A forward-modelling method to infer the dark matter particle mass from strong gravitational lenses

Abstract

A fundamental prediction of the cold dark matter (CDM) model of structure formation is the existence of a vast population of dark matter haloes extending to subsolar masses. By contrast, other dark matter models, such as a warm thermal relic (WDM), predict a cutoff in the mass function at a mass which, for popular models, lies approximately between 107 and 1010 M⊙. We use mock observations to demonstrate the viability of a forward modelling approach to extract information about low-mass dark haloes lying along the line-of-sight to galaxy-galaxy strong lenses. This can be used to constrain the mass of a thermal relic dark matter particle, mDM. With 50 strong lenses at Hubble Space Telescope resolution and a maximum pixel signal-to-noise ratio of ∼50, the expected median 2σ constraint for a CDM-like model (with a halo mass cutoff at 107 M⊙) is mDM > 4.10 keV (50% chance of constraining mDM to be better than 4.10 keV). If, however, the dark matter is a warm particle of mDM = 2.2 keV, our ‘Approximate Bayesian Computation’ method would result in a median estimate of mDM between 1.43 and 3.21 keV. Our method can be extended to the large samples of strong lenses that will be observed by future telescopes, and could potentially rule out the standard CDM model of cosmogony. To aid future survey design, we quantify how these constraints will depend on data quality (spatial resolution and integration time) as well as on the lensing geometry (source and lens redshifts).

Galaxy–galaxy strong lens perturbations: line-of-sight haloes versus lens subhaloes

“…In the lower panel we plot the change in the total deflection angles when a m 200 = 10 8.67 M NFW halo at z = 0.2 perturbs the lensing due to the main lens (subtracting the total deflection angle with the deflection caused only by the main lens). Because of multiplane lensing effects (Schneider, Ehlers & Falco 1992 ; Fleury, Larena & Uzan 2021 ) the change in the deflection angles are no longer isotropic about the perturber centre (Gilman et al 2019 ;He et al 2022 ). Tracing from the observer backwards, the deflection of light rays by the perturber alters where those rays intersect the main lens plane, which in turn alters the deflection angles those rays receives from the main lens.…”

Astrophysical and Cosmological Probes of Dark Matter

“…Luckily, ongoing and future surveys with instruments such as Euclid, the Vera Rubin, and SKA will increase the number of known gravitational lens systems by several orders of magnitudes [602][603][604]. This data, coupled with follow-up observations with, e.g., the ELT, TMT, and JWST, is projected to deliver tight constraints on the halo and subhalo mass function [595,605].…”

Machine Learning and Cosmology

“…Further work [10][11][12] proposed applying parameter inference and uncertainty quantification methods in order to characterize the properties of lensed sources and lensing galaxies. More recently, with an eye towards the large sample of gravitational lenses that will be imaged by forthcoming cosmological surveys like Euclid and LSST, there has been significant effort towards understanding how to utilize machine learning to optimally exploit this data towards source/lens characterization [13][14][15][16], Hubble constant inference [17], and characterization of dark matter substructure within the lensing galaxies [18][19][20][21][22][23][24][25][26][27][28][29] in a scalable manner.…”