Day 1103

Friday.

1605.08341
Observational selection biases in time-delay strong lensing and their impact on cosmography
Collett, Cunnington

Inferring cosmo parameters from time-delay SL requires a significant investment of telescope time; it is therefore tempting to focus on the systems with the brightest sources, the highest image multiplicities and the widest image separations.  Investigate if this selection bias can influence the properties of the lenses studied and the cosmo parameters that are inferred.  Using a population of lenses with ellipsoidal power law density profiles, build a sample of double and quadruple image systems.  Assuming reasonable thresholds on image separation and flux, based on current lens monitoring campaigns, find that the typical density profile slopes of montorable lenses are significantly shallower than they put ensemble.  From a sample of quadruple image lenses, find that this selection function can introduce a 3.5% bias on the inferred time-delay distances if the ensemble of deflector properties is used as a prior for a cosmographical analysis.  This bias remains at the 2.4% level when high resolution imaging of the quasar host is used to precisely infer the density profiles of individual lenses.  Also investigate if the lines-of-sight for monitorable SLs are biased.  After adding external convergence, kappa, and shear to the lens population find that the expectation value for kappa is increased by 0.004 and 0.009 for doubles and quads respectively.  Kappa is degenerate with the value of H0 inferred from time delays; fortunately the shift in kappa only induces 0.9 (0.4) percent bias on H0 for quads (doubles).  Conclude that whilst the properties of typical quasar lenses and their lines-of-sight do deviate from the global population, the total magnitude of this effect is likely a subdominant effect for current analyses, but has the potential to be a major systematic for samples of ~25 or more lenses.


1605.08428
Matter in the beam: weak lensing, substructures and the temperature of dark matter
Mahdi, Elahi, Lewis, Power

Compare WL maps of CDM clusters to those in a WDM model corresponding to a thermally produced 0.5 keV DM particle.  Analysis clearly shows that the WL magnification, convergence and shear distributions can be used to distinguish between CDM and WDM models.  WDM models increase the probability of weak magnifications, with the differences being significant to >5 sigma, while leaving no significant imprint on the shear distribution.  WDM clusters analyses in this work are more homogeneous than CDM ones, and the fractional decrease in the amount of material in haloes is proportional to the average increase in the magnification.  This difference arises from matter that would be bound in compact haloes in CDM being smoothly distributed over much larger volumes at lower densities in WDM.  Moreover, the signature does not solely lie in the probability distribution function but in the full spatial distribution of the convergence field.