when neglecting AB, and demonstrate that MG introduces further complexity. Extending this model with a suitably-chosen environment density as a secondary HOD variable reduces the AB effect in all models to $2$--$3\%$ for $z\lesssim0.5$. This provides a well-motivated starting point for further works on minimising the impact of AB when testing non-standard cosmological models with LSS. Comments: 21 pages, 10 figures + 1 figures in appendix, Accepted for publication in MNRAS Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO) ; Astrophysics of Galaxies (astro-ph.GA) Cite as: arXiv:2606.12565 [astro-ph.CO] (or arXiv:2606.12565v2 [astro-ph.CO] for this version) https://doi.org/10.48550/arXiv.2606.12565 Focus to learn more arXiv-issued DOI via DataCite Submission history From: Michael Collier [ view email ] [v1] Wed, 10 Jun 2026 18:16:06 UTC (1,675 KB) [v2] Fri, 14 Aug 2026 20:39:55 UTC (1,675 KB) Full-text links: Access Paper: View a PDF of the paper titled Galaxy formation in modified gravity -- II. galaxy halo connection and assembly bias, by Michael Collier and 2 other authors View PDF HTML (experimental) TeX Source view license Current browse context: astro-ph.CO < prev | next > new | recent | 2026-06 Change to browse by: astro-ph astro-ph.GA References & Citations INSPIRE HEP NASA ADS Google Scholar Semantic Scholar export BibTeX citation Loading... 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