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Joint Survey Processing II: Stellar Proper Motions in the COSMOS Field from Hubble Space Telescope ACS and Subaru Telescope HSC Observations

Presentation #407.08 in the session The Milky Way, the Galactic Center — iPoster Session.

Published onJun 29, 2022
Joint Survey Processing II: Stellar Proper Motions in the COSMOS Field from Hubble Space Telescope ACS and Subaru Telescope HSC Observations

We analyze stellar proper motions in the COSMOS field to assess the presence of bulk motions. At bright magnitudes (G band 18.5–20.7 AB), we use the proper motions of stars in the Gaia DR2 catalog. At the faint end, we computed proper motions of nearly 12,000 stars at i band magnitudes 19–25 AB using Hubble ACS and Subaru HSC. In order to measure these proper motions with unprecedented accuracy at faint magnitudes, we developed a foundational set of astrometric tools which will be required for Joint Survey Processing (JSP) of data from the next generation of optical/infrared surveys. The astrometric grids of Hubble ACS and Subaru HSC mosaics were corrected at the catalog level, using proper motion-propagated and parallax-corrected Gaia DR2 sources. Upon comparison of our measured proper motions with Gaia DR2, we estimate the uncertainties in our measurements to be 2–3 mas/yr per axis, down to 25.5 AB mag. These uncertainties are a factor of about 2.5 better than those from simple catalog matching if no proper motions of Gaia sources are taken into account. We calculated galactic space velocities of late-type main-sequence stars in the thin and thick disks in the COSMOS field. We also detected candidate high-velocity (220 km/s) giant stars, five of them at 20 kpc distance, that may be Galactic halo members of the Sangarius stream.

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