17787( 3) - 17-Oct-2024 15:02:46 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17787 Version: 3 Check-in Time: 17-Oct-2024 15:02:46 STScI Edit Number: 0 Title DELVE 1: The Least Massive Galaxy? ------------------------------------------------------------------------------------ Type Cycle GO 32 ------------------------------------------------------------------------------------ Investigators Contact? PI: William Cerny Yale University Y CoI: Dr. Joshua D. Simon Carnegie Institution of Washington N CoI: Prof. Marla C. Geha Yale University N CoI: Dr. Alexander Pung Ji University of Chicago N CoI: Dr. Andrew Pace Carnegie Mellon University N CoI: Dr. Ting Li University of Toronto N CoI: Prof. Eric F. Bell University of Michigan N CoI: Dr. Burcin Mutlu-Pakdil Dartmouth College N CoI: Dr. Holger Baumgardt University of Queensland N ------------------------------------------------------------------------------------ Abstract The Milky Way satellite DELVE 1 may be the faintest, smallest, and least-massive galaxy known. However, the alternative possibility that DELVE 1 is a chemically-peculiar, very metal poor star cluster has thus far proven impossible to rule out through spectroscopy; this is because the system has too few bright stars to enable definitive velocity or metallicity dispersion measurements capable of distinguishing between these scenarios. Classifying the system as a dwarf galaxy or star cluster will therefore require an independent avenue that does not rely on ground-based spectroscopy. Here, we request 12 orbits of HST/ACS F606W+F814W imaging to construct a deep color--magnitude diagram of DELVE 1 and test whether the system displays stellar mass segregation. The presence of mass segregation would imply short dynamical times in DELVE 1 consistent with a star cluster, while its absence would provide strong evidence that DELVE 1 is a dark matter dominated dwarf galaxy. Our proposed observations will either confirm DELVE 1 as the least-massive galaxy yet discovered or would suggest that DELVE 1 is the first known example of a uniformly carbon-enhanced star cluster formed directly out of gas enriched by Population III supernovae. Whatever the outcome, these results will have important implications for the nature of dark matter and the formation of the lowest mass galaxies and most metal-poor star clusters. ------------------------------------------------------------------------------------ Observations Description ------------------------ This 12-orbit, 6-visit program images the DELVE 1 stellar system with ACS in the F606W and F814W filters, with WFC3 UVIS coordinated parallels in the same filters. Three pointings (labeled NORTH, SOUTHEAST, SOUTHWEST) have been placed to cover the system contiguously out to at roughly twice its half-light radius for any possible ORIENT. Each of the three pointings is split into 2 visits at the SAME ORIENT: one visit consisting of two orbits of F606W imaging and the other visit consists of one orbit of F814W imaging and one orbit split between F606W and F814W. In other words, 3 pointings x 2 visits/pointing x 2 orbits/visit = 12 prime orbits. For each filter and pointing, we use a 17787( 3) - 17-Oct-2024 15:02:46 - [ 2] ACS-WFC-DITHER-LINE pattern to cover the chip gap. In practice, we use a 4-point LINE for the F606W exposures and a 3-point LINE for the F814W exposures. The single fifth exposure in F606W from the split F606W+F814W orbit is not part of this pattern and is placed at the center of each of the three main pointings. These LINE patterns favor filling the chip gaps and providing CR removal over perfect subpixel