Double dark matter vision: twice the number of compact-source lenses
  with narrow-line lensing and the WFC3 grism
  The magnifications of compact-source lenses are extremely sensitive to the
presence of low mass dark matter halos along the entire sight line from the
source to the observer. Traditionally, the study of dark matter structure in
compact-source strong gravitational lenses has been limited to radio-loud
systems, as the radio emission is extended and thus unaffected by microlensing
which can mimic the signal of dark matter structure. An alternate approach is
to measure quasar nuclear-narrow line emission, which is free from microlensing
and present in virtually all quasar lenses. In this paper, we double the number
of systems which can be used for gravitational lensing analyses by presenting
measurements of narrow-line emission from a sample of 8 quadruply imaged quasar
lens systems, WGD J0405-3308, HS 0810+2554, RX J0911+0551, SDSS J1330+1810, PS
J1606-2333, WFI 2026-4536, WFI 2033-4723 and WGD J2038-4008. We describe our
updated grism spectral modelling pipeline, which we use to measure narrow-line
fluxes with uncertainties of 2-10\%, presented here. We fit the lensed image
positions with smooth mass models and demonstrate that these models fail to
produce the observed distribution of image fluxes over the entire sample of
lenses. Furthermore, typical deviations are larger than those expected from
macromodel uncertainties. This discrepancy indicates the presence of
perturbations caused by small-scale dark matter structure. The interpretation
of this result in terms of dark matter models is presented in a companion
paper.
