0 Assigned ID: 529 ----- Attempting Submission 1 (Fri Apr 05 16:44:48 GMT 2019) ----- 0 ----- Attempting Submission 1 (Wed Jul 17 09:20:33 GMT 2019) ----- Rise of the Titans: Unveiling the Nature of a Binary Hyper-Luminous Starburst at Redshift 6 We propose HST/WFC3-IR and ACS observations in 3 bands to characterize the nature and the environment of ADFS-27, the most distant binary hyper-luminous starburst known, at a redshift of 5.655. This rare, gas-rich (Mgas~2.5x10^11Msun), dusty starburst (SFR~2500Msun/yr) system was recently discovered with ALMA and Herschel. It consists of two merging galaxies ~2kpc in diameter with dynamical masses of >3x10^11Msun each, separated by only 9kpc, resolved in dust emission by ALMA at 0.15" (1kpc) resolution. We here request imaging of the rest-frame ultraviolet light at matching resolution to measure the unobscured star formation rate, stellar mass and star formation history of this system through a complete SED analysis, as well as the morphology and sizes of the stellar disks and the UV extinction profile. We will also use the multi-band data to search for dropout galaxies in its environment on Mpc scales using the Lyman-break technique, which will put constraints on its formation history and the dark matter halo mass scale. This investigation could reveal the presence of a massive proto-cluster of galaxies within the first billion years of the Big Bang. Finally, the HST imaging will unambiguously address the possibility of a weak gravitational magnification of this system. Given its extreme cosmic rarity, this is key to properly place the existence and evolution of ADFS-27 into context with cosmological simulations and models of starburst galaxies at different epochs. This study will be an important pathfinder for detailed investigations of the most exceptional star-forming environments in the early universe with JWST. Program uses 5 orbits, 3 with WFC3/IR in the F098M and F160W filters, and 2 with ACS/WFC and the F606W filter. It is broken up into two visits, one consisting of the two ACS orbits, and the other consisting of the three WFC3 IR orbits (concatenated to ensure similar rotation angles between orbits, and thus, coverage of the same galaxies in both filters - this is not an issue for ACS, given the much larger field of view relative to WFC3, it will cover the full area of interest at any orientation angle). There is no restriction on the orientation angle. All observations are of the same target field (ADFS27). 4-point position/readout dither patterns are employed, primarily to improve the PSF through subpixel sampling, i.e., to mitigate the effects of the large detector pixel sizes (especially for WFC3/IR), as well as to offset by a sufficiently large amount to move persistent pixels to different locations on the sky in each exposure, and to provide good cosmic ray rejection. For ACS/WFC, this is also important to cover the 50 pixel gap in y direction between the two detector chips. The ACS/WFC dither pattern consists of 2 positions with offset large enough to cover the inter-chip gap, and 2 subpositions each to dither on subpixel scales. The WFC3/IR dither patterns consist of 2 postions large enough to cover the "death star" feature, and 2 subpositions each to dither on subpixel scales. For the one F098M orbit, 4 positions are targeted. For the two F160W orbits, each orbit contains two subpixel dither positions, and the larger re-positioning is done between orbits. The PI has published ~200 peer-reviewed publications (h-index 54, approaching 10,000 citations), of which nearly 30 are first author publications. Many of these publications have made use of HST data, and many focus on observations of dusty starburst galaxies (e.g., Riechers et al. 2010, ApJ 720, L131; Riechers et al. 2013, Nature, 496, 329; Riechers et al. 2014, ApJ, 796, 84) and galaxy proto-clusters (e.g., Capak, Riechers et al. 2011, Nature, 470, 233; Pavesi, Riechers et al. 2018, ApJ, 861, 43) and lens modeling (e.g., Riechers et al. 2008, ApJ, 686, 851; Bussmann, Riechers et al. 2015, ApJ, 812, 43) and they include those that invented and establish the techniques used to discover the target of this proposal (e.g., Riechers et al. 2017, ApJ, 850, 1). The entire proposal team has ample experience in these areas, and with HST data analysis, including de-blending, photometry, SED fitting, and Lyman-break selection (see, e.g., Cooray et al. 2014, ApJ, 790, 40 and Laporte et al. 2015, ApJ, 810, 130 for a similar analysis). We have ample computing resources available to analyze the modest amount of data. Galaxies and the IGM 6 false false false false false false false SUPPORTED GALAXY HIGH REDSHIFT GALAXY INTERACTING GALAXY STARBURST ULTRALUMINOUS IR GAL NO ADFS-27 J2000 J2000 ACS/WFC Imaging No No F606W WFC3/IR Imaging No No F098M WFC3/IR Imaging No No F160W POS-TARG DITHER BACKGROUND 2 3.011 LINE false false 0.149 2 85.28 POS-TARG ACS-WFC-DITHER-LINE 34.25 1 true /Users/dr/proposals/HST_2019/OP-cache/adfs27_phase2_v1-v01.xml The scheduling data was generated by CASM 27.2. CASM was run in Phase II mode. 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CASM was run in Phase II mode. 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