sampling. Lastly, we note that there are two bright (G ~ 12) stars covered by our fields. These two stars will certainly saturate but we expect this will not be a major issue (based on similar ACS observations in the archive). However, "glint" artifacts may also occur; the SAME ORIENT restriction will help ensure that any possible glints are localized to the same region of the detector within a given pointing, allowing them to be masked at the analysis stage. ------------------------------------------------------------------------------------ 17787( 3) - 17-Oct-2024 15:02:46 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 DELVE1-SOUTH STELLAR CLUSTER, RA=16H30M58.0230S, J2000 V = 16 EAST GLOBULAR CLUSTER DEC=-00D58'56.95" Reference Frame: ICRS Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 0.0 0.0 0.0 0 ------------------------------------------------------------------------------------------------------------------------------------ 2 DELVE1-NORTH STELLAR CLUSTER, RA=16H30M53.7378S, J2000 V = 16 GLOBULAR CLUSTER DEC=-00D57'17.98" Reference Frame: ICRS Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 0.0 0.0 0.0 0 ------------------------------------------------------------------------------------------------------------------------------------ 3 DELVE1-SOUTH STELLAR CLUSTER, RA=16H30M49.7445S, J2000 V = 16 WEST GLOBULAR CLUSTER DEC=-00D58'52.38" Reference Frame: ICRS Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 0.0 0.0 0.0 0 ------------------------------------------------------------------------------------------------------------------------------------ 17787( 3) - 17-Oct-2024 15:02:46 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-LINE Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 3.034 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 85.29 Angle_Between_Sides Center_Pattern YES ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-LINE Pattern_Purpose DITHER Number_Of_Points 3 Point_Spacing 3.034 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 85.29 Angle_Between_Sides Center_Pattern YES ------------------------------------------------------------------------------------------------------------------------------------ 17787( 3) - 17-Oct-2024 15:02:46 - [ 5] Visit: 01 (N_606_Visit) Visit Requirements: On Hold Comments: Additional Comments: 2 orbits of F606W imaging on the northern pointing; 4 point DITHER-LINE Cpar with F606W imaging 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 DELVE1-NORT ACS/WFC ACCUM WFC F606W 1 1100 S PATTERN 1 1-2; PAR 2 H see below WITH 1 (4542 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS F606W 1 1100 S S see below (4654 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 | ------------------------------------------------------------------------------------------------------------------------------------ DELVE1-NORTH 1 ACS/WFC ACCUM WFC F606W 1 none none none 1 1121.0 S DELVE1-NORTH 1 ACS/WFC ACCUM WFC F606W 2 none none none 1 1121.0 S DELVE1-NORTH 1 ACS/WFC ACCUM WFC F606W 3 none none none 2 1150.0 S DELVE1-NORTH 1 ACS/WFC ACCUM WFC F606W 4 none none none 2 1150.0 S ANY 2 WFC3/UVI ACCUM UVIS F606W 1 none none none 1 1173.0 S S ANY 2 WFC3/UVI ACCUM UVIS F606W 2 none none none 1 1123.0 S S ANY 2 WFC3/UVI ACCUM UVIS F606W 3 none none none 2 1184.0 S S ANY 2 WFC3/UVI ACCUM UVIS F606W 4 none none none 2 1174.0 S S 17787( 3) - 17-Oct-2024 15:02:46 - [ 6] Visit: 02 (SE_606_Visit) Visit Requirements: On Hold Comments: Additional Comments: 2 orbits of F606W imaging on the southeastern pointing; 4 point DITHER-LINE Cpar with F606W imaging 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 