16444( 3) - 12-Jan-2021 20:20:21 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 16444 Version: 3 Check-in Time: 12-Jan-2021 20:20:21 STScI Edit Number: 0 Title A bright arc behind an extreme cluster lens at z=1.5 ------------------------------------------------------------------------------------ Type Cycle GO 28 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Haakon Dahle University of Oslo Y CoI: Dr. Matthew Bayliss University of Cincinnati Main Campus N CoI: Prof. Keren Sharon University of Michigan N CoI: Prof. Michael D. Gladders University of Chicago N CoI: Juan David Remolina Gonzalez University of Michigan N CoI: Dr. Jane R. Rigby NASA Goddard Space Flight Center N CoI: Mr. Gourav Khullar University of Chicago N CoI: Dr. Guillaume Mahler Durham Univ. N CoI: Dr. Michael Florian University of Arizona N CoI: Mr. Jason Lin University of Chicago N CoI: Ms. Katya Gozman University of Chicago N CoI: Mr. Michael Martinez University of Chicago N CoI: Ms. Liz Medina University of Chicago N CoI: Mr. Jorge Sanchez University of Chicago N CoI: Ms. Emily Sisco University of Chicago N CoI: Mr. Daniel Stein University of Chicago N CoI: Mr. Kiyan Tavangar University of Chicago N CoI: Ms. Melissa Merz University of Chicago N CoI: Mr. Ezra Sukay University of Chicago N ------------------------------------------------------------------------------------ Abstract In August 2020 we obtained spectroscopic confirmation of a gravitationally lensed arc at z=3.29 which is exceptionally bright. At its redshift, or higher, it is the brightest arc known. The galaxy cluster responsible for the lensing is also extraordinary: The cluster redshift is z=1.5 and the arc is seen at a large angular radius of 18", more extreme than any previously known cluster lens at these redshifts. The bright lensed source with a spectroscopically measured redshift provides a unique opportunity to use strong lensing to accurately constrain a cluster mass distribution at an early epoch where such measurements have previously not been possible. Through a modest investment of 3 HST orbits, this programme will both produce significant results on its own and be timely preparation for future observations of an extraordinary lensed source and lensing cluster in the coming JWST era. ------------------------------------------------------------------------------------ Observations Description ------------------------ This program consists of 3 orbits of broad-band imaging. Visit 1: ACS/WFC imaging. This is programmed as a 2-orbit visit, with one orbit in each of the F814W and F606W filters. A total of 4 frames are taken per filter, dithering along a line with a gap-crossing dither step for each 16444( 3) - 12-Jan-2021 20:20:21 - [ 2] additional frame. For both filters, the POS TARG option is used to implement an initial 10" offset. The purpose of this offset is to move the cluster center (which coincides with the provided J2000 target coordinates) somewhat closer to the center of the full WFC field, while still avoiding the part of the chip most affected by CTE effects. This offset is small enough that the bright lensed arc (18" from the cluster center) will still be on the same ACS chip as the cluster center for any ORIENT value. Visit 2: WFC3/IR imaging. This single-orbit visit is dedicated to WFC3-IR imaging in two filters, F125W and F160W, following the strategy of similar observations in program 15101. A total of 8 exposures are made - 4 per filter with small box dithers for PSF reconstruction. The pointing is centered on the cluster center. Possible impact of potential reduced gyro operations: We do not require a specific roll angle for these observations. Also, the roll angles for the two separate visits need not be the same. This should maximise the schedulability of the observations, even for the case where the observing windows could become limited by reduced gyro mode. The impact of a reduced