Title: Reducing biases on $H_0$ measurements using strong lensing and galaxy dynamics: results from the EAGLE simulation,
Abstract: Cosmological parameter constraints from observations of time-delay lenses are
becoming increasingly precise. However, there may be significant bias and
scatter in these measurements due to, among other things, the so-called
mass-sheet degeneracy. To estimate these uncertainties, we analyze strong
lenses from the largest EAGLE hydrodynamical simulation. We apply a mass-sheet
transformation to the radial density profiles of lenses, and by selecting
lenses near isothermality, we find that the bias on H0 can be reduced to 5%
with an intrinsic scatter of 10%, confirming previous results performed on a
different simulation data set. We further investigate whether combining lensing
observables with kinematic constraints helps to minimize this bias. We do not
detect any significant dependence of the bias on lens model parameters or
observational properties of the galaxy, but depending on the source--lens
configuration, a bias may still exist. Cross lenses provide an accurate
estimate of the Hubble constant, while fold (double) lenses tend to be biased
low (high). With kinematic constraints, double lenses show bias and intrinsic
scatter of 6% and 10%, respectively, while quad lenses show bias and intrinsic
scatter of 0.5% and 10%, respectively. For lenses with a reduced $\chi^2 > 1$,
a power-law dependence of the $\chi^2$ on the lens environment (number of
nearby galaxies) is seen. Lastly, we model, in greater detail, the cases of two
double lenses that are significantly biased. We are able to remove the bias,
suggesting that the remaining biases could also be reduced by carefully taking
into account additional sources of systematic uncertainty.