17454( 2) - 12-Sep-2023 10:23:52 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17454 Version: 2 Check-in Time: 12-Sep-2023 10:23:52 STScI Edit Number: 0 Title A candidate nearly-dark galaxy with 4 globular clusters ------------------------------------------------------------------------------------ Type Cycle GO 31 ------------------------------------------------------------------------------------ Investigators Contact? PI: Prof. Pieter van Dokkum Yale University Y CoI: Mr. Dayi Li University of Toronto N CoI: Dr. William Edgar Harris McMaster University N CoI: Prof. Roberto G. Abraham University of Toronto N CoI: Dr. Shany Danieli Princeton University N CoI: Prof. Gwendolyn Marie Eadie University of Toronto N CoI: Prof. Aaron Romanowsky San Jose State Univ. Research Foundation N ------------------------------------------------------------------------------------ Abstract 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. ------------------------------------------------------------------------------------ Observations Description ------------------------ 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. ------------------------------------------------------------------------------------ 17454( 2) - 12-Sep-2023 10:23:52 - [ 2] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 CDG-1 GALAXY, UNDESIGNATED RA=03H18M12.2500S, J2000 V = 25 DEC=+41D45'53.50" Reference Frame: ICRS Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 17454( 2) - 12-Sep-2023 10:23:52 - [ 3] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-BOX Pattern_Purpose BACKGROUND Number_Of_Points 4 Point_Spacing 13 Line_Spacing 13 Coordinate_Frame POS-TARG Pattern_Orient 23.884 Angle_Between_Sides 81.785 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 17454( 2) - 12-Sep-2023 10:23:52 - [ 4] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 CDG-1 WFC3/UVI ACCUM UVIS2 F200LP 1 1000 S PATTERN 1 1 S see below (5384 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ CDG-1 1 WFC3/UVI ACCUM UVIS2 F200LP 1 none none none 1 1348.0 S S CDG-1 1 WFC3/UVI ACCUM UVIS2 F200LP 2 none none none 1 1348.0 S S CDG-1 1 WFC3/UVI ACCUM UVIS2 F200LP 3 none none none 2 1344.0 S S CDG-1 1 WFC3/UVI ACCUM UVIS2 F200LP 4 none none none 2 1344.0 S S 17454( 2) - 12-Sep-2023 10:23:52 - [ 5] Visit: 02 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 CDG-1 WFC3/UVI ACCUM UVIS2 F200LP 1 1000 S PATTERN 1 1 S see below (5384 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ CDG-1 1 WFC3/UVI ACCUM UVIS2 F200LP 1 none none none 1 1348.0 S S CDG-1 1 WFC3/UVI ACCUM UVIS2 F200LP 2 none none none 1 1348.0 S S CDG-1 1 WFC3/UVI ACCUM UVIS2 F200LP 3 none none none 2 1344.0 S S CDG-1 1 WFC3/UVI ACCUM UVIS2 F200LP 4 none none none 2 1344.0 S S 17454( 2) - 12-Sep-2023 10:23:52 - [ 6] Visit: 03 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 CDG-1 WFC3/UVI ACCUM UVIS2 F200LP 1 1000 S PATTERN 1 1 S see below (5384 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ CDG-1 1 WFC3/UVI ACCUM UVIS2 F200LP 1 none none none 1 1348.0 S S CDG-1 1 WFC3/UVI ACCUM UVIS2 F200LP 2 none none none 1 1348.0 S S CDG-1 1 WFC3/UVI ACCUM UVIS2 F200LP 3 none none none 2 1344.0 S S CDG-1 1 WFC3/UVI ACCUM UVIS2 F200LP 4 none none none 2 1344.0 S S 17454( 2) - 12-Sep-2023 10:23:52 - [ 7] Summary Form for Proposal 17454 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F200LP ------------------------------------------------------------------------------------------------------------------------------------ Target Names CDG-1 ------------------------------------------------------------------------------------------------------------------------------------