0 Assigned ID: 6704 ----- Attempting Submission 1 (Thu Apr 10 21:04:52 GMT 2025) ----- HST Phase I Proposal 6704 successfully submitted. Receipt: # 6704-1 ----- Attempting Submission 2 (Thu Apr 10 22:49:48 GMT 2025) ----- HST Phase I Proposal 6704 successfully submitted. Receipt: # 6704-2 ----- Attempting Submission 3 (Thu Apr 10 23:09:39 GMT 2025) ----- HST Phase I Proposal 6704 successfully submitted. Receipt: # 6704-3 ----- Attempting Submission 4 (Thu Apr 10 23:46:12 GMT 2025) ----- Exposure times tweaked to ensure ~1 min unused visibility per orbit. 666117601 ----- Attempting Submission 1 (Fri Aug 08 22:41:07 GMT 2025) ----- ----- Attempting Submission 2 (Wed Aug 13 01:12:55 GMT 2025) ----- ----- Attempting Submission 3 (Tue Sep 02 22:18:05 GMT 2025) ----- An Extraordinary Strongly-Lensed Ly-C Leaker at z=4.059 We propose HST imaging observations to measure the ionizing photons leaking from a remarkable z=4.059 strongly lensed galaxy. This galaxy, the highest redshift system yet identified to be spewing ionizing photons into the broader cosmos, and only the third strongly-lensed instance of a Ly-C leaker ever found, offers an opportunity to isolate and study the region(s) within the galaxy that are producing ionizing photons that are escaping. In addition to the direct measurement of the leaking ionizing photons we will also gather multi-band imaging, with both HST and JWST, to measure the continuum spectral energy distribitions of all structures within the galaxy. We also propose for initial exploratory JWST spectroscopy to measure restframes emission lines in the nebular gas. All of this imaging and spectroscopy will inform an analysis of the physical conditions within and properties of the leaking components, which be correlated with the leaking Ly-C photons known to be emerging from this galaxy. This program is for imaging of a high redshift (z=4.06) strongly-lensed Lyman continuum leaker. The imaging from HST will be used for several purposes - including measuring the spatial distribution of the leaking photons and constructing a high fidelity lens model - and consist of imaging in 4 filters. Of the allocated 13 orbits, 7 will be used for imaging in the F438W filter; I have programed this as 2 2-orbit visits and 1 3-orbit visit. These data sample the Ly-C photons. To avoid post-flash losses in SNR, we take full orbit length images in each visit, dithered along a line; we add a small position offset to make sure the field is differently sampled (slightly) even if the visits end up occuring sequentially all at the sample rotation. We realise these offsets by specifying two slightly offset targets at +-2 arcsec. Because the lensing radius is reasonably small (maximally a few tens or arcseconds for all possible secondary image configurations) the whole system and all possible secondary lensd images fit comfortably on a single chip of WFC3, and we place the target accordingly on UVIS1-FIX; this places the target such that it will be well way from chip edges at all possible rotations. There are then 2 orbits each allocated to F547M, F606W and F814W, each programmed as a single 2-orbit visit. For each 2-orbit single filter observation, we observe a 4-point dither using a default WFC3-DITHER-UVIS-BOX pattern across the two orbits, to reject cosmic rays and bad pixels and sample the PSF for drizzling. The F547M images require a very slight postflash (level 2) to ensure that charge traps are well filled. PI Gladders is an expert on galaxy clusters, strong lensing and galaxy evolution, and spectroscopic and imaging data processing, and leads an extensive team of undergraduate students at the University of Chicago who are finding and characterizing rare strongly-lensed sources. That collaboration (COOL-LAMPS; ChicagO Optically-selected Lenses Located at the Margins of Public Surveys) discovered the proposed target and many of the involved undergrduates are listed as CoIs here. He will lead the program with extensive help and support from numerous CoIs. Co-I Bayliss is an expert on spectroscopic diagnostics of star formation, gravitational lensing, and galaxy clusters. Co-I Sharon is an expert on strong lens modeling. Co-I Khullar is an expert on SED modeling using various types of data, including the spectroscopy and imaging proposed here. 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 building morphological models using space-based imaging data. Co-I Rigby is the Senior JWST Project Scientist, and an expert on studying distant star-forming galaxies magnified by gravitational lensing. Co-I H. Dahle is an expert on galaxy clusters and gravitational lensing, as well as studies of strongly lensed quasars and galaxies. Co-I Owens is a student working with Dr. Bayliss who has experience analyzing spectra and imaging of strongly lensed star-forming galaxies. Co-I Rivera-Thorsen is an expert on the interstellar and circumgalactic gas in star-forming galaxies, and Ly-C leakers. Co-I Solhaug is a graduate student at the University of Chicago and an expert on LyC-leaking galaxies and Lyman-alpha radiative transfer, and a member of PI Gladder's research group. Co-I Welch is an expert with space data on strongly lensed galaxies, with a focus on extreme magnification events and faint lines spectroscopic diagnostics. Co-I Hutchison is also an expert with space data on strongly lensed galaxiea and an expert in details of the data reductions necessary to ensure best results. Co-I Kim is an expert in measurement and analysis of UV imaging of Ly-C leakers, including extensive past work on the SunBurst Arc. The remaining Co-Is not detailed here are undergraduate studnets working in the PI's group at Chicago. Galaxies 6 false false false false false false true PRIMARY 7.8 true SUPPORTED GALAXY GRAVITATIONAL LENS HIGH REDSHIFT GALAXY PROTOGALAXY YES J2000 J2000 GALAXY GRAVITATIONAL LENS HIGH REDSHIFT GALAXY PROTOGALAXY YES J2000 J2000 GALAXY GRAVITATIONAL LENS HIGH REDSHIFT GALAXY PROTOGALAXY YES J2000 J2000 WFC3/UVIS Imaging No No F438W WFC3/UVIS Imaging No No F547M WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W POS-TARG DITHER 0.173 LINE 0.112 false false 81.785 4 23.884 WFC3-UVIS-DITHER-BOX 1 false POS-TARG DITHER 0.145 LINE false false 2 46.84 WFC3-UVIS-DITHER-LINE 2 false POS-TARG DITHER 0.135 LINE false false 3 46.84 WFC3-UVIS-DITHER-LINE-3PT 3 false The scheduling data was generated by CASM 33.1. 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