DELVE1-SOUT ACS/WFC ACCUM WFC F606W 1 1100 S PATTERN 1 1-2; PAR 2 HEAST see below WITH 1 (4542 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS F606W 1 1100 S S see below (4654 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 | ------------------------------------------------------------------------------------------------------------------------------------ DELVE1-SOUTHEAST 1 ACS/WFC ACCUM WFC F606W 1 none none none 1 1121.0 S DELVE1-SOUTHEAST 1 ACS/WFC ACCUM WFC F606W 2 none none none 1 1121.0 S DELVE1-SOUTHEAST 1 ACS/WFC ACCUM WFC F606W 3 none none none 2 1150.0 S DELVE1-SOUTHEAST 1 ACS/WFC ACCUM WFC F606W 4 none none none 2 1150.0 S ANY 2 WFC3/UVI ACCUM UVIS F606W 1 none none none 1 1173.0 S S ANY 2 WFC3/UVI ACCUM UVIS F606W 2 none none none 1 1123.0 S S ANY 2 WFC3/UVI ACCUM UVIS F606W 3 none none none 2 1184.0 S S ANY 2 WFC3/UVI ACCUM UVIS F606W 4 none none none 2 1174.0 S S 17787( 3) - 17-Oct-2024 15:02:46 - [ 7] Visit: 03 (SW_606_Visit) Visit Requirements: On Hold Comments: Additional Comments: 2 orbits of F606W imaging on the southwestern pointing; 4 point DITHER-LINE Cpar with F606W imaging 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 DELVE1-SOUT ACS/WFC ACCUM WFC F606W 1 1100 S PATTERN 1 1-2; PAR 2 HWEST see below WITH 1 (4542 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS F606W 1 1100 S S see below (4654 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 | ------------------------------------------------------------------------------------------------------------------------------------ DELVE1-SOUTHWEST 1 ACS/WFC ACCUM WFC F606W 1 none none none 1 1121.0 S DELVE1-SOUTHWEST 1 ACS/WFC ACCUM WFC F606W 2 none none none 1 1121.0 S DELVE1-SOUTHWEST 1 ACS/WFC ACCUM WFC F606W 3 none none none 2 1150.0 S DELVE1-SOUTHWEST 1 ACS/WFC ACCUM WFC F606W 4 none none none 2 1150.0 S ANY 2 WFC3/UVI ACCUM UVIS F606W 1 none none none 1 1173.0 S S ANY 2 WFC3/UVI ACCUM UVIS F606W 2 none none none 1 1123.0 S S ANY 2 WFC3/UVI ACCUM UVIS F606W 3 none none none 2 1184.0 S S ANY 2 WFC3/UVI ACCUM UVIS F606W 4 none none none 2 1174.0 S S 17787( 3) - 17-Oct-2024 15:02:46 - [ 8] Visit: 04 (N_606814_Visit) Visit Requirements: SAME ORIENT AS 01 On Hold Comments: Additional Comments: Northern pointing; one orbit of entirely F814W imaging with UVIS F814 cpar; one orbit of F606W +F814W with UVIS cpar on both filters 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 DELVE1-NORT ACS/WFC ACCUM WFC F814W 1 1181 S PATTERN 2 1-2; PAR 2 H see below WITH 1 (3806 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS F814W 1 1181 S S (4002 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 DELVE1-NORT ACS/WFC ACCUM WFC F606W 1 570 S PAR 4 WITH 3 H see below (681 S) Comments: Single 606 exposure to complement the other four from the first visit ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFC3/UVI ACCUM UVIS F606W 1 688 S S see below (723 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 | ------------------------------------------------------------------------------------------------------------------------------------ DELVE1-NORTH 1 ACS/WFC ACCUM WFC F814W 1 none none none 1 1121.0 S DELVE1-NORTH 1 ACS/WFC ACCUM WFC F814W 2 none none none 1 1121.0 S DELVE1-NORTH 1 ACS/WFC ACCUM WFC F814W 3 none none none 2 1564.0 S ANY 2 WFC3/UVI ACCUM UVIS F814W 1 none none none 1 N/A S ANY 2 WFC3/UVI ACCUM UVIS F814W 2 none none none 1 1247.0 S S ANY 2 WFC3/UVI ACCUM UVIS F814W 3 none none none 2 1574.0 S S DELVE1-NORTH 3 ACS/WFC ACCUM WFC F606W none none none none 2 681.0 S ANY 4 WFC3/UVI ACCUM UVIS F606W none none none none 2 723.0 S S 17787( 