0 Assigned ID: 4063 ----- Attempting Submission 1 (Tue May 23 00:33:12 GMT 2023) ----- HST Phase I Proposal 4063 successfully submitted. Receipt: # 4063-1 ----- Attempting Submission 2 (Wed May 24 13:45:08 GMT 2023) ----- 0 ----- Attempting Submission 1 (Mon Sep 11 19:07:45 GMT 2023) ----- A candidate nearly-dark galaxy with 4 globular clusters CDG-1 is a recently-discovered system that may have the most extreme properties yet seen for a low surface brightness dwarf galaxy. An HST imaging survey of the Perseus cluster revealed a tight clump of 4 apparent globular clusters, indicating the presence of a galaxy, but no associated diffuse light. The probability that this grouping occurred by chance is less than 1 in 10^6. CDG-1 may represent the most extreme known case of a galaxy that experienced strong early feedback, driven by the young clusters themselves, that prevented subsequent star formation. In most formation scenarios at least some diffuse star light is expected, and here we propose a sensitive search between the globular clusters using the efficient F200LP filter of UVIS. A detection of diffuse light would demonstrate that CDG-1 is indeed a galaxy, with at least ~95% of its luminosity in the form of globular clusters. The separations between the clusters are only 1-2 arcsec, which makes it impossible to do this program from the ground. The object will be observed with 4 dithered exposures in 2 orbits per visit. Each of the 3 visits is identical, for a total of 6 orbits and 12 exposures. The size of the object is 2''-3'', and the dither box size is 13''. This makes it possible to construct and subtract the local background, while staying far enough away from a very bright star. No post-flash is needed as the F200LP filter provides more than enough counts per exposure. The PI has extensive experience with all aspects of the program, including the reduction and the analysis of HST images. He is an expert on ultra diffuse galaxies and has studied their globular clusters. Dayi Li is the team expert on the statistical methodology for detecting clumps of globular clusters that mark the presence of dwarf galaxies and UDGs in particular. Co-I Dr. Gwendolyn Eadie is a specialist in transferring advanced statistical methods, particularly Bayesian techniques, into astronomical data analysis. Dr. Bob Abraham has extensive experience in imaging techniques for detection of low surface brightness galaxies including UDGs. Dr. William Harris and Dr. Aaron Romanowsky are experts on photometry and spectroscopy of globular cluster populations in galaxies, and in interpreting their application to the early evolution of galaxies. Dr. Shany Danieli is an expert on dwarf galaxy structure and evolution, including ultra diffuse galaxies. 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