16916( 5) - 14-Mar-2023 21:11:43 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 16916 Version: 5 Check-in Time: 14-Mar-2023 21:11:43 STScI Edit Number: 1 Title Discovery of 3 Ultra-Faint Dwarf Candidates Outside the MW Halo ------------------------------------------------------------------------------------ Type Cycle GO 29 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Kristen B W McQuinn Rutgers the State University of New Jersey Y CoI: Dr. Yao-Yuan Mao University of Utah N CoI: Dr. Andrew Eugene Dolphin Raytheon Technologies N CoI: Prof. David Shih Rutgers the State University of New Jersey N CoI: Prof. Matthew Buckley Rutgers the State University of New Jersey N ------------------------------------------------------------------------------------ Abstract The lowest mass galaxies known to date - aptly named 'ultra-faint dwarf galaxies' - orbit the Milky Way (MW) as satellites. Follow-up study of these objects have revealed systems that are the oldest, most metal-poor, and most dark matter-dominated galaxies known. They hold the potential for constraining dark matter on small scales, placing limits on the mass threshold for successful galaxy formation, and defining the impact reionization has on small galaxy halos. Such galaxies are predicted to be present in large numbers in the Local Group (and throughout the universe), yet they have belied detection due the challenges in finding instrinsically small and faint systems in a very big sky. We have discovered three ultra-faint dwarf galaxy candidates in the Dark Energy Spectrscopic Instrument (DESI) Legacy imaging data located outside the halo of the MW at distances estimated to be between 0.4-0.7 Mpc. In contrast to the population of ultra-faint dwarfs discovered as satellites of the MW, these galaxy candidates appear to be outside the halo of the MW system, providing a unique opportunity to test galaxy formation theories without the competing effects of a halo environment. We request 1 orbit of HST per target to confirm their detection, measure secure distances, and determine their structural properties. Their properties will be compared with those of ultra-faint dwarf satellites of MW and M31, as well as isolated very low-mass galaxies. We will determine their star formation histories from their resolved stellar populations to test whether they are quenched, have extended (or delayed) star formation over cosmic times, or distinct characteristics. ------------------------------------------------------------------------------------ Observations Description ------------------------ The observations included ACS/WFC and WFC3/UVIS imaging in the F606W and F814W filters. The data will be used to confirm that the targets are galaxies, measure the distances to the systems from resolved stars (TRGB and/or Horizontal Branch methods), characterize the stellar properites (star formation histories and metallicities), and measure the structural parameters of the galaxies. The parallel pointings will allow us to observe a field region next to our targets. We will thus be able to estimate more precisely the number of background/foreground contaminants present in our ACS fields. 16916( 5) - 14-Mar-2023 21:11:43 - [ 2] Each of the 3 targets will be observed for 1 orbit. We use a 5x5 pixel dither implemented using pos-targ (equivalent to the ACS WFC DITHER LINE pattern #14) to reject cosmic rays and handle hot pixels. The first pointing is executed with both filters in ACS and with both filters in WFC3 parallel fields. After the dither, the observations are then repeated. The exposure time per orbit is split roughly equally between the F606W and F814W filters. In order to obtain 4 exposures in both ACS and WFC3 in one orbit and accomodate buffer dumps during exposures, we have added a special requirement to the visibility interval (following the counsel of the STScI help desk). This did not impact schedulablity appreciably. Each visit is 1-orbit. We have place ORIENT constraints to ensure we maximum coverage of the stellar disk and prevent the galaxy centers from falling in the ACS chip gap, while avoiding nearby bright stars. ------------------------------------------------------------------------------------ 16916( 5) - 14-Mar-2023 21:11:43 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 LEO-M GALAXY, DWARF RA=11H05M18.9449S, J2000 V = 17 SPHEROIDAL