Excess of substructure due to primordial black holes

TL;DR

This study investigates how primordial black holes influence low-mass halo and subhalo abundance, revealing a significant excess of substructure that could help constrain dark matter models through lensing and brightness fluctuation observations.

Contribution

The paper provides the first detailed simulation-based predictions of substructure excess due to primordial black holes, aiding observational constraints on PBH dark matter.

Findings

Significant substructure excess with PBHs compared to $ ext{Lambda}$CDM.

Excess factors up to ~6 for certain PBH mass functions.

Persistence of excess even at sub-percent PBH fractions.

Abstract

This paper explores the impact of primordial black holes (PBHs) on the abundance of low-mass haloes and subhaloes in the dark and low-stellar-mass regime, and examines how these effects can be measured through fluctuations in strong lensing and brightness fluctuations in clusters of galaxies, providing potential ways to constrain the fraction of dark matter in PBHs. Various dark matter candidates leave unique imprints on the low-mass range of the halo mass function, which can be challenging to detect. Among these are hot and warm dark matter models, which predict a reduced abundance of low-mass structures compared to the $\Lambda$CDM model. Models with PBHs also affect this mass range, but in the opposite direction, producing an increase in low-mass objects. By examining lensing perturbations in galaxy clusters, constraints can be placed on the low-mass subhalo abundance and, therefore, on these different dark matter models. We aim to provide predictions useful for this type of perturbation in the PBH case. Additionally, we examine the abundance of haloes and subhaloes in the range where the stellar-to-halo mass relation rises steeply, which could be contrasted with brightness fluctuations in clusters caused by low-luminosity satellites. To do this, we run cosmological simulations using the {\small SWIFT} code, comparing a fiducial model with alternative inflationary models, both with and without PBHs. We find a significant excess of substructure in the presence of PBHs compared to $\Lambda$CDM, without altering the abundance of high-mass haloes at redshift zero. This increase reaches factors of $\sim6$ for extended PBH mass functions with exponential cutoffs at $M_{\rm PBH}=10^2M_\odot$ in the range of parameter space where they could make up all of the dark matter, and persists even for sub-percent PBH fractions with cutoffs at $M_{\rm PBH}=10^4M_\odot$.