17712( 4) - 08-Oct-2024 14:47:44 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17712 Version: 4 Check-in Time: 08-Oct-2024 14:47:44 STScI Edit Number: 1 Title Elucidating the Nature of a 'Starless' Dark Matter Halo Near M94 ------------------------------------------------------------------------------------ Type Cycle GO 32 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Alejandro Benitez-Llambay University of Milano-Bicocca Y CoI: Dr. Rachael L Beaton Space Telescope Science Institute Y CoI: Dr. Andrew J. Fox Space Telescope Science Institute - ESA Y CoI: Dr. Elena D'Onghia University of Wisconsin - Madison N CoI: Prof. Julio Navarro University of Victoria N CoI: Dr. Gagandeep Singh Anand Space Telescope Science Institute Y ------------------------------------------------------------------------------------ Abstract Observations with the FAST radio telescope recently detected a marginally resolved 21 cm HI cloud (named Cloud-9) near the M94 galaxy without an optical counterpart down to the surface brightness limit of the DESI Imaging Legacy Survey (~29.5 mag/arcsec^2 in the g band). Unlike previous candidate "dark" HI clouds, all known properties of Cloud-9 are consistent with RELHICs, namely starless dark matter halos filled with gas in hydrostatic equilibrium and thermal equilibrium with the cosmic ultraviolet background. However, the main doubts about its true nature concern the relatively poor angular resolution of the FAST data and the uncomfortably large upper limit in the stellar mass of any luminous stellar counterpart, M_* <= 10^5 Msun, a value comparable to the stellar mass of nearby HI-rich dwarfs. We thus propose to carry out deep photometric observations (8 orbits) with the HST/ACS instrument to bring down constraints to the stellar mass of this object to M_* < 10^4 Msun (and possibly 10^{3.5} Msun) and elucidate the true nature of Cloud-9. Either outcome will be important: (i) if we do not detect a stellar counterpart, we will reinforce the RELHIC interpretation for this system while confirming a cornerstone prediction of the LCDM model, namely the existence of starless collapsed dark matter structures on sub-galactic mass scales; (ii) if we do detect a stellar counterpart, we will have uncovered the faintest HI-rich dwarf galaxy known outside the Local Group. ------------------------------------------------------------------------------------ Observations Description ------------------------ This program target a potential satellite galaxy of M94 for analysis of its resolved stellar populations. There is a chance the satellite is a LCDM RELHIC (a starless cloud containing just gas and dark matter), in which case there will be no stars seen in the images. This 8-orbit program is broken up into 4 2-orbit visits, with equal amounts of time to F606W and F814W with both ACS/WFC (prime, main target) and WFC3/UVIS (parallel, for analysis of a background field). Orient constraints (specified in Phase I) are present to obtain an optimal background field and avoid a bright foreground star, but can be adjusted for scheduling if needed. 17712( 4) - 08-Oct-2024 14:47:44 - [ 2] The dither pattern adopted is the 5x5 pixel ACS-WFC-DITHER-LINE pattern to optimize rejection of bad pixels/columns/artifacts in ACS/WFC. The dither patter is implemented via POS TARGs. ------------------------------------------------------------------------------------ 17712( 4) - 08-Oct-2024 14:47:44 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 M94-CL9 GALAXY, DWARF COMPACT RA=12H51M51.3000S, J2000 V = 25 DEC=+40D18'5.00" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 17712( 4) - 08-Oct-2024 14:47:44 - [ 4] Visit: 01 Visit Requirements: ORIENT 223D TO 227 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 M94-CL9 ACS/WFC ACCUM WFC1-FIX