16882( 4) - 07-Jan-2022 21:40:31 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 16882 Version: 4 Check-in Time: 07-Jan-2022 21:40:31 STScI Edit Number: 0 Title High-resolution ACS/WFC Imaging of Compact Stellar Systems in the Virgo Cluster in Support of JWST Cycle 1 Science ------------------------------------------------------------------------------------ Type Cycle GO 29 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Matthew Taylor NRC Herzberg Institute of Astrophysics Y CoI: Dr. Patrick Cote National Research Council of Canada N CoI: Dr. Laura Ferrarese National Research Council of Canada N CoI: Dr. Joel Roediger National Research Council of Canada N CoI: Dr. Eric W. Peng Peking University N CoI: Dr. Youkyung Ko Korea Astronomy and Space Science N Institute (KASI) CoI: Dr. Chengze Liu Peking University N CoI: Dr. Monica Valluri University of Michigan N CoI: Eugene Vasiliev University of Cambridge N CoI: Mr. Kaixiang Wang Peking University N ------------------------------------------------------------------------------------ Abstract A rich system of thousands of compact stellar systems (CSSs) including globular clusters (GCs), nuclear star clusters (NSCs), ultra-compact dwarf galaxies (UCDs), and compact elliptical galaxies (cEs) permeate the nearby (16.7 Mpc) Virgo galaxy cluster. CSSs are very useful as they are observationally easily accessible, and effectively trace the descendants of former diffuse systems disrupted in violent galaxy cluster environment. CSSs have interconnected (often galactic) formation histories, and - in a growing number of examples - have recently been found to harbor super-massive black holes (SMBHs), confirming their utility in representing remnant nuclei of formerly more massive galaxies tidally stripped of their outer stellar sheaths. These discoveries imply that CSSs may represent a rich population of targets in which to search for so-called "intermediate"-mass BHs (IMBHs) - a class whose demographics are generally unknown. A systematic search for massive BHs in CSSs in a cluster environment has been prohibitively expensive using current ground- or space-based facilities; however, this opportunity has been opened up with the imminent launch of JWST, on which >40 hours were awarded in Cycle 1 to conduct such a search. Here we propose preparatory HST+ACS/WFC3 observations to obtain high-resolution imaging for a small number of the planned JWST targets for which archival HST imaging is not available. These images will be crucial in maximizing the scientific value of the upcoming JWST observations by enabling the construction of 3D de-projected CSS luminosity profiles, a necessary component for stellar dynamical modeling and meaningfully constraining central BH properties. ------------------------------------------------------------------------------------ Observations Description ------------------------ This is a straight-forward imaging program to maximize the scientific potential of upcoming JWST Cycle 1 observations. Specifically, we request five orbits using HST+ACS/WFC to obtain deep imaging of five compact stellar systems (CSSs) in the Virgo galaxy cluster in the two F475W and F850LP filters. These filters 16882( 4) - 07-Jan-2022 21:40:31 - [ 2] are chosen to provide color informations to estimate color/metallicity profiles, given their high throughput and ability to enable precise age/metallicity estimates based on their modelled stellar populations. We choose these filters to complement the large-scale, already completed ACSVCS program (HST GO-9401). We request a single orbit for each target, where visibility for targets in Virgo is about 3200s. Working within this constreaint and being mindful of telescope overheads, we will split each visit into exposures of 800s in F475W, and 1280s in F850LP, and apply CR-SPLIT2 to aid in cosmic ray removal. These exposure times will reach depths sufficient to reach old, metal-poor stellar popluations in each filter while fitting each target into a single HST orbit. Using this