(Proposal ID) S17A-155

(PI) Wong, Kenneth

(Proposal Title)
Subaru Adaptive Optics Observations of the Eye of Horus

(Abstract)
Double source plane (DSP) lenses are alignments of a massive lens galaxy with 
two background sources at distinct redshifts. They can provide constraints on 
cosmology and galaxy structure beyond that of typical lenses by breaking 
degeneracies between parameters that vary with source redshift. These systems 
are extremely valuable, but only a handful are known. We have discovered the 
first DSP lens in the HSC survey (the "Eye of Horus") and have 
spectroscopically confirmed both source redshifts.  The brightest image of 
the more distant source (S2) is split into a pair of images by a mass 
component that is undetected in our ground-based data, suggesting the presence 
of a satellite galaxy causing this splitting. In order to better understand 
this system, we need an accurate lens model, accounting for the effects of 
both the main lens galaxy and the intermediate source. Only with high-
resolution imaging can we accurately model this system.  Our proposed AO 
imaging will clearly separate out the two sources, allowing us to use their 
extended surface brightness distributions as lens model constraints. These 
data will also reveal the satellite galaxy responsible for the splitting of 
the brightest image of S2.  With these observations, we can take full 
advantage of the wealth of information from this system.