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

Abstract

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 dark matter. Based on a detection criterion of 10$\ddot{I}ƒ$, we report no significant detection in any of the lenses. Using the sensitivity function at the 10-$\ddot{I}ƒ$ level, we have calculated the predicted number of detectable cold dark matter (CDM) line-of-sight haloes to be $\hat{I}{¼}_l=1.17\pm 1.08$, in agreement with our null detection. Assuming a detection sensitivity that improved to the level implied by a 5-$\ddot{I}ƒ$ threshold, the expected number of detectable line-of-sight haloes rises to $\hat{I}{¼}_l=9.0\pm 3.0$. Whilst the current data find zero detections at this sensitivity level (which has a probability of P${}_{\mathrm{CDM}}^{5\ddot{I}ƒ}(n_{\det }=0)$=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${}_{\mathrm{hm}})<12.26$ at the 2-$\ddot{I}ƒ$ level. The latter is consistent with resonantly produced sterile neutrino masses m${}_{\mathrm{s}}<0.8$ keV at any value of the lepton asymmetry at the 2-$\ddot{I}ƒ$ level.

14 pages, 7 figures, submitted for publication on MNRAS