High-resolution ACS/WFC Imaging of Compact Stellar Systems in the Virgo Cluster in Support of JWST Cycle 1 Science

0 Assigned ID: 2594 ----- Attempting Submission 1 (Thu Sep 30 17:10:50 GMT 2021) ----- HST Phase I Proposal 2594 successfully submitted. Receipt: # 2594-1 This target is not used in this proposal. This target is not used in this proposal. There are two errors thrown up for targets UCD761 and the associated "-OFFSETSTAR". Our science target is UCD761, but we would like to include the dwarf galaxy to the North as an ancillary science target. I've set up "UCD761-OFFSET" to acquire on "-OFFSETSTAR" before offsetting to the final coordinates. -comment still applies 01/07/2022 -1727965578 ----- Attempting Submission 1 (Tue Nov 30 21:53:44 GMT 2021) ----- HST Phase II Proposal 16882 successfully submitted. Receipt: # 16882-1 ----- Attempting Submission 2 (Tue Dec 07 22:19:36 GMT 2021) ----- ----- Attempting Submission 3 (Fri Jan 07 21:28:38 GMT 2022) ----- There are two warnings about targets not being used. Target UCD761 is the science target with its proper coordinates. UCD761-OFFSETSTAR is meant to be the acquisition target, and UCD761-OFFSET is where the data is to be taken. The offset is meant to include a nearby dwarf galaxy to the North in the instrument FoV. High-resolution ACS/WFC Imaging of Compact Stellar Systems in the Virgo Cluster in Support of JWST Cycle 1 Science 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. 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 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. We have compiled an international team from observational and theoretical backgrounds that address the topics and challenges covered by this program. We list a brief summary of the expertise of key team members as follows. Drs. Cote, Ko, Liu, Peng, Roediger, Taylor, and Wang are experts on low-mass dwarf galaxies and compact stellar systems (CSSs), including the stellar populations, formation and evolution, and internal kinematics of individual systems, as well as their global characteristics in the context of large-scale populations that comprise ths satellite systems of galaxy groups and clusters. Drs. Ferrarese, Valluri, and Vasiliev are authorities on the formation, growth, and characterization of massive black holes over cosmic time, with expertise ranging from fundamental scaling relations between BHs and their host galaxies, to their observational signatures and in constructing dynamical models of their influence on CSSs using state-of-the-art Jeans and Schwarzschild codes. Together, our team provides ample exptertise and experience to extract our science goals from this modest HST Midcycle program rapidly, with the ultimate goal of maximizing the scientific return of the approved JWST Cycle 1 program that our proposed HST observations are meant to support. Supermassive Black Holes and Active Galaxies 3 false false false false false true false SUPPORTED EXT-CLUSTER GLOBULAR CLUSTER NUCLEUS NO 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. J2000 J2000 EXT-CLUSTER GLOBULAR CLUSTER NUCLEUS NO J2000 J2000 EXT-CLUSTER GLOBULAR CLUSTER NUCLEUS NO J2000 J2000 EXT-CLUSTER GLOBULAR CLUSTER NUCLEUS NO J2000 J2000 EXT-CLUSTER GLOBULAR CLUSTER NUCLEUS NO J2000 J2000 UNIDENTIFIED UNDESIGNATED NO J2000 STAR UNDESIGNATED NO 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. J2000 J2000 ACS/WFC Imaging No No F475W ACS/WFC Imaging No No F850LP ACS/WFC Imaging No No F555W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F555W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F555W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F555W ACS/WFC Imaging No No F814W POS-TARG DITHER 3.034 LINE false false 2 85.29 ACS-WFC-DITHER-LINE 1

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