17316( 2) - 02-Jun-2023 16:50:41 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17316 Version: 2 Check-in Time: 02-Jun-2023 16:50:41 STScI Edit Number: 0 Title Quenching in the lowest mass galaxies at the edge of the Local Group ------------------------------------------------------------------------------------ Type Cycle GO 31 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Michael Gordon Jones University of Arizona Y CoI: Prof. David J. Sand University of Arizona N CoI: Dr. Kristine Spekkens Royal Military College of Canada N CoI: Dr. Catherine Fielder University of Arizona N CoI: Dr. Ananthan Karunakaran University of Toronto N CoI: Dr. Burcin Mutlu-Pakdil Dartmouth College N CoI: Dr. Paul Bennet Space Telescope Science Institute N CoI: Dr. Denija Crnojevic University of Tampa N ------------------------------------------------------------------------------------ Abstract We request 10.5 h of VLA D-array time and 2 HST orbits in order to constrain the neutral gas content and stellar populations of three recently discovered ultra-faint dwarf galaxies (UFDs) at the edge of the Local Group. UFDs are the lowest mass galaxies that exist and our standard framework of galaxy evolution and cosmology predicts that they should be permanently quenched by cosmic reionization. However, the discovery of Pegasus W, a UFD that has evidence for recent star formation, has called this longstanding prediction into question. Here we target Pegasus W and two other recently discovered UFDs to conclusively address whether or not they contain HI gas, which could provide fuel for ongoing star formation, and whether there is evidence for populations of young stars in their color--magnitude diagrams. If they do contain gas, these UFDs may be fainter analogs of the Phoenix dwarf, which appears to be in the process of losing its gas. Discovering HI gas or young stellar populations in (or around) any of these systems would reinforce the recent findings for Pegasus W and would force a rethink of our longstanding assumptions about reionization and the evolution of the lowest mass galaxies. ------------------------------------------------------------------------------------ Observations Description ------------------------ These observations focus on two ultra-faint dwarf galaxies at the edge of the Local Group, and near M31's virial radius in particular. The goal is to study their star formation history with HST and improve our understanding of quenching of the smallest galaxies in this unique environment. We model our strategy after the recent successful observations of Pegasus W. We request the ACS/WFC imager for its wider field of view than WFC3 and its better sensitivity in our chosen imaging bands. Also, we will image in the F606W and F814W filters to produce a color magnitude diagram (CMD) of our dwarfs; these filters are the standard for nearby resolved stellar population work, and are identical to those used in Pegasus W. We also request WFC3-UVIS parallel imaging in the same filters (F606W, F814W). This will allow us to observe a field region next to our two dwarf targets (albeit to slightly brighter limits), and get a better statistical handle on the number of background/foreground contaminants in the 17316( 2) - 02-Jun-2023 16:50:41 - [ 2] CMD (which we know will have some Milky Way contamination, given the galactic latitude of -30 degrees). To get both bands in a single orbit (with ~1200s total integration per filter), we will obtain two exposures per filter, with a standard dither line offset between them to aid with cosmic ray and chip defect removal. If a given stellar system can safely fit on a single chip, we will position it accordingly. We may place orient constraints on our ACS imaging to avoid bright stars and potential image artifacts. ------------------------------------------------------------------------------------ 17316( 2) - 02-Jun-2023 16:50:41 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 PEGASUS-V GALAXY, DWARF RA=23H18M27.8000S, J2000 V = 23.0 +/- 0.2 SPHEROIDAL DEC=+33D21'32.00" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 2 PISCES-VII GALAXY, DWARF RA=01H21M40.5000S, J2000 V = 23.9 +/- 0.2 SPHEROIDAL DEC=+26D23'24.00" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 17316( 2) - 02-Jun-2023 16:50:41 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 3.034 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 85.29 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 17316( 2) - 02-Jun-2023 16:50:41 - [ 5] Visit: 01 (PEGASUS-V) Visit Requirements: ORIENT 122D TO 82.5 D 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 PEGASUS-V ACS/WFC ACCUM WFC F606W 1 550 S POS TARG see below -0.48900434527053316, (966 S) 31.92974319633446; PATTERN 1 1-2; PAR 2 WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS F606W FLASH=2 1 550 S S see below (1070 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 PEGASUS-V ACS/WFC ACCUM WFC F814W 1 550 S POS TARG see below -0.48900434527053316, (1070 S) 31.92974319633446; PATTERN 1 3-4; PAR 4 WITH 3 ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFC3/UVI ACCUM UVIS F814W FLASH=5 1 550 S S see below (1240 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 | ------------------------------------------------------------------------------------------------------------------------------------ PEGASUS-V 1 ACS/WFC ACCUM WFC F606W 1 none none none 1 266.0 S PEGASUS-V 1 ACS/WFC ACCUM WFC F606W 2 none none none 1 700.0 S ANY 2 WFC3/UVI ACCUM UVIS F606W 1 none none none 1 345.0 S S ANY 2 WFC3/UVI ACCUM UVIS F606W 2 none none none 1 725.0 S S PEGASUS-V 3 ACS/WFC ACCUM WFC F814W 1 none none none 1 730.0 S PEGASUS-V 3 ACS/WFC ACCUM WFC F814W 2 none none none 1 340.0 S ANY 4 WFC3/UVI ACCUM UVIS F814W 1 none none none 1 790.0 S S ANY 4 WFC3/UVI ACCUM UVIS F814W 2 none none none 1 450.0 S S 17316( 2) - 02-Jun-2023 16:50:41 - [ 6] Visit: 02 (PISCES-VII) 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 PISCES-VII ACS/WFC ACCUM WFC F606W 1 550 S POS TARG see below -1.150775495882805, (951 S) 32.93619900745707; PATTERN 1 1-2; PAR 2 WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS F606W FLASH=2 1 550 S S see below (1055 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 PISCES-VII ACS/WFC ACCUM WFC F814W 1 550 S POS TARG see below -1.150775495882805, (1070 S) 32.93619900745707; PATTERN 1 3-4; PAR 4 WITH 3 ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFC3/UVI ACCUM UVIS F814W FLASH=5 1 550 S S see below (1240 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 | ------------------------------------------------------------------------------------------------------------------------------------ PISCES-VII 1 ACS/WFC ACCUM WFC F606W 1 none none none 1 251.0 S PISCES-VII 1 ACS/WFC ACCUM WFC F606W 2 none none none 1 700.0 S ANY 2 WFC3/UVI ACCUM UVIS F606W 1 none none none 1 330.0 S S ANY 2 WFC3/UVI ACCUM UVIS F606W 2 none none none 1 725.0 S S PISCES-VII 3 ACS/WFC ACCUM WFC F814W 1 none none none 1 730.0 S PISCES-VII 3 ACS/WFC ACCUM WFC F814W 2 none none none 1 340.0 S ANY 4 WFC3/UVI ACCUM UVIS F814W 1 none none none 1 790.0 S S ANY 4 WFC3/UVI ACCUM UVIS F814W 2 none none none 1 450.0 S S 17316( 2) - 02-Jun-2023 16:50:41 - [ 7] Summary Form for Proposal 17316 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS, WFC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=2, FLASH=5 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 122D TO 82.5 D, PAR 2 WITH 1, PAR 4 WITH 3, PATTERN 1 1-2, PATTERN 1 3-4, POS TARG -0.48900434527053316, 31.92974319633446, POS TARG -1.150775495882805, 32.93619900745707 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names ANY, PEGASUS-V, PISCES-VII ------------------------------------------------------------------------------------------------------------------------------------