F606W 1 1118 S PAR 2 WITH 1 (1118 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS F606W 1 1118 S S (1118 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 M94-CL9 ACS/WFC ACCUM WFC1-FIX F814W 1 1118 S PAR 4 WITH 3 (1118 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFC3/UVI ACCUM UVIS F814W 1 1118 S S (1118 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 M94-CL9 ACS/WFC ACCUM WFC1-FIX F606W 1 1141 S POS TARG 0.247, 0.267; (1141 S) PAR 6 WITH 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 ANY WFC3/UVI ACCUM UVIS F606W 1 1141 S S (1141 S) ------------------------------------------------------------------------------------------------------------------------------------ 7 M94-CL9 ACS/WFC ACCUM WFC1-FIX F814W 1 1141 S SAME POS AS 5; PAR 8 (1141 S) WITH 7 ------------------------------------------------------------------------------------------------------------------------------------ 8 ANY WFC3/UVI ACCUM UVIS F814W 1 1141 S S (1141 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 | ------------------------------------------------------------------------------------------------------------------------------------ M94-CL9 1 ACS/WFC ACCUM WFC1-FIX F606W none none none none 1 N/A ANY 2 WFC3/UVI ACCUM UVIS F606W none none none none 1 N/A S M94-CL9 3 ACS/WFC ACCUM WFC1-FIX F814W none none none none 1 N/A ANY 4 WFC3/UVI ACCUM UVIS F814W none none none none 1 N/A S M94-CL9 5 ACS/WFC ACCUM WFC1-FIX F606W none none none none 2 N/A ANY 6 WFC3/UVI ACCUM UVIS F606W none none none none 2 N/A S M94-CL9 7 ACS/WFC ACCUM WFC1-FIX F814W none none none none 2 N/A ANY 8 WFC3/UVI ACCUM UVIS F814W none none none none 2 N/A S 17712( 4) - 08-Oct-2024 14:47:44 - [ 5] Visit: 02 Visit Requirements: ORIENT 223D TO 227 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 M94-CL9 ACS/WFC ACCUM WFC1-FIX F606W 1 1118 S PAR 2 WITH 1 (1118 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS F606W 1 1118 S S (1118 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 M94-CL9 ACS/WFC ACCUM WFC1-FIX F814W 1 1118 S PAR 4 WITH 3 (1118 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFC3/UVI ACCUM UVIS F814W 1 1118 S S (1118 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 M94-CL9 ACS/WFC ACCUM WFC1-FIX F606W 1 1141 S POS TARG 0.247, 0.267; (1141 S) PAR 6 WITH 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 ANY WFC3/UVI ACCUM UVIS F606W 1 1141 S S (1141 S) ------------------------------------------------------------------------------------------------------------------------------------ 7 M94-CL9 ACS/WFC ACCUM WFC1-FIX F814W 1 1141 S SAME POS AS 5; PAR 8 (1141 S) WITH 7 ------------------------------------------------------------------------------------------------------------------------------------ 8 ANY WFC3/UVI ACCUM UVIS F814W 1 1141 S S (1141 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 | ------------------------------------------------------------------------------------------------------------------------------------ M94-CL9 1 ACS/WFC ACCUM WFC1-FIX F606W none none none none 1 N/A ANY 2 WFC3/UVI ACCUM UVIS F606W none none none none 1 N/A S M94-CL9 3 ACS/WFC ACCUM WFC1-FIX F814W none none none none 1 N/A ANY 4 WFC3/UVI ACCUM UVIS F814W none none none none 1 N/A S M94-CL9 5 ACS/WFC ACCUM WFC1-FIX F606W none none none none 2 N/A ANY 6 WFC3/UVI ACCUM UVIS F606W none none none none 2 N/A S M94-CL9 7 ACS/WFC ACCUM WFC1-FIX F814W none none none none 2 N/A ANY 8 WFC3/UVI ACCUM UVIS F814W none none none none 2 N/A S 17712( 4) - 08-Oct-2024 14:47:44 - [ 6] Visit: 03 Visit Requirements: ORIENT 223D TO 227 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 M94-CL9 ACS/WFC ACCUM WFC1-FIX F606W 1 1118 S PAR 2 WITH 1 (1118 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS F606W 1 1118 S S (1118 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 