Third submission, typos fixed 1435315242 Assigned ID: 5975 ----- Attempting Submission 1 (Thu Nov 07 13:30:38 GMT 2024) ----- HST Phase I Proposal 5975 successfully submitted. Receipt: # 5975-1 ----- Attempting Submission 2 (Thu Nov 07 23:08:34 GMT 2024) ----- HST Phase I Proposal 5975 successfully submitted. Receipt: # 5975-2 ----- Attempting Submission 3 (Fri Nov 08 00:39:01 GMT 2024) ----- Phase for GO-17925. Cen A observations for proper motions. 1168028899 ----- Attempting Submission 1 (Wed Jan 29 19:19:44 GMT 2025) ----- 20 Years of time baseline, The 3D kinematics of Centaurus A Centaurus A (Cen A, NGC 5128) is the nearest elliptical galaxy to the Milky Way (MW), the most massive galaxy in the Local Volume and the nearest galaxy to host an active galactic nucleus (AGN). Cen A's importance to astronomy is exemplified by it being one of the 20 most cited objects in the SIMBAD database. We propose to use ACS/WFC to measure the proper motion (PM) of Cen A and use this information to: (1) for the first time, measure the transverse velocity of a galaxy group relative to the Local Group (LG), allowing us totest cosmological expectations and simulations in a new way and on far larger scales, and, (2) begin the process of determining the long-term stability of the reported plane of satellites in the Cen A group. It is vital that the second epoch of observations needed to derive Cen~A's PM is taken before ACS/WFC is decommissioned. Second-epoch observations with any other instrument would produce PMs with significant systematics, and new observations would need over 20 years to achieve the precision possible now with ACS/WFC. We will observe a halo field for Cen A with 12 single orbit exposures. This will allow us to get a second epoch of observations for finding the proper motion of Cen A and its galaxy group. Team Expertise: 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). Dr Bennet has also succesfully led multiple HST programs related to the photometry and astrometry of galaxies using ACS (e.g. GO-15858, GO-17174 and GO-17501). Dr Bennet will lead and 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. Dr Sohn will contribute to the PM measurements part of this work. Co-I Dr Ekta Patel is an expert in orbital modelling and mass modelling in the Local Group. Dr Patel will contribute to the orbital history of our target based on the PMs found in this program. Co-I, Dr K. McKinnon is an expert in rigorous statistical combinations of HST images with Gaia data, which enables significantly improved measurements of astrometry than either dataset can measure alone. Co-I Dr. Marcel Pawlowski is an expert on satellite planes and on testing cosmological expectations with the dynamics of galaxies and will assist in the interpretation of these results in that context. Co-Is Dr Mark Fardal, Dr Roeland van der Marel, Dr Nitya Kallivayalil, Dr Laura Watkins and Mr Jack Warfield 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 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 SUPPORTED GALAXY ELLIPTICAL HALO YES This is the magnitude of a TRGB star, at this distance Cen A is resolved into indivdual stars and we are well into the halo so the magnitude of Cen A itself is irrelevent to these observations. J2000 J2000 ACS/WFC Imaging No No F814W /private/var/folders/w_/jnjpw_kd2_dgbfb8dt29vldc0002m5/T/OPVisit7649596204441054315.xml Timing link suitability includes constraints ([Group (01 02 03 04 05 06) Within 30.0 days]) Hst Same orient constraint links visits (01 02 03 04 05 06) The scheduling data was generated by CASM 33.0. CASM was run in Phase II mode. 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