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Peer-reviewedCC BY 4.0Monthly Notices of the Royal Astronomical Society

Halo mass functions in mixed cold and fuzzy dark matter models

  • Sarah C Johnston1
  • Simon May2
  • Tibor Dome3
  • Sownak Bose1
  • Alastair Basden1
  • Carlton Baugh1
  • Anastasia Fialkov3,4
  • Alex Tocher3,4
4 affiliations
  1. 1Institute for Computational Cosmology, Department of Physics, Durham University , South Road, Durham DH1 3LE ,
  2. 2Fakultät für Physik, Universität Bielefeld , Universitätsstraße 25, D-33615 Bielefeld ,
  3. 3Institute of Astronomy, University of Cambridge , Madingley Road, Cambridge CB3 0HA ,
  4. 4Kavli Institute for Cosmology , Madingley Road, Cambridge CB3 0HA ,
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Abstract

We investigate the impact of mixed cold and fuzzy dark matter (referred to as MDM) cosmologies on the halo mass function (HMF) using numerical simulations performed with the AxiREPO framework. We consider models in which an ultralight axion-like component with mass m =10−24.5 eV constitutes a fraction f ≤ 0.3 of the total dark matter. To enable consistent halo identification in mixed-species scenarios, we develop a grid-based halo-finding pipeline that combines the particle-based cold dark matter (CDM) and wave-like fuzzy dark matter (FDM) components into a unified density field. We find that FDM traces the large-scale CDM distribution while suppressing small-scale structure through wave interference effects, leading to a reduction in the abundance of low-mass haloes and modifying the HMF in a manner dependent on redshift and FDM fraction. Increasing the FDM fraction produces a systematic downward shift in the HMF and modifies its high-mass slope. Motivated by these trends, we introduce a phenomenological model that maps CDM HMFs to their MDM counterparts using a suppression function with parameters dependent on redshift and FDM fraction. This model reproduces the simulated HMFs within approximately 0.1–0.2 dex across the parameter space explored (1 ≤ z ≤ 4, f ≤ 0.3). Our results provide a computationally efficient method for predicting structure formation in MDM cosmologies without requiring dedicated simulations for each parameter choice, and establish a framework for exploring the impact of MDM on cosmological structure formation.

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Cite

BibTeXRIS
BibTeX
@article{johnston2026halo,
  title = {{Halo mass functions in mixed cold and fuzzy dark matter models}},
  author = {Sarah C Johnston and Simon May and Tibor Dome and Sownak Bose and Alastair Basden and Carlton Baugh and Anastasia Fialkov and Alex Tocher},
  journal = {Monthly Notices of the Royal Astronomical Society},
  year = {2026},
  month = oct,
  doi = {10.1093/mnras/stag1892},
  url = {https://academic.oup.com/mnras/article/doi/10.1093/mnras/stag1892/8869237},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Halo mass functions in mixed cold and fuzzy dark matter models
AU  - Sarah C Johnston
AU  - Simon May
AU  - Tibor Dome
AU  - Sownak Bose
AU  - Alastair Basden
AU  - Carlton Baugh
AU  - Anastasia Fialkov
AU  - Alex Tocher
PY  - 2026
DA  - 2026/10/06
JO  - Monthly Notices of the Royal Astronomical Society
DO  - 10.1093/mnras/stag1892
UR  - https://academic.oup.com/mnras/article/doi/10.1093/mnras/stag1892/8869237
AB  - We investigate the impact of mixed cold and fuzzy dark matter (referred to as MDM) cosmologies on the halo mass function (HMF) using numerical simulations performed with the AxiREPO framework. We consider models in which an ultralight axion-like component with mass m =10^−24.5 eV constitutes a fraction f ≤ 0.3 of the total dark matter. To enable consistent halo identification in mixed-species scenarios, we develop a grid-based halo-finding pipeline that combines the particle-based cold dark matter (CDM) and wave-like fuzzy dark matter (FDM) components into a unified density field. We find that FDM traces the large-scale CDM distribution while suppressing small-scale structure through wave interference effects, leading to a reduction in the abundance of low-mass haloes and modifying the HMF in a manner dependent on redshift and FDM fraction. Increasing the FDM fraction produces a systematic downward shift in the HMF and modifies its high-mass slope. Motivated by these trends, we introduce a phenomenological model that maps CDM HMFs to their MDM counterparts using a suppression function with parameters dependent on redshift and FDM fraction. This model reproduces the simulated HMFs within approximately 0.1–0.2 dex across the parameter space explored (1 ≤ z ≤ 4, f ≤ 0.3). Our results provide a computationally efficient method for predicting structure formation in MDM cosmologies without requiring dedicated simulations for each parameter choice, and establish a framework for exploring the impact of MDM on cosmological structure formation.
SN  - 0035-8711
SN  - 1365-2966
ER  -