setup, we run two simulations in the ACS Imaging ETC, for each filter and respective exposure time. Given that we have ground-based measured photometric profiles for all our targets, we adopt an extended source with size and luminosity corresponding to UCDe372 - our most extended and faintest target - so that the ETC estimate will be under-estimates of the expected data quality for the remaining targets. Specifically, we assume a source with a half-light radius of 0.415" and integrated g'=19.4 mag, and use a 0.1" circular aperture for signal extraction. Furthermore, we assume a Brzual + Charlot (2003) 12 Gyr-old SSP spectrum to model the expected old stellar pop0ulations of our targets. We assume E(B-V)=0.024, and otherwise standard presciptions for background levels. With this setup, we achieve S/N=100 and 150 for F475W and F850LP, respectively. Finally, for target UCD761, we will acquire on a nearby star and apply an offset so that the detector field of view will also include a nearby dwarf galaxy that has not recieved attention from a space-based telescope and thus adds ancillary science to our program. ------------------------------------------------------------------------------------ 16882( 4) - 07-Jan-2022 21:40:31 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 UCD761 EXT-CLUSTER, GLOBULAR RA=12H43M52.4180S +/- 0.1", J2000 V = 848 V = 18.52 +/- 0.01 CLUSTER, NUCLEUS DEC=+11D25'34.20" +/- 0.1" Reference Frame: ICRS Extended: NO Comments: This is the main science target, but acquisition will be done on a nearby star (target UCD761-OFFSETSTAR), and an offset will be further applied to include a nearby dwarf galaxy in the field of view. ------------------------------------------------------------------------------------------------------------------------------------ 2 UCD218 EXT-CLUSTER, GLOBULAR RA=12H26M36.4240S +/- 0.1", J2000 V = -93 V = 18.64 +/- 0.01 CLUSTER, NUCLEUS DEC=+12D55'12.88" +/- 0.1" Reference Frame: ICRS Extended: NO ------------------------------------------------------------------------------------------------------------------------------------ 3 UCD736 EXT-CLUSTER, GLOBULAR RA=12H42M51.1210S +/- 0.1", J2000 V = 536 V = 18.67 +/- 0.01 CLUSTER, NUCLEUS DEC=+11D37'16.04" +/- 0.1" Reference Frame: ICRS Extended: NO ------------------------------------------------------------------------------------------------------------------------------------ 4 UCDE372 EXT-CLUSTER, GLOBULAR RA=12H30M18.0570S, J2000 V = 1070 V = 19.22 +/- 0.01 CLUSTER, NUCLEUS DEC=+07D50'24.89" Reference Frame: ICRS Extended: NO ------------------------------------------------------------------------------------------------------------------------------------ 5 UCDE374 EXT-CLUSTER, GLOBULAR RA=12H30M20.0460S, J2000 V = 1406 V = 19.11 +/- 0.01 CLUSTER, NUCLEUS DEC=+11D55'18.68" Reference Frame: ICRS Extended: NO ------------------------------------------------------------------------------------------------------------------------------------ 8 UCD761-OFFSE UNIDENTIFIED, RA-OFF=-1.5S, DEC-OFF=28", FROM J2000 V = 13.30 T UNDESIGNATED 9 Extended: NO ------------------------------------------------------------------------------------------------------------------------------------ 9 UCD761-OFFSE STAR, UNDESIGNATED RA=12H43M56.5340S +/- 0.1", J2000 V = 13.30 +/- 0.1 TSTAR DEC=+11D26'26.58" +/- 0.1" Reference Frame: ICRS Extended: NO Comments: This is an offset star from target UCD761, meant to be acquired on, then offset from (to target UCD761-OFFSET) so that a nearby dwarf galaxy can be included as an ancillary science target. