New Kids on the Block? Proper Motions of First Infall Galaxies in the Local Group

0 Assigned ID: 3358 ----- Attempting Submission 1 (Fri Mar 25 17:34:50 GMT 2022) ----- HST Phase I Proposal 3358 successfully submitted. Receipt: # 3358-1 ----- Attempting Submission 2 (Fri Mar 25 20:38:10 GMT 2022) ----- HST Phase I Proposal 3358 successfully submitted. Receipt: # 3358-2 ----- Attempting Submission 3 (Fri Mar 25 22:33:07 GMT 2022) ----- Following a final check of the Phase II, as requested by the Program Coorindator, an error was found in the original Phase II submission. The error has now been corrected in this resubmission. 1593400141 ----- Attempting Submission 1 (Tue Jul 12 22:37:22 GMT 2022) ----- ----- Attempting Submission 2 (Fri Apr 28 16:57:06 GMT 2023) ----- New Kids on the Block? Proper Motions of First Infall Galaxies in the Local Group The Local Group (LG) is dominated by the Milky Way (MW), Andromeda (M31) and Triangulum (M33) galaxies. Their inner satellite systems have been well studied, but there are galaxies that live at the edges of these systems whose nature and histories are poorly understood. They trace a key part of the host's mass distribution not probed by closer-in satellites. We propose to measure proper motions (PMs) for 4 such LG dwarf galaxies: LeoT (MW satellite), Aquarius (M31), Pegasus (M31), and Pisces (M31 or M33?). Combining the new HST PMs with existing line-of-sight velocities, we will precisely determine their orbits, and compare the orbital characteristics and timescales with their existing SF histories. This will enable us to address several key questions. Are they bound or unbound to their putative hosts? Are they falling in to their hosts for the first time or have they fallen in before and splashed back again? Their infall is thought to trigger a burst of star formation (SF) and then quench, but on what timescales, and at what distance from the host do these events occur? What are the outer mass distributions of their hosts, and the mass of the LG as a whole? Is Pisces the first known satellite of M33? The target galaxies are too far and faint for Gaia to study. Only HST has the depth, astrometric precision and long time baselines via its Archive to measure these PMs. With Hubble's exceptional longevity and stability, we are able to continue to push back the frontiers of LG science. The main goal of this program is to measure absolute proper motions of the four target galaxies PIisces-1, Aquarius, Pegasus, and Leo T dwarf galaxies. For this, we will use compact background galaxies in the field view as stationary reference sources. The target galaxies have already been observed either in one or two separate epochs. The imaging data from this program will add another epoch thereby yielding a time baseline in the rage 10-17 years. For the proper motion measurements, we will measure the average motion of stars in each dwarf galaxy with respect to compact background galaxies using the multi-epoch data. Our analysis techniques and expected accuracies are described in the Phase I proposal. The first epoch ACS/WFC data were obtained in at least two filters to make deep color magnitude diagrams for the target galaxies. The available broad-band colors and depth are sufficient for separating stars, foreground stars, and background galaxies to first order. For the current program, we will observe each target galaxy with the F814W filter, except for Leo T which will be observed in F606W, using the same pointing and orientation used for the first-epoch data. We therefore added Visit Orient Requirements to all visits. Individual exposures will be sub-pixel dithered using custom-designed dithering pattern through POSTARG requirement to maximize pixel-phase coverage, and will last half an orbit. We request each target galaxy to be observed in two visits with 5 orbits (for Aquarius dwarf) or 3 orbits (all other targets) each. For the two separate visits for each target, we added Timinig Requirements "GROUP WITHIN 30D" so that they can be treated as single epoch data for astrometric analyses. All investigators are members of the HSTPROMO group, led by co-I van der Marel, which has published numerous papers reporting proper motion measurements of dwarf galaxies, globular clusters, individual stars along stellar streams, and distant Milky Way (MW) halo stars. PI Dr Paul Bennet is an expert in satellites inside and outside of the LG. He has had previous experience leading successful HST programs e.g GO-15858 (Bennet et al. 2020). He will perform the majority of the work for this project. Co-I Dr Tony Sohn is an expert in measuring HST proper motions, his past measurements include M31, bulk proper motions of dwarf spheroidal galaxies in the Milky Way halo (Leo I, Draco, and Sculptor), individual proper motions of stars along stellar streams such as Sagittarius, Orphan, and Lethe, distant Milky Way globular clusters, and M31 satellites NGC 147 and 185. He will contribute to the PM measurements part of this work. Co-I Dr Andres del Pino-Molina is an expert in analysis of internal dynamics and star formation histories of dwarf galaxies in the Local Group. He will contribute to the interpretation of the results. Co-Is Dr Mark Fardal, Dr Ekta Patel, Dr Roeland van der Marel, and Dr Laura Watkins are experts in HST kinematic analysis, dynamical mass estimation, and dynamical modeling of Local Group galaxies including both equilibrium and N-body modeling. They will contribute to the orbital calculations and interpretation of the results. See list of refereed publications by the HSTPROMO group at http://www.stsci.edu/~marel/hstpromo.html#Papers Stellar Populations and the Interstellar Medium Galaxies 6 false false false false false false false false SUPPORTED GALAXY DWARF ELLIPTICAL DWARF SPHEROIDAL J2000 J2000 GALAXY DWARF ELLIPTICAL DWARF SPHEROIDAL This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 GALAXY DWARF ELLIPTICAL DWARF SPHEROIDAL This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 GALAXY DWARF ELLIPTICAL DWARF SPHEROIDAL This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F606W 1682697946754 Timing link suitability includes constraints ([Group (01 02) Within 30.0 days]) The scheduling data was generated by CASM 31.0. 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