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 structure formation is existence a vast population haloes extending to subsolar masses. By contrast, other models, such as warm thermal relic (WDM), predict cutoff in mass function at which, for popular lies approximately between 107 and $10^{10}\, {\rm M}_\odot$. We use mock observations demonstrate viability forward modelling approach extract information about low-mass lying along line sight galaxy–galaxy strong lenses. This can be used constrain particle, mDM. With 50 lenses Hubble Space Telescope resolution maximum pixel signal-to-noise ratio ?50, expected median 2? constraint CDM-like (with halo $10^{7}\, M}_\odot$) $m_\mathrm{DM} \gt 4.10 \, \mathrm{keV}$ (50 per cent chance constraining mDM better than keV). If, however, particle $m_\mathrm{DM}=2.2 \mathrm{keV}$, our ‘approximate Bayesian computation’ method would result estimate 1.43 3.21 keV. Our extended large samples that will observed by future telescopes could potentially rule out standard CDM cosmogony. To aid survey design, we quantify how these constraints depend on data quality (spatial integration time) well lensing geometry (source lens redshifts).