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 0.0 0.0 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 16882( 4) - 07-Jan-2022 21:40:31 - [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 16882( 4) - 07-Jan-2022 21:40:31 - [ 5] Visit: 01 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 UCD761-OFFS ACS/WFC ACCUM WFC F475W 1 800 S PATTERN 1 1-2 ET see below (770 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 UCD761-OFFS ACS/WFC ACCUM WFC F850LP 1 1280 S ET see below (1220 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 | ------------------------------------------------------------------------------------------------------------------------------------ UCD761-OFFSET 1 ACS/WFC ACCUM WFC F475W 1 none none none 1 385 S UCD761-OFFSET 1 ACS/WFC ACCUM WFC F475W 2 none none none 1 385 S UCD761-OFFSET 2 ACS/WFC ACCUM WFC F850LP 1 none none none 1 610 S UCD761-OFFSET 2 ACS/WFC ACCUM WFC F850LP 2 none none none 1 610 S 16882( 4) - 07-Jan-2022 21:40:31 - [ 6] Visit: 02 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 UCD218 ACS/WFC ACCUM WFC1-CTE F475W 1 800 S PATTERN 1 1-2 see below (770 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 UCD218 ACS/WFC ACCUM WFC1-CTE F850LP 1 1280 S see below (1220 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 | ------------------------------------------------------------------------------------------------------------------------------------ UCD218 1 ACS/WFC ACCUM WFC1-CTE F475W 1 none none none 1 385.0 S UCD218 1 ACS/WFC ACCUM WFC1-CTE F475W 2 none none none 1 385.0 S UCD218 2 ACS/WFC ACCUM WFC1-CTE F850LP 1 none none none 1 610.0 S UCD218 2 ACS/WFC ACCUM WFC1-CTE F850LP 2 none none none 1 610.0 S 16882( 4) - 07-Jan-2022 21:40:31 - [ 7] Visit: 03 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 UCD736 ACS/WFC ACCUM WFC1-CTE F475W 1 800 S PATTERN 1 1-2 see below (770 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 UCD736 ACS/WFC ACCUM WFC1-CTE F850LP 1 1280 S see below (1220 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 | ------------------------------------------------------------------------------------------------------------------------------------ UCD736 1 ACS/WFC ACCUM WFC1-CTE F475W 1 none none none 1 385 S UCD736 1 ACS/WFC ACCUM WFC1-CTE F475W 2 none none none 1 385 S UCD736 2 ACS/WFC ACCUM WFC1-CTE F850LP 1 none none none 1 610 S UCD736 2 ACS/WFC ACCUM WFC1-CTE F850LP 2 none none none 1 610 S 16882( 4) - 07-Jan-2022 21:40:31 - [ 8] Visit: 04 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 UCDE372 ACS/WFC ACCUM WFC1-CTE F475W 1 800 S PATTERN 1 1-2 see below (770 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 UCDE372 ACS/WFC ACCUM WFC1-CTE F850LP 1 1280 S see below (1220 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 | ------------------------------------------------------------------------------------------------------------------------------------ UCDE372 1 ACS/WFC ACCUM WFC1-CTE F475W 1 none none none 1 385 S UCDE372 1 ACS/WFC ACCUM WFC1-CTE F475W 2 none none none 1 385 S UCDE372 2 ACS/WFC ACCUM WFC1-CTE F850LP 1 none none none 1 610 S UCDE372 2 ACS/WFC ACCUM WFC1-CTE F850LP 2 none none none 1 610 S 16882( 4) - 07-Jan-2022 21:40:31 - [ 9] Visit: 05 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 UCDE374 ACS/WFC ACCUM WFC1-CTE F475W 1 800 S PATTERN 1 1-2 see below (770 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 UCDE374 ACS/WFC ACCUM WFC1-CTE F850LP 1 1280 S see below (1220 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 | ------------------------------------------------------------------------------------------------------------------------------------ UCDE374 1 ACS/WFC ACCUM WFC1-CTE F475W 1 none none none 1 385 S UCDE374 1 ACS/WFC ACCUM WFC1-CTE F475W 2 none none none 1 385 S UCDE374 2 ACS/WFC ACCUM WFC1-CTE F850LP 1 none none none 1 610 S UCDE374 2 ACS/WFC ACCUM WFC1-CTE F850LP 2 none none none 1 610 S 16882( 4) - 07-Jan-2022 21:40:31 - [ 10] Summary Form for Proposal 16882 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC, WFC1-CTE ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 1-2 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F475W, F850LP ------------------------------------------------------------------------------------------------------------------------------------ Target Names UCD218, UCD736, UCD761-OFFSET, UCDE372, UCDE374 ------------------------------------------------------------------------------------------------------------------------------------