The proper motion of the Arches cluster with Keck laser-guide star adaptive optics
Abstract
We present the first measurement of the proper motion of the young, compact Arches cluster near the Galactic center from near-infrared adaptive optics (AO) data taken with the recently commissioned laser-guide star (LGS) at the Keck 10 m telescope. The excellent astrometric accuracy achieved with LGS-AO provides the basis for a detailed comparison with VLT/NAOS-CONICA data taken 4.3 yr earlier. Over the 4.3 yr baseline, a spatial displacement of the Arches cluster with respect to the field population is measured to be 24.0 ± 2.2 mas, corresponding to a proper motion of 5.6 ± 0.5 mas yr^−1 or 212 ± 29 km s^−1 at a distance of 8 kpc. In combination with the known line-of-sight velocity of the cluster, we derive a three-dimensional (3D) space motion of 232 ± 30 km s^−1 of the Arches relative to the field. The large proper motion of the Arches cannot be explained with any of the closed orbital families observed in gas clouds in the bar potential of the inner Galaxy, but would be consistent with the Arches being on a transitional trajectory between x1 and x2 orbits. We investigate a cloud-cloud collision as the possible origin for the Arches cluster. The integration of the cluster orbit in the potential of the inner Galaxy suggests that the cluster passes within 10 pc of the supermassive black hole only if its true GC distance is very close to its projected distance. A contribution of young stars from the Arches cluster to the young stellar population in the inner few parsecs of the GC thus appears increasingly unlikely. The measurement of the 3D velocity and orbital analysis provides the first observational evidence that Arches-like clusters do not spiral into the GC. This confirms that no progenitor clusters to the nuclear cluster are observed at the present epoch.
Additional Information
© 2008 The American Astronomical Society. Received 2007 May 1; accepted 2007 November 10. The authors wish to thank the anonymous referee for thoughtful comments on the manuscript and in particular on the cluster formation scenarios. We thank Brad Hansen, Mike Rich, and Hong Sheng Zhao for insights on the dynamical properties in the inner Galaxy and orbital considerations, and Ralf Launhardt for kindly providing his enclosed mass measurements and density distributions, and acknowledge fruitful discussions with Mike Muno and Claire Max. W. B. acknowledges support by a Julian Schwinger Fellowship at UCLA. This work would not have been possible without the intense effort and dedication of the Keck LGS-AO staff. We are deeply grateful for their support enabling these observations. The W. M. Keck Observatory is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. This work was supported by NSF grant AST 04 06-816 and by the Science and Technology Center for Adaptive Optics, managed by the University of California at Santa Cruz under cooperative agreement AST 98 76-783.Attached Files
Published - STOapj08.pdf
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Additional details
- Eprint ID
- 14167
- Resolver ID
- CaltechAUTHORS:20090506-140155805
- AST 04 06-816
- NSF
- AST 98 76-783
- NSF
- Created
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2009-05-11Created from EPrint's datestamp field
- Updated
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2021-11-08Created from EPrint's last_modified field