DEC=+25D20'58.57" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 2 LEO-K GALAXY, DWARF RA=09H24M4.2998S, J2000 V = 17 SPHEROIDAL DEC=+16D30'24.05" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 3 PEGASUS-W GALAXY, DWARF RA=23H53M14.2288S, J2000 V = 17 SPHEROIDAL DEC=+22D05'35.54" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 16916( 5) - 14-Mar-2023 21:11:43 - [ 4] Visit: 01 (LEO M) Visit Requirements: ORIENT 255D TO 290 D; VISIBILITY INTERVAL 3285 S 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 LEO-M ACS/WFC ACCUM WFC F606W 1 350 S (350 PAR 2 WITH 1 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS F606W 1 410 S (410 S S) ------------------------------------------------------------------------------------------------------------------------------------ 3 LEO-M ACS/WFC ACCUM WFC F814W 1 670 S (670 PAR 4 WITH 3 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFC3/UVI ACCUM UVIS F814W 1 730 S (730 S S) ------------------------------------------------------------------------------------------------------------------------------------ 5 LEO-M ACS/WFC ACCUM WFC F606W 1 670 S (670 POS TARG 0.247, 0.267; S) PAR 6 WITH 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 ANY WFC3/UVI ACCUM UVIS F606W 1 730 S (730 S S) ------------------------------------------------------------------------------------------------------------------------------------ 7 LEO-M ACS/WFC ACCUM WFC F814W 1 375 S (375 SAME POS AS 5; PAR 8 S) WITH 7 ------------------------------------------------------------------------------------------------------------------------------------ 8 ANY WFC3/UVI ACCUM UVIS F814W FLASH=11 1 410 S (410 S 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 | ------------------------------------------------------------------------------------------------------------------------------------ LEO-M 1 ACS/WFC ACCUM WFC F606W none none none none 1 N/A ANY 2 WFC3/UVI ACCUM UVIS F606W none none none none 1 N/A S LEO-M 3 ACS/WFC ACCUM WFC F814W none none none none 1 N/A ANY 4 WFC3/UVI ACCUM UVIS F814W none none none none 1 N/A S LEO-M 5 ACS/WFC ACCUM WFC F606W none none none none 1 N/A ANY 6 WFC3/UVI ACCUM UVIS F606W none none none none 1 N/A S LEO-M 7 ACS/WFC ACCUM WFC F814W none none none none 1 N/A ANY 8 WFC3/UVI ACCUM UVIS F814W none none none none 1 N/A S 16916( 5) - 14-Mar-2023 21:11:43 - [ 5] Visit: 02 (LEO K) Visit Requirements: ORIENT 75D TO 95 D; VISIBILITY INTERVAL 3285 S 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 LEO-K ACS/WFC ACCUM WFC F606W 1 350 S (350 PAR 2 WITH 1 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS F606W 1 410 S (410 S S) ------------------------------------------------------------------------------------------------------------------------------------ 3 LEO-K ACS/WFC ACCUM WFC F814W 1 670 S (670 PAR 4 WITH 3 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFC3/UVI ACCUM UVIS F814W 1 730 S (730 S S) ------------------------------------------------------------------------------------------------------------------------------------ 5 LEO-K ACS/WFC ACCUM WFC F606W 1 670 S (670 POS TARG 0.247, 0.267; S) PAR 6 WITH 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 ANY WFC3/UVI ACCUM UVIS F606W 1 730 S (730 S S) ------------------------------------------------------------------------------------------------------------------------------------ 7 LEO-K ACS/WFC ACCUM WFC F814W 1 375 S (375 SAME POS AS 5; PAR 8 S) WITH 7 ------------------------------------------------------------------------------------------------------------------------------------ 8 ANY WFC3/UVI ACCUM UVIS F814W FLASH=11 1 410 S (410 S 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 | ------------------------------------------------------------------------------------------------------------------------------------ LEO-K 1 ACS/WFC ACCUM WFC F606W none none none none 1 N/A ANY 2 WFC3/UVI ACCUM UVIS F606W none none none none 1 N/A S LEO-K 3 ACS/WFC ACCUM WFC F814W none none none none 1 N/A ANY 4 WFC3/UVI ACCUM UVIS F814W none none none none 1 N/A S LEO-K 5 ACS/WFC ACCUM WFC F606W none none none none 1 N/A ANY 6 WFC3/UVI ACCUM UVIS F606W none none none none 1 N/A S LEO-K 7 ACS/WFC ACCUM WFC F814W none none none none 1 N/A ANY 8 WFC3/UVI ACCUM UVIS F814W none none none none 1 N/A S 16916( 5) - 14-Mar-2023 21:11:43 - [ 6] Visit: 03 (PEGASUS W) Visit Requirements: ORIENT 