Low-mass halo perturbations in strong gravitational lenses at redshift z ∼ 0.5 are consistent with CDM

We use a sample of 17 strong gravitational lens systems from the BELLS GALLERY survey to quantify the amount of low-mass dark matter haloes within the lensing galaxies and along their lines of sight, and to constrain the properties of darkmatter. Based on a detection criterion of 10 sigma, we report no significant detection in any of the lenses. Using the sensitivity function at the 10 sigma level, we have calculated the predicted number of detectable cold dark matter (CDM) line-of-sight haloes to be mu(l) = 1.17 +/- 1.08, in agreement with our null detection. Assuming a detection sensitivity that improved to the level implied by a 5 sigma threshold, the expected number of detectable line-of-sight haloes rises to mu(l) = 9.0 +/- 3.0. Whilst the current data find zero detections at this sensitivity level (which has a probability of P-CDM(5 sigma) (n(det) = 0) = 0.0001 and would be in strong tension with the CDM framework), we find that such a low-detection threshold leads to many spurious detections and non-detections and therefore the current lack of detections is unreliable and requires data with improved sensitivity. Combining this sample with a subsample of 11 SLACS lenses, we constrain the half-mode mass to be log (M-hm) < 12.26 at the 2 sigma level. The latter is consistent with resonantly produced sterile neutrino masses m(s) < 0.8 keV at any value of the lepton asymmetry at the 2 sigma level.