2015MNRAS.448.2704I

We investigate the weak lensing effect by line-of-sight structures with a surface mass density of ≲ 10⁸M_☉/arcsec2 in QSO-galaxy quadruple lens systems. Using high-resolution N-body simulations in warm dark matter (WDM) models and observed four quadruple lenses that show anomalies in the flux ratios, we obtain constraints on the mass of thermal WDM, mWDM ≥ 1.3keV (95 percentCL) assuming that the density of the primary lens is described by a singular isothermal ellipsoid (SIE). The obtained constraint is consistent with those from Lyman α forests and the number counts of high-redshift galaxies at z > 4. Our results show that WDM with a free-streaming comoving wavenumber kfs ≤ 27h/Mpc is disfavoured as the major component of cosmological density at redshifts 0.5 ≲ z ≲ 4 provided that the SIE models describe the gravitational potentials of the primary lenses correctly.