225D TO 249 D; VISIBILITY INTERVAL 3285 S 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-W ACS/WFC ACCUM WFC F606W 1 350 S (350 PAR 2 WITH 1 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS F606W 1 410 S (410 S S) ------------------------------------------------------------------------------------------------------------------------------------ 3 PEGASUS-W ACS/WFC ACCUM WFC F814W 1 670 S (670 PAR 4 WITH 3 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFC3/UVI ACCUM UVIS F814W 1 730 S (730 S S) ------------------------------------------------------------------------------------------------------------------------------------ 5 PEGASUS-W ACS/WFC ACCUM WFC F606W 1 670 S (670 POS TARG 0.247, 0.267; S) PAR 6 WITH 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 ANY WFC3/UVI ACCUM UVIS F606W 1 730 S (730 S S) ------------------------------------------------------------------------------------------------------------------------------------ 7 PEGASUS-W ACS/WFC ACCUM WFC F814W 1 375 S (375 SAME POS AS 5; PAR 8 S) WITH 7 ------------------------------------------------------------------------------------------------------------------------------------ 8 ANY WFC3/UVI ACCUM UVIS F814W FLASH=11 1 410 S (410 S 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-W 1 ACS/WFC ACCUM WFC F606W none none none none 1 N/A ANY 2 WFC3/UVI ACCUM UVIS F606W none none none none 1 N/A S PEGASUS-W 3 ACS/WFC ACCUM WFC F814W none none none none 1 N/A ANY 4 WFC3/UVI ACCUM UVIS F814W none none none none 1 N/A S PEGASUS-W 5 ACS/WFC ACCUM WFC F606W none none none none 1 N/A ANY 6 WFC3/UVI ACCUM UVIS F606W none none none none 1 N/A S PEGASUS-W 7 ACS/WFC ACCUM WFC F814W none none none none 1 N/A ANY 8 WFC3/UVI ACCUM UVIS F814W none none none none 1 N/A S 16916( 5) - 14-Mar-2023 21:11:43 - [ 7] Visit: 04 (LEO K) Visit Requirements: ORIENT 75D TO 95 D; VISIBILITY INTERVAL 3285 S 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 LEO-K ACS/WFC ACCUM WFC F606W 1 350 S (350 PAR 2 WITH 1 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS F606W 1 410 S (410 S S) ------------------------------------------------------------------------------------------------------------------------------------ 3 LEO-K ACS/WFC ACCUM WFC F814W 1 670 S (670 PAR 4 WITH 3 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFC3/UVI ACCUM UVIS F814W 1 730 S (730 S S) ------------------------------------------------------------------------------------------------------------------------------------ 5 LEO-K ACS/WFC ACCUM WFC F606W 1 670 S (670 POS TARG 0.247, 0.267; S) PAR 6 WITH 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 ANY WFC3/UVI ACCUM UVIS F606W 1 730 S (730 S S) ------------------------------------------------------------------------------------------------------------------------------------ 7 LEO-K ACS/WFC ACCUM WFC F814W 1 375 S (375 SAME POS AS 5; PAR 8 S) WITH 7 ------------------------------------------------------------------------------------------------------------------------------------ 8 ANY WFC3/UVI ACCUM UVIS F814W FLASH=11 1 410 S (410 S 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 | ------------------------------------------------------------------------------------------------------------------------------------ LEO-K 1 ACS/WFC ACCUM WFC F606W none none none none 1 N/A ANY 2 WFC3/UVI ACCUM UVIS F606W none none none none 1 N/A S LEO-K 3 ACS/WFC ACCUM WFC F814W none none none none 1 N/A ANY 4 WFC3/UVI ACCUM UVIS F814W none none none none 1 N/A S LEO-K 5 ACS/WFC ACCUM WFC F606W none none none none 1 N/A ANY 6 WFC3/UVI ACCUM UVIS F606W none none none none 1 N/A S LEO-K 7 ACS/WFC ACCUM WFC F814W none none none none 1 N/A ANY 8 WFC3/UVI ACCUM UVIS F814W none none none none 1 N/A S 16916( 5) - 14-Mar-2023 21:11:43 - [ 8] Summary Form for Proposal 16916 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS, WFC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=11 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 225D TO 249 D, ORIENT 255D TO 290 D, ORIENT 75D TO 95 D, PAR 2 WITH 1, PAR 4 WITH 3, PAR 6 WITH 5, PAR 8 WITH 7, POS TARG 0.247, 0.267, SAME POS AS 5, VISIBILITY INTERVAL 3285 S ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names ANY, LEO-K, LEO-M, PEGASUS-W ------------------------------------------------------------------------------------------------------------------------------------