Strong lensing constraints on the dark matter mass through a forward-modelling procedure
Qiuhan He, 26 May 2020
Introduction
Cold and warm dark matter models predict significantly different numbers of dark matter haloes with masses less than ~ 10\(^{-1}\) Msun, which are mostly too small to have a luminous galaxy living in their centres and thus cannot be directly ‘‘seen’’ in the Universe. To visualize those small haloes, strong gravitational lensing is a powerful tool. Light-rays coming from a far background galaxy will not only be deflected by a massive foreground galaxy, but also be perturbed by small haloes happening to fall on the light paths. By studying tiny footprints from small haloes hidden in strong lensing images, we can infer the mass function of small dark haloes and further put a constraint on the mass of dark matter paticles.
Instead of trying to detect individual dark matter haloes by fitting strong lensing images, our goal is to extract collective information from perturbations on lensing images. To be specific, we try to put constraints on the mass function of small dark matter haloes through the power spectrum of lensing image residuals after a smooth fitting to the macro parts of lensintg systems. Our preliminary results have shown that with a forward-modelling procedure and approximate bayesian inference method, under a parametric setting, we can correctly infer the ‘‘cut-off’’ mass of the dark matter mass function from residual power spectra. Although it is not yet ready for real application, our positive results have shown the potential of this new method. The project is still on going and part of results and details will be put online soon.