Environmental dependence in the halo model informed by the FLAMINGO simulations
Abstract
Galaxy-galaxy lensing (GGL) measurements around galaxy samples in different environments provide valuable information about the galaxy-halo connection. In such studies the halo model is commonly used to estimate physical parameters from the lensing signal, but the impact of environment is generally not considered. Our aim is to adapt the halo model to allow a density-split GGL analysis and to understand the environmental dependence of the elements of the model. We use the FLAMINGO suite of cosmological hydrodynamical simulations to construct samples of halos in underdense and overdense regions. Environment density is assigned to halos based on halo counts within an aperture, employing different aperture sizes to probe both local and large scales. We utilize spherical apertures with radii between 1 h−1 Mpc and 10 h−1 Mpc. We find a strong dependence on environment for the halo mass function (HMF) and the halo bias. To account for this, we propose an empirical modification that can be applied to existing HMF prescriptions. We find that after a density split, the halo bias is approximately constant with mass. There is also an environmental dependence for the stellar-to-halo-mass relation (SHMR), the conditional stellar mass function, and the mass-concentration relation, all of which can be addressed with existing models. We evaluate the impact of overlooking environment on halo occupation distribution (HOD) parameter inference, finding that it leads to biased estimations of the SHMR and the satellite fraction. These results emphasize the need to review the assumptions adopted in the halo model when working with samples of galaxies binned by environment, and consequently, by galaxy properties that correlate with environment, such as morphology and color.
Related
- Mass Proxy Quality of Halo Properties in IllustrisTNG and FLAMINGO Simulations: II. Galaxies, Stars, and Black Holes
- The host halo masses of AGNs and quasars at z ∼ 3 − 7 with TNG-Cluster, FLAMINGO and other cosmological galaxy simulations
- The FLAMINGO simulations data release
- Radial dependence of galaxy and halo properties in cosmic voids: SDSS DR7 and the ELUCID constrained simulation
- Foreground dependence of the 20 GeV Galactic halo gamma-ray excess and its proposed connection to the LUX-ZEPLIN event
BibTeX
@misc{girardi2026environmental,
title = {{Environmental dependence in the halo model informed by the FLAMINGO simulations}},
author = {G. Martín Girardi and D. Rana and H. Hoekstra and J. Schaye and M. Schaller},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.23997},
eprint = {2610.23997},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.23997},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Environmental dependence in the halo model informed by the FLAMINGO simulations
AU - G. Martín Girardi
AU - D. Rana
AU - H. Hoekstra
AU - J. Schaye
AU - M. Schaller
PY - 2026
DA - 2026/10/15
PB - arXiv
DO - 10.48550/arxiv.2610.23997
UR - https://arxiv.org/abs/2610.23997
AB - Galaxy-galaxy lensing (GGL) measurements around galaxy samples in different environments provide valuable information about the galaxy-halo connection. In such studies the halo model is commonly used to estimate physical parameters from the lensing signal, but the impact of environment is generally not considered. Our aim is to adapt the halo model to allow a density-split GGL analysis and to understand the environmental dependence of the elements of the model. We use the FLAMINGO suite of cosmological hydrodynamical simulations to construct samples of halos in underdense and overdense regions. Environment density is assigned to halos based on halo counts within an aperture, employing different aperture sizes to probe both local and large scales. We utilize spherical apertures with radii between 1 h^−1 Mpc and 10 h^−1 Mpc. We find a strong dependence on environment for the halo mass function (HMF) and the halo bias. To account for this, we propose an empirical modification that can be applied to existing HMF prescriptions. We find that after a density split, the halo bias is approximately constant with mass. There is also an environmental dependence for the stellar-to-halo-mass relation (SHMR), the conditional stellar mass function, and the mass-concentration relation, all of which can be addressed with existing models. We evaluate the impact of overlooking environment on halo occupation distribution (HOD) parameter inference, finding that it leads to biased estimations of the SHMR and the satellite fraction. These results emphasize the need to review the assumptions adopted in the halo model when working with samples of galaxies binned by environment, and consequently, by galaxy properties that correlate with environment, such as morphology and color.
ER -