M94-CL9 ACS/WFC ACCUM WFC1-FIX F814W 1 1118 S PAR 4 WITH 3 (1118 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFC3/UVI ACCUM UVIS F814W 1 1118 S S (1118 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 M94-CL9 ACS/WFC ACCUM WFC1-FIX F606W 1 1141 S POS TARG 0.247, 0.267; (1141 S) PAR 6 WITH 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 ANY WFC3/UVI ACCUM UVIS F606W 1 1141 S S (1141 S) ------------------------------------------------------------------------------------------------------------------------------------ 7 M94-CL9 ACS/WFC ACCUM WFC1-FIX F814W 1 1141 S SAME POS AS 5; PAR 8 (1141 S) WITH 7 ------------------------------------------------------------------------------------------------------------------------------------ 8 ANY WFC3/UVI ACCUM UVIS F814W 1 1141 S S (1141 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 | ------------------------------------------------------------------------------------------------------------------------------------ M94-CL9 1 ACS/WFC ACCUM WFC1-FIX F606W none none none none 1 N/A ANY 2 WFC3/UVI ACCUM UVIS F606W none none none none 1 N/A S M94-CL9 3 ACS/WFC ACCUM WFC1-FIX F814W none none none none 1 N/A ANY 4 WFC3/UVI ACCUM UVIS F814W none none none none 1 N/A S M94-CL9 5 ACS/WFC ACCUM WFC1-FIX F606W none none none none 2 N/A ANY 6 WFC3/UVI ACCUM UVIS F606W none none none none 2 N/A S M94-CL9 7 ACS/WFC ACCUM WFC1-FIX F814W none none none none 2 N/A ANY 8 WFC3/UVI ACCUM UVIS F814W none none none none 2 N/A S 17712( 4) - 08-Oct-2024 14:47:44 - [ 7] Visit: 04 Visit Requirements: ORIENT 223D TO 227 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 M94-CL9 ACS/WFC ACCUM WFC1-FIX F606W 1 1118 S PAR 2 WITH 1 (1118 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS F606W 1 1118 S S (1118 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 M94-CL9 ACS/WFC ACCUM WFC1-FIX F814W 1 1118 S PAR 4 WITH 3 (1118 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFC3/UVI ACCUM UVIS F814W 1 1118 S S (1118 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 M94-CL9 ACS/WFC ACCUM WFC1-FIX F606W 1 1141 S POS TARG 0.247, 0.267; (1141 S) PAR 6 WITH 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 ANY WFC3/UVI ACCUM UVIS F606W 1 1141 S S (1141 S) ------------------------------------------------------------------------------------------------------------------------------------ 7 M94-CL9 ACS/WFC ACCUM WFC1-FIX F814W 1 1141 S SAME POS AS 5; PAR 8 (1141 S) WITH 7 ------------------------------------------------------------------------------------------------------------------------------------ 8 ANY WFC3/UVI ACCUM UVIS F814W 1 1141 S S (1141 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 | ------------------------------------------------------------------------------------------------------------------------------------ M94-CL9 1 ACS/WFC ACCUM WFC1-FIX F606W none none none none 1 N/A ANY 2 WFC3/UVI ACCUM UVIS F606W none none none none 1 N/A S M94-CL9 3 ACS/WFC ACCUM WFC1-FIX F814W none none none none 1 N/A ANY 4 WFC3/UVI ACCUM UVIS F814W none none none none 1 N/A S M94-CL9 5 ACS/WFC ACCUM WFC1-FIX F606W none none none none 2 N/A ANY 6 WFC3/UVI ACCUM UVIS F606W none none none none 2 N/A S M94-CL9 7 ACS/WFC ACCUM WFC1-FIX F814W none none none none 2 N/A ANY 8 WFC3/UVI ACCUM UVIS F814W none none none none 2 N/A S 17712( 4) - 08-Oct-2024 14:47:44 - [ 8] Summary Form for Proposal 17712 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS, WFC1-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 223D TO 227 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 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names ANY, M94-CL9 ------------------------------------------------------------------------------------------------------------------------------------