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Illustrating galaxy–halo connection in the DESI era with illustrisTNG

Yuan, Sihan; Hadzhiyska, Boryana; Bose, Sownak; Eisenstein, Daniel J

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Sihan Yuan

Boryana Hadzhiyska

Daniel J Eisenstein


We employ the hydrodynamical simulation ILLUSTRISTNG to inform the galaxy–halo connection of the Luminous Red Galaxy (LRG) and Emission Line Galaxy (ELG) samples of the Dark Energy Spectroscopic Instrument (DESI) survey at redshift z ∼ 0.8. Specifically, we model the galaxy colours of ILLUSTRISTNG and apply sliding DESI colour–magnitude cuts, matching the DESI target densities. We study the halo occupation distribution (HOD) model of the selected samples by matching them to their corresponding dark matter haloes in the ILLUSTRISTNG dark matter run. We find the HOD of both the LRG and ELG samples to be consistent with their respective baseline models, but also we find important deviations from common assumptions about the satellite distribution, velocity bias, and galaxy secondary biases. We identify strong evidence for concentration-based and environment-based occupational variance in both samples, an effect known as ‘galaxy assembly bias’. The central and satellite galaxies have distinct dependencies on secondary halo properties, showing that centrals and satellites have distinct evolutionary trajectories and should be modelled separately. These results serve to inform the necessary complexities in modelling galaxy–halo connection for DESI analyses and also prepare for building high-fidelity mock galaxies. Finally, we present a shuffling-based clustering analysis that reveals a 10–15  per cent excess in the LRG clustering of modest statistical significance due to secondary galaxy biases. We also find a similar excess signature for the ELGs, but with much lower statistical significance. When a larger hydrodynamical simulation volume becomes available, we expect our analysis pipeline to pinpoint the exact sources of such excess clustering signatures.


Yuan, S., Hadzhiyska, B., Bose, S., & Eisenstein, D. J. (2022). Illustrating galaxy–halo connection in the DESI era with illustrisTNG. Monthly Notices of the Royal Astronomical Society, 512(4), 5793-5811.

Journal Article Type Article
Acceptance Date Mar 21, 2022
Online Publication Date Mar 24, 2022
Publication Date 2022-06
Deposit Date Jun 20, 2022
Publicly Available Date Jun 20, 2022
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 512
Issue 4
Pages 5793-5811


Published Journal Article (2.5 Mb)

Copyright Statement
This article has been accepted for publication in Monthly notices of the Royal Astronomical Society. ©: 2021 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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