S316p.72 — The Tidal Radius of the Arches Cluster

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Aug 10th at 6:00 PM until 7:30 PM

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Author(s): Matthew Hosek2, Jessica R Lu2, Jay Anderson1, Andrea Ghez3, Mark Morris3, William Clarkson4

Institution(s): 1. Space Telescope Science Institute, 2. University of Hawaii at Manoa, 3. University of Los Angeles , 4. University of Michigan-Dearborn

At a projected distance of just ∼26 pc from the center of the Milky Way, the Arches cluster allows us to examine the structure of a young massive cluster in the strong tidal environment of the Galactic center (GC). We use the HST WFC3IR camera to conduct an astrometric and photometric study of the outer region of the Arches cluster (R > 6.25”) in order to measure its radial profile. Using proper motions we separate cluster members from field stars down to F153M = 20 mag (∼2.5 M_sun) over a 120” x 120” field of view, covering an area 144 times larger than previous proper motion studies. This is a significant improvement over photometrically-determined cluster membership, which is complicated by the high degree of differential reddening across the field. Using cluster membership probabilities, a derived extinction map, and extensive completeness simulations, we construct the radial profile of the Arches cluster to a radius of ∼80” (∼3.1 pc assuming a distance of 8 kpc). Evidence of mass segregation out to this radius is observed, and no significant tidal tail structure is apparent. We find that the projected radial extent of the Arches cluster is significantly larger than its expected tidal radius. This result suggests either that the cluster is not as close to the GC as previously thought or that it is inflated beyond its nominal tidal radius.