JWST lensed quasar dark matter survey - II. Strongest gravitational lensing limit on the dark matter free streaming length to date
Djorgovski, S. G.; Stern, D.; Treu, T.; Moustakas, L. A.; Malkan, M.; Wechsler, R. H.; Bennert, V. N.; Sluse, D.; Anguita, T.; Lemon, C.; Birrer, S.; Motta, V.; Nierenberg, A. M.; Gilman, D.; Abazajian, K. N.; Benson, A. J.; Du, X.; Hoenig, S. F.; Kusenko, A.; Keeley, Ryan E.; Gannon, C.; Gupta, K. K.; Oh, Maverick S. H.
United States, Canada, Chile, Belgium, United Kingdom, Japan, Sweden
Abstract
This is the second in a series of papers in which we use JWST Mid Infrared Instrument multiband imaging to measure the warm dust emission in a sample of 31 multiply imaged quasars, to be used as a probe of the particle nature of dark matter. We present measurements of the relative magnifications of the strongly lensed warm dust emission in a sample of nine systems. The warm dust region is compact and sensitive to perturbations by populations of haloes down to masses $\sim 10^6$ M$_{\odot }$. Using these warm dust flux-ratio measurements in combination with five previous narrow-line flux-ratio measurements, we constrain the halo mass function. In our model, we allow for complex deflector macromodels with flexible third- and fourth-order multipole deviations from ellipticity, and we introduce an improved model of the tidal evolution of subhaloes. We constrain a WDM model and find an upper limit on the half-mode mass of $10^{7.6}\, {\rm M}_\odot$ at posterior odds of 10:1. This corresponds to a lower limit on a thermally produced dark matter particle mass of 6.1 keV. This is the strongest gravitational lensing constraint to date, and comparable to those from independent probes such as the Ly $\alpha$ forest and Milky Way satellite galaxies.