17149( 5) - 13-Oct-2022 15:55:35 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17149 Version: 5 Check-in Time: 13-Oct-2022 15:55:35 STScI Edit Number: 0 Title Characterizing the unusual star cluster population in a candidate dark matter free galaxy ------------------------------------------------------------------------------------ Type Cycle GO 30 ------------------------------------------------------------------------------------ Investigators Contact? PI: Prof. Aaron Romanowsky San Jose State Univ. Research Foundation Y CoI: Dr. Steven Janssens Swinburne University of Technology N CoI: Dr. Shany Danieli Princeton University N CoI: Prof. Jean P. Brodie University of California - Santa Cruz N CoI: Prof. Pieter van Dokkum Yale University N CoI: Enrique Cabrera San Jose State Univ. Research Foundation N CoI: Jonah Gannon Swinburne University of Technology N CoI: Dr. Anna Ferre-Mateu Instituto de Astrofisica de Canarias N CoI: Dr. Duncan A. Forbes Swinburne University of Technology N CoI: Maria Luisa Buzzo Swinburne University of Technology N ------------------------------------------------------------------------------------ Abstract We propose to characterize the star cluster population of the Fornax cluster low-surface brightness dwarf galaxy FCC 224. Current data suggest that the clusters are over-luminous relative to a standard globular cluster luminosity function (GCLF) -- missing the bulk of the expected clusters at faint magnitudes. This top-heavy LF has been seen previously in two old, dark matter free galaxies, NGC 1052-DF2 and -DF4, and is understood to be closely connected to the formation of these galaxies without dark matter. FCC 224 may therefore be only the third known example of this puzzling class of galaxies, and the first in a different environment from the NGC 1052 group. We will test definitively the resemblance of this galaxy's cluster population to those of DF2/DF4, where the clusters also have unusually large sizes and are further accompanied by a smaller population of "normal" clusters with a GCLF peak at the standard luminosity. Confirming these peculiarities in FCC 224 would complement deeper spectroscopic follow-up to test for the presence of dark matter, would potentially pave the way for using GCLF photometry to efficiently identify more dark-matter-free galaxy candidates, and would provide additional leverage on understanding star cluster formation in general. ------------------------------------------------------------------------------------ Observations Description ------------------------ This program studies the low-surface-brightness dwarf galaxy FCC 224 in the Fornax cluster with two-band imaging (WFC3UVIS F475X, F814W). The primary goals relate to its system of star clusters: their luminosities, colors, sizes, and radial density profile. The diffuse starlight will also be studied (density profile, color, surface brightness flucutations as a distance metric). The goal of the star cluster photometry is S/N ~ 20 for magnitude and size measurements down to F475X ~ 26.5 and F814W ~ 25.2 (corresponding to ~1.5 mags fainter than the standard GCLF peak). For the brightest clusters (F555W ~ 22.5-24), an additional goal is to be able to measure a color spread at the 17149( 5) - 13-Oct-2022 15:55:35 - [ 2] ~0.01 mag level, requiring S/N ~ 100 or better, with well-controlled flat-fielding. Exposures in each field consist of one orbit per filter, using a four-point dither pattern with unrestricted orient ranges. The galaxy is placed on the UVIS1 chip with POS TARG offsets to prevent Dragon's Breath from stars close to the FOV, given an anticipated March 2023 observing window. A change in the observing window may require a different offset. The offset into the A quadrant also minimizes potential problems from droplets, although these are not expected to impact differential photometry. FLASH is included to allow for low sky backgrounds in the ~600 sec exposures. ------------------------------------------------------------------------------------ 17149( 5) - 13-Oct-2022 15:55:35 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 FCC224 GALAXY, DWARF RA=03H39M32.7060S, J2000 V = 17 star cluster magnitudes F555W ~ ELLIPTICAL, DWARF DEC=-31D47'31.08" 22 - 27 SPHEROIDAL Reference Frame: Other: SIMBAD Comments: Object coordinates from Legacy g-band imaging. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2015.5 0.0 0.0 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 17149( 5) - 13-Oct-2022 15:55:35 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.173 Line_Spacing 0.112 Coordinate_Frame POS-TARG Pattern_Orient 23.884 Angle_Between_Sides 81.785 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-LINE-3PT Pattern_Purpose DITHER Number_Of_Points 3 Point_Spacing 0.135 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 46.84 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 3 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-MOS-DITH-LINE WFC3-UVIS-MOS-DITH-LINE Pattern_Purpose DITHER DITHER Number_Of_Points 2 2 Point_Spacing 2.4 0.119 Line_Spacing Coordinate_Frame POS-TARG POS-TARG Pattern_Orient 85.754 33.606 Angle_Between_Sides Center_Pattern YES NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 4 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-MOS-DITH-LINE WFC3-UVIS-MOS-DITH-LINE Pattern_Purpose DITHER DITHER Number_Of_Points 2 2 Point_Spacing 2.4 0.119 Line_Spacing Coordinate_Frame POS-TARG POS-TARG Pattern_Orient 85.754 33.606 Angle_Between_Sides Center_Pattern NO NO Pattern_Comments: Center Pattern turned off to allow POS ARG offset in Exposure specifications. 17149( 5) - 13-Oct-2022 15:55:35 - [ 5] Patterns ------------------------------------------------------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------------------------------------------------------ 17149( 5) - 13-Oct-2022 15:55:35 - [ 6] Visit: 01 (FCC 224 single visit) 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 FCC224 WFC3/UVI ACCUM UVIS1 F475X FLASH=5 1 597 S POS TARG -25, -5; S (2388 S) PATTERN 4 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 FCC224 WFC3/UVI ACCUM UVIS1 F814W FLASH=10 1 593 S PATTERN 4 2 S (2372 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 | ------------------------------------------------------------------------------------------------------------------------------------ FCC224 1 WFC3/UVI ACCUM UVIS1 F475X 1 1 none none 1 N/A S FCC224 1 WFC3/UVI ACCUM UVIS1 F475X 1 2 none none 1 N/A S FCC224 1 WFC3/UVI ACCUM UVIS1 F475X 2 1 none none 1 N/A S FCC224 1 WFC3/UVI ACCUM UVIS1 F475X 2 2 none none 1 N/A S FCC224 2 WFC3/UVI ACCUM UVIS1 F814W 1 1 none none 2 N/A S FCC224 2 WFC3/UVI ACCUM UVIS1 F814W 1 2 none none 2 N/A S FCC224 2 WFC3/UVI ACCUM UVIS1 F814W 2 1 none none 2 N/A S FCC224 2 WFC3/UVI ACCUM UVIS1 F814W 2 2 none none 2 N/A S 17149( 5) - 13-Oct-2022 15:55:35 - [ 7] Summary Form for Proposal 17149 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=10, FLASH=5 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 4 1, PATTERN 4 2, POS TARG -25, -5 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F475X, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names FCC224 ------------------------------------------------------------------------------------------------------------------------------------