gyro mode on limiting the spatial scan speed should also not have a significant impact on our fixed target observations. ------------------------------------------------------------------------------------ 16444( 3) - 12-Jan-2021 20:20:21 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 J2129-0126 CLUSTER OF GALAXIES, RA=21H29M9.0400S, J2000 V = 21.1 g=22.1, r=21.1, z=20.3 GRAVITATIONAL LENS, DEC=-01D26'32.10" HIGH REDSHIFT CLUSTER Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 16444( 3) - 12-Jan-2021 20:20:21 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-LINE Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 3.034 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 85.29 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 3 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-IR-DITHER-BOX-MIN Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.572 Line_Spacing 0.365 Coordinate_Frame POS-TARG Pattern_Orient 18.528 Angle_Between_Sides 74.653 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 16444( 3) - 12-Jan-2021 20:20:21 - [ 5] Visit: 01 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 J2129-0126 ACS/WFC ACCUM WFC1-FIX F606W 1 513 S POS TARG 0, -10; PATTERN see below 1 1 (2052 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 J2129-0126 ACS/WFC ACCUM WFC1-FIX F814W 1 513 S POS TARG 0, -10; PATTERN see below 1 2 (2068 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 | ------------------------------------------------------------------------------------------------------------------------------------ J2129-0126 1 ACS/WFC ACCUM WFC1-FIX F606W 1 none none none 1 513 S J2129-0126 1 ACS/WFC ACCUM WFC1-FIX F606W 2 none none none 1 513 S J2129-0126 1 ACS/WFC ACCUM WFC1-FIX F606W 3 none none none 1 513 S J2129-0126 1 ACS/WFC ACCUM WFC1-FIX F606W 4 none none none 1 513 S J2129-0126 2 ACS/WFC ACCUM WFC1-FIX F814W 1 none none none 2 517.0 S J2129-0126 2 ACS/WFC ACCUM WFC1-FIX F814W 2 none none none 2 517.0 S J2129-0126 2 ACS/WFC ACCUM WFC1-FIX F814W 3 none none none 2 517.0 S J2129-0126 2 ACS/WFC ACCUM WFC1-FIX F814W 4 none none none 2 517.0 S 16444( 3) - 12-Jan-2021 20:20:21 - [ 6] Visit: 02 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 J2129-0126 WFC3/IR MULTIAC IR-FIX F125W NSAMP=12, SAMP-SEQ=SPARS25 1 DEF POS TARG 0, 0; PATTERN 3 CUM (1111.752 1 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 J2129-0126 WFC3/IR MULTIAC IR-FIX F160W NSAMP=12, SAMP-SEQ=SPARS25 1 DEF POS TARG 0, 0; PATTERN 3 CUM (1111.752 2 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 | ------------------------------------------------------------------------------------------------------------------------------------ J2129-0126 1 WFC3/IR MULTIAC IR-FIX F125W 1 none none none 1 N/A CUM J2129-0126 1 WFC3/IR MULTIAC IR-FIX F125W 2 none none none 1 N/A CUM J2129-0126 1 WFC3/IR MULTIAC IR-FIX F125W 3 none none none 1 N/A CUM J2129-0126 1 WFC3/IR MULTIAC IR-FIX F125W 4 none none none 1 N/A CUM J2129-0126 2 WFC3/IR MULTIAC IR-FIX F160W 1 none none none 1 N/A CUM J2129-0126 2 WFC3/IR MULTIAC IR-FIX F160W 2 none none none 1 N/A CUM J2129-0126 2 WFC3/IR MULTIAC IR-FIX F160W 3 none none none 1 N/A CUM J2129-0126 2 WFC3/IR MULTIAC IR-FIX F160W 4 none none none 1 N/A CUM 16444( 3) - 12-Jan-2021 20:20:21 - [ 7] Summary Form for Proposal 16444 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures IR-FIX, WFC1-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC, WFC3/IR ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters NSAMP=12, SAMP-SEQ=SPARS25 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 1, PATTERN 1 2, PATTERN 3 1, PATTERN 3 2, POS TARG 0, -10, POS TARG 0, 0 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F125W, F160W, F606W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names J2129-0126 ------------------------------------------------------------------------------------------------------------------------------------