0 Assigned ID: 1244 ----- Attempting Submission 1 (Wed Sep 30 22:19:41 GMT 2020) ----- HST Phase I Proposal 1244 successfully submitted. Receipt: # 1244-1 ----- Attempting Submission 2 (Wed Sep 30 22:44:43 GMT 2020) ----- Resubmit changing the POS TARG x-value for Visit 01 from blank/NULL to a more explicit "0" value. -1492994660 ----- Attempting Submission 1 (Sun Nov 29 18:20:36 GMT 2020) ----- HST Phase II Proposal 16444 successfully submitted. Receipt: # 16444-1 ----- Attempting Submission 2 (Mon Nov 30 21:42:18 GMT 2020) ----- ----- Attempting Submission 3 (Tue Jan 12 18:39:11 GMT 2021) ----- A bright arc behind an extreme cluster lens at z=1.5 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. 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 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. PI Dahle is an observational astronomer, with a focus on gravitational lensing (both strong and weak). He has been PI for two Cycle 25 HST programmes with multicolor imaging of the brightest rest- UV and Optical gravitationally lensed galaxy (at z=2.37), with results recently presented in Science (Rivera-Thorsen et al. 2019). He has been PI for the ground-based follow-up observations for this target at the 2.56m Nordic Optical Telescope. Co-I Mahler is an expert in strong lensing with ample experience in modeling of galaxy clusters. He is a member of the LENSTOOL development team, and is an expert in MUSE IFU spectroscopy analysis. Co-I Gladders is a observational astronomer, occasional OIR instrument builder, and Professor at the University of Chicago. He specializes in the study of galaxy clusters and strong lenses, mostly at cluster scales, and is the lead- or a co- author of more than 200 refereed publications, mostly on these topics. He is a long term user of HST, with abundant experience in data processing and analysis. Relevant to this proposal, he is the instructing professor for the University of Chicago undergraduate research class that discovered the targeted object. Co-I Rigby is the Operations Project Scientist for JWST, and is the PI of the definitive rest-frame UV spectral atlas Megasaura, and leads a collaboration that is harvesting the spectral diagnostics from this atlas. She is an expert on spectral diagnostics in distant galaxies, and has has been PI of 11 observing programs with Spitzer, Hubble, Chandra, and Herschel, and JWST(ERS). Co-I Sharon is an Associate Professor at the University of Michigan, and is leading the lens modeling analysis of several strong lensing surveys, including the Sloan Giant Arcs Survey (SGAS) and South Pole Telescope (SPT) strong lensing clusters, and is a key participant in treasury HST programs such as the Frontier Fields, BUFFALO, and RELICS. She has ample experience in strong lens modeling and deriving the magnifications and source reconstruction of these sources. Co-I Bayliss is an Assistant Professor at the University of Cincinnati, and an expert on multi-wavelength studies of star formation, gravitational lensing, and galaxy clusters. He has worked with imaging and spectroscopic data from the X-ray to the near infrared, and is an experienced user of Hubble, Chandra, and ground based telescopes. Co-I Florian is an expert in the morphologies, stellar populations, and physical conditions inside distant galaxies, particularly in those that have been gravitationally lensed and has extensive experience working with HST imaging data. Co-I Khullar is a 5th year graduate student at the University of Chicago, working with Co-I Gladders, with expertise in SED modeling, analysis of faint galaxy spectroscopy and HST imaging. He is the TA for the research class that found the proposal target. Co-I Remolina Gonzalez is a postdoctoral researcher in the research group of co-I Sharon at the University of Michigan and has ample experience in lens modeling and analysis of cluster lenses of all scales (including Frontier Fields, Remolina Gonzalez et al. 2018; and SGAS, Sharon et al. 2020), as well as simlated data (Remolina Gonzalez et al. 2020). Co-Is Gozman, Lin, Martinez, Matthews, Medina, Merz, Sanchez, Sisco, Stein, Sukay, and Tavangar are University of Chicago Astronomy and Astrophysics Majors (3rd and 4th year) who discovered COOLJ2129-0126 as part of a current research class with co-I Gladders. Large Scale Structure of the Universe Galaxies 0 false false false false true false false SUPPORTED CLUSTER OF GALAXIES GRAVITATIONAL LENS HIGH REDSHIFT CLUSTER J2000 J2000 g=22.1, r=21.1, z=20.3 ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W WFC3/IR Imaging No No F125W WFC3/IR Imaging No No F160W POS-TARG DITHER 3.034 LINE false false 4 85.29 ACS-WFC-DITHER-LINE 1 false POS-TARG DITHER 0.572 LINE 0.365 false false 74.653 4 18.528 WFC3-IR-DITHER-BOX-MIN 3 false /private/var/folders/py/nv373mr56j15sb4jrbtp880r0000gq/T/OPVisit8499432873669374356.xml The scheduling data was generated by CASM 28.2. CASM was run in Phase II mode. 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CASM was run in Phase II mode. (Tic-Visit :proposal-id 16444 :visit-id "02" :proposal-version -1 :trans-version "20200619" :date "12-Jan-2021 19:23:46.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1810544 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16444 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16444 :visit-id "02" :orbit-number 1 :pcs-time 383 :si-vis-utilization 2700 :al-overhead-at-end 0 :internal-dur-at-end 576 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3142 :pcs-gap 0 ) true 1 0