0 Assigned ID: 287 ----- Attempting Submission 1 (Thu Apr 07 20:52:13 GMT 2016) ----- HST Phase I Proposal 287 (Phase1HST2016.pdf.apt) successfully submitted. Receipt: # 287-1 ----- Attempting Submission 2 (Fri Apr 08 12:47:45 GMT 2016) ----- Changed POS to cover chipgaps for all orientations, as discussed by email. Regards, Thomas Collett -23396907 ----- Attempting Submission 1 (Wed Jul 20 12:59:35 GMT 2016) ----- HST Phase II Proposal 14630 (collett_14630_phaseII_offset.apt) successfully submitted. Receipt: # 14630-1 ----- Attempting Submission 2 (Thu Jul 21 21:37:25 GMT 2016) ----- ----- Attempting Submission 3 (Thu Sep 29 15:37:56 GMT 2016) ----- A unique probe of the dark matter distribution in a halo at z=1: A strong lens with a bright central image Cosmological dark matter simulations predict that the central regions of halos have 1/r density cusps. Baryonic processes and dark matter microphysics may resculpt these dark matter cusps, but these process are poorly understood and only weakly constrained by observations of a few low redshift halos. We have discovered a strong lensing cluster at redshift 1 that includes a bright central image like no other: the central image is resolved! This makes for a uniquely powerful probe of the central regions of a dark matter halo without the need for additional dynamical constraints. An NFW halo cannot reconstruct the data: modelling of our DECam imaging with a double powerlaw density profile shows that the central slope must be much shallower than 1/r over at least the central 35 kpc. We propose to obtain high resolution imaging of this lens with WFC3. This data will be able to conclusively distinguish between a large core and an even larger shallow cusp. It will be the first such measurement at z = 1 and the most precise measurement of the central DM profile of a cluster ever made. The data will also allow for an investigation of dark matter substructures at z=1. When combined with cosmological hydrodynamical simulations these results will place new constraints on the range of baryonic processes and DM microphysics that can flatten the central density profiles of cluster DM halos over kiloparsec scales. We require high resolution imaging of the target in F475W, F606W, F125W and F140W. The required signal-to-noise is achieved with 3 orbits of 606, 2 orbits of 475 and 1 orbit split between 125 and 140. Since resolution is key to our project, we will use 4 dithers in each band to optimally sample the psf. Our target is ~30 arcseconds in diameter and signal-to-noise across the whole target is important. We therefore centre the target on the center of a single UVIS chip: this avoids the target falling on the chip gap. We centre the IR chip on the center of our target. In order to maximise the field of view around the target, we centre the UVIS exposures on chip 1 for the first visit, and chip 2 for the second visit. We offset the second visit by 2 arcseconds so that the full dataset covers the chip gap. Our proposed observations are therefore: Two visits of 3 orbits. First visit: Apperture = UVIS1, and IR Orbit 1: WFC3-UVIS: Dither 1 (F606 then F475), Dither 2 (F606,F475) Orbit 2: WFC3-UVIS: Dither 3 (F606,F475), Dither 4 (F606,F475) Orbit 3: WFC3-IR: Dither 1 (F125,F140), Dither 2 (F125,F140), Dither 3 (F125,F140), Dither 4 (F125,F140) Second visit (alligned with first visit): Apperture = UVIS2, with a small offset to cover the chip gap. Orbit 1: WFC3-UVIS: Dither 1 (F606), Dither 2 (F606), Dither 3 (F606), Dither 4 (F606) Orbit 2: WFC3-UVIS: Dither 1 (F606,F475), Dither 2 (F606,F475) Orbit 3: WFC3-UVIS: Dither 3 (F606,F475), Dither 4 (F606,F475) Intergalactic Medium and Cosmology 12 false false false false false false SUPPORTED CLUSTER OF GALAXIES EINSTEIN RING GRAVITATIONAL LENS HIGH REDSHIFT CLUSTER J2000 J2000 WFC3/UVIS Imaging No No F475W WFC3/UVIS Imaging No No F606W WFC3/IR Imaging No No F125W WFC3/IR Imaging No No F140W POS-TARG DITHER 0.173 LINE 0.112 false false 81.785 4 23.884 WFC3-UVIS-DITHER-BOX 1 false POS-TARG DITHER 0.572 LINE 0.365 false false 74.653 4 18.528 WFC3-IR-DITHER-BOX-MIN 2 false The scheduling data was generated by CASM 24.2. 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