3) - 17-Oct-2024 15:02:46 - [ 9] Visit: 05 (SE_606814_Visit) Visit Requirements: SAME ORIENT AS 02 On Hold Comments: Additional Comments: Southeastern pointing; one orbit of entirely F814W imaging with UVIS F814 cpar; one orbit of F606W +F814W with UVIS cpar on both filters 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 DELVE1-SOUT ACS/WFC ACCUM WFC F814W 1 1181 S PATTERN 2 1-2; PAR 2 HEAST see below WITH 1 (3806 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS F814W 1 1181 S S (4002 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 DELVE1-SOUT ACS/WFC ACCUM WFC F606W 1 570 S PAR 4 WITH 3 HEAST see below (681 S) Comments: Single 606 exposure to complement the other four from the first visit ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFC3/UVI ACCUM UVIS F606W 1 688 S S see below (723 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 | ------------------------------------------------------------------------------------------------------------------------------------ DELVE1-SOUTHEAST 1 ACS/WFC ACCUM WFC F814W 1 none none none 1 1121.0 S DELVE1-SOUTHEAST 1 ACS/WFC ACCUM WFC F814W 2 none none none 1 1121.0 S DELVE1-SOUTHEAST 1 ACS/WFC ACCUM WFC F814W 3 none none none 2 1564.0 S ANY 2 WFC3/UVI ACCUM UVIS F814W 1 none none none 1 N/A S ANY 2 WFC3/UVI ACCUM UVIS F814W 2 none none none 1 1247.0 S S ANY 2 WFC3/UVI ACCUM UVIS F814W 3 none none none 2 1574.0 S S DELVE1-SOUTHEAST 3 ACS/WFC ACCUM WFC F606W none none none none 2 681.0 S ANY 4 WFC3/UVI ACCUM UVIS F606W none none none none 2 723.0 S S 17787( 3) - 17-Oct-2024 15:02:46 - [ 10] Visit: 06 (SW_606814_Visit) Visit Requirements: SAME ORIENT AS 03 On Hold Comments: Additional Comments: Southwestern pointing; one orbit of entirely F814W imaging with UVIS F814 cpar; one orbit of F606W +F814W with UVIS cpar on both filters 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 DELVE1-SOUT ACS/WFC ACCUM WFC F814W 1 1181 S PATTERN 2 1-2; PAR 2 HWEST see below WITH 1 (3806 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS F814W 1 1181 S S (4002 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 DELVE1-SOUT ACS/WFC ACCUM WFC F606W 1 570 S PAR 4 WITH 3 HWEST see below (681 S) Comments: Single 606 exposure to complement the other four from the first visit ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFC3/UVI ACCUM UVIS F606W 1 688 S S see below (723 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 | ------------------------------------------------------------------------------------------------------------------------------------ DELVE1-SOUTHWEST 1 ACS/WFC ACCUM WFC F814W 1 none none none 1 1121.0 S DELVE1-SOUTHWEST 1 ACS/WFC ACCUM WFC F814W 2 none none none 1 1121.0 S DELVE1-SOUTHWEST 1 ACS/WFC ACCUM WFC F814W 3 none none none 2 1564.0 S ANY 2 WFC3/UVI ACCUM UVIS F814W 1 none none none 1 N/A S ANY 2 WFC3/UVI ACCUM UVIS F814W 2 none none none 1 1247.0 S S ANY 2 WFC3/UVI ACCUM UVIS F814W 3 none none none 2 1574.0 S S DELVE1-SOUTHWEST 3 ACS/WFC ACCUM WFC F606W none none none none 2 681.0 S ANY 4 WFC3/UVI ACCUM UVIS F606W none none none none 2 723.0 S S 17787( 3) - 17-Oct-2024 15:02:46 - [ 11] Summary Form for Proposal 17787 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS, WFC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PAR 2 WITH 1, PAR 4 WITH 3, PATTERN 1 1-2, PATTERN 2 1-2, SAME ORIENT AS 01, SAME ORIENT AS 02, SAME ORIENT AS 03 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names ANY, DELVE1-NORTH, DELVE1-SOUTHEAST, DELVE1-SOUTHWEST ------------------------------------------------------------------------------------------------------------------------------------