15325( 4) - 10-Apr-2018 11:18:52 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15325 Version: 4 Check-in Time: 10-Apr-2018 11:18:52 STScI Edit Number: 1 Title HST Imaging of the Eye of Horus, a Double Source Plane Gravitational Lens ------------------------------------------------------------------------------------ Type Cycle GO 25 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Kenneth Wong National Astronomical Observatory of Japan Y (NAOJ) CoI: Dr. Eiichi Egami University of Arizona N CoI: Dr. Anupreeta More Institute for Physics and Mathematics of N the Universe CoI: Prof. Masamune Oguri Institute for Physics and Mathematics of N the Universe CoI: Dr. Alessandro Sonnenfeld Institute for Physics and Mathematics of N the Universe CoI: Prof. Sherry H. Suyu Max-Planck-Institut fur Astrophysik N CoI: Dr. Masayuki Tanaka National Astronomical Observatory of Japan N (NAOJ) CoI: Mr. James Hung-Hsu Chan National Taiwan University, Dept. of N Physics CoI: Dr. Masafusa Onoue National Astronomical Observatory of Japan N (NAOJ) CoI: Dr. Chien-Hsiu Lee Research Corporation of the University of N Hawaii CoI: Dr. Yuto Ichinohe Tokyo Metropolitan University, Department N of Physics CoI: Mr. Anton Timur Jaelani Tohoku University, Astronomical Institute N ------------------------------------------------------------------------------------ Abstract Double source plane (DSP) gravitational lenses are extremely rare alignments of a massive lens galaxy with two background sources at distinct redshifts. The presence of two source planes provides important constraints on cosmology and galaxy structure beyond that of typical lens systems by breaking degeneracies between parameters that vary with source redshift. While these systems are extremely valuable, only a handful are known. We have discovered the first DSP lens, the "Eye of Horus", in the Hyper Suprime-Cam survey and have confirmed both source redshifts with follow-up spectroscopy, making this the only known DSP lens with both source redshifts measured. Furthermore, the brightest image of the most 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 or line-of-sight galaxy causing this splitting. In order to better understand this system and use it for cosmology and galaxy studies, we must construct an accurate lens model, accounting for the lensing effects of both the main lens galaxy and the intermediate source. Only with deep, high-resolution imaging from HST/ACS can we accurately model this system. Our proposed multiband imaging will clearly separate out the two sources by their distinct colors, allowing us to use their extended surface brightness distributions as constraints on our lens model. These data may also reveal the satellite galaxy responsible for the splitting of the brightest image of S2. With 15325( 4) - 10-Apr-2018 11:18:52 - [ 2] these observations, we will be able to take full advantage of the wealth of information provided by this system. ------------------------------------------------------------------------------------ Observations Description ------------------------ We aim to image the double source plane lens, the "Eye of Horus", using the ACS/WFC. Our goal is to obtain a S/N = 3 per pixel for both S1 (z=1.30) in the F606W filter, as well as S2 (z=1.99) in the F850LP filter. To attain this, we require 2 orbits in F606W and 1 orbit in F850LP. We use the ACS-WFC-DITHER-BOX 4-point dither pattern for our observations to eliminate defects and improve the PSF sampling. The entire target is ~10 arcsec across, which easily fits within the ACS field of view. Our proposed observations consist of a single visit of 3 orbits, using the WFC aperture. Orbit 1: Dither 1 (2 exposures in F606W, 1 exposure in F850LP), Dither 2 (1 exposure in F606W) Orbit 2: Dither 2 (1 exposure in F606W, 1 exposure in F850LP), Dither 3 (2 exposures in F606W) Orbit 3: Dither 3 (1 exposure in F850LP), Dither 4 (2 exposures in F606W, 1 exposure in F850LP) ------------------------------------------------------------------------------------ 15325( 4) - 10-Apr-2018 11:18:52 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 EYEOFHORUS GALAXY, EINSTEIN RING, RA=14H24M49.0000S +/- 1", J2000 V = 20.5 +/- 0.5 GRAVITATIONAL LENS DEC=-00D53'22.00" +/- 1" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 15325( 4) - 10-Apr-2018 11:18:52 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.262 Line_Spacing 0.192 Coordinate_Frame POS-TARG Pattern_Orient 18.39 Angle_Between_Sides 68.14 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 15325( 4) - 10-Apr-2018 11:18:52 - [ 5] Visit: 01 (Visit 1) Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 EYEOFHORUS ACS/WFC ACCUM WFC1 F606W 2 540 S GS ACQ SCENARIO BASE1B3; (4546 S) PATTERN 1 1-2 ------------------------------------------------------------------------------------------------------------------------------------ 2 EYEOFHORUS ACS/WFC ACCUM WFC1 F850LP 1 540 S (2290 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ EYEOFHORUS 1 ACS/WFC ACCUM WFC1 F606W 1 none 1 none 1 N/A EYEOFHORUS 1 ACS/WFC ACCUM WFC1 F606W 1 none 2 none 1 N/A EYEOFHORUS 1 ACS/WFC ACCUM WFC1 F606W 2 none 1 none 1 N/A EYEOFHORUS 1 ACS/WFC ACCUM WFC1 F606W 2 none 2 none 2 588.0 S EYEOFHORUS 1 ACS/WFC ACCUM WFC1 F606W 3 none 1 none 2 588.0 S EYEOFHORUS 1 ACS/WFC ACCUM WFC1 F606W 3 none 2 none 2 588.0 S EYEOFHORUS 1 ACS/WFC ACCUM WFC1 F606W 4 none 1 none 3 581.0 S EYEOFHORUS 1 ACS/WFC ACCUM WFC1 F606W 4 none 2 none 3 581.0 S EYEOFHORUS 2 ACS/WFC ACCUM WFC1 F850LP 1 none none none 1 N/A EYEOFHORUS 2 ACS/WFC ACCUM WFC1 F850LP 2 none none none 2 588.0 S EYEOFHORUS 2 ACS/WFC ACCUM WFC1 F850LP 3 none none none 3 581.0 S EYEOFHORUS 2 ACS/WFC ACCUM WFC1 F850LP 4 none none none 3 581.0 S 15325( 4) - 10-Apr-2018 11:18:52 - [ 6] Summary Form for Proposal 15325 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements GS ACQ SCENARIO BASE1B3, PATTERN 1 1-2 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W, F850LP ------------------------------------------------------------------------------------------------------------------------------------ Target Names EYEOFHORUS ------------------------------------------------------------------------------------------------------------------------------------