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The MillenniumTNG Project: refining the one-halo model of red and blue galaxies at different redshifts

Hadzhiyska, Boryana; Hernquist, Lars; Eisenstein, Daniel; Delgado, Ana Maria; Bose, Sownak; Kannan, Rahul; Pakmor, Rüdiger; Springel, Volker; Contreras, Sergio; Barrera, Monica; Ferlito, Fulvio; Hernández-Aguayo, César; White, Simon D M; Frenk, Carlos

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Boryana Hadzhiyska

Lars Hernquist

Daniel Eisenstein

Ana Maria Delgado

Rahul Kannan

Rüdiger Pakmor

Volker Springel

Sergio Contreras

Monica Barrera

Fulvio Ferlito

César Hernández-Aguayo

Simon D M White


Luminous red galaxies (LRGs) and blue star-forming emission-line galaxies (ELGs) are key tracers of large-scale structure used by cosmological surveys. Theoretical predictions for such data are often done via simplistic models for the galaxy–halo connection. In this work, we use the large, high-fidelity hydrodynamical simulation of the MillenniumTNG project (MTNG) to inform a new phenomenological approach for obtaining an accurate and flexible galaxy-halo model on small scales. Our aim is to study LRGs and ELGs at two distinct epochs, z = 1 and z = 0, and recover their clustering down to very small scales,
r ∼ 0.1 h−1 Mpc, i.e. the one-halo regime, while a companion paper extends this to a two-halo model for larger distances. The occupation statistics of ELGs in MTNG inform us that (1) the satellite occupations exhibit a slightly super-Poisson distribution, contrary to commonly made assumptions, and (2) that haloes containing at least one ELG satellite are twice as likely to host a central ELG. We propose simple recipes for modelling these effects, each of which calls for the addition of a single free parameter to simpler halo occupation models. To construct a reliable satellite population model, we explore the LRG and ELG satellite radial and velocity distributions and compare them with those of subhaloes and particles in the simulation. We find that ELGs are anisotropically distributed within haloes, which together with our occupation results provides strong evidence for cooperative galaxy formation (manifesting itself as one-halo galaxy conformity); i.e. galaxies with similar properties form in close proximity to each other. Our refined galaxy-halo model represents a useful improvement of commonly used analysis tools and thus can be of help to increase the constraining power of large-scale structure surveys.


Hadzhiyska, B., Hernquist, L., Eisenstein, D., Delgado, A. M., Bose, S., Kannan, R., …Frenk, C. (2023). The MillenniumTNG Project: refining the one-halo model of red and blue galaxies at different redshifts. Monthly Notices of the Royal Astronomical Society, 524(2), 2524–2538.

Journal Article Type Article
Acceptance Date Jan 19, 2023
Online Publication Date Jul 20, 2023
Publication Date 2023-09
Deposit Date Feb 1, 2024
Publicly Available Date Feb 1, 2024
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 524
Issue 2
Pages 2524–2538
Public URL


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