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

He, Qiuhan and Robertson, Andrew and Nightingale, James and Cole, Shaun and Frenk, Carlos S. and Massey, Richard and Amvrosiadis, Aristeidis and Li, Ran and Cao, Xiaoyue and Etherington, Amy (2022) 'A forward-modelling method to infer the dark matter particle mass from strong gravitational lenses.', Monthly Notices of the Royal Astronomical Society, 511 (2). pp. 3046-3062.


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 1010M⊙⁠. 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 107M⊙⁠) is mDM>4.10keV (50 per cent chance of constraining mDM to be better than 4.10 keV). If, however, the dark matter is a warm particle of mDM=2.2keV⁠, 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).

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Publisher statement:This article has been accepted for publication in Monthly notices of the Royal Astronomical Society. ©: 2022 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:16 January 2022
Date deposited:23 May 2022
Date of first online publication:28 January 2022
Date first made open access:23 May 2022

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