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Published March 10, 2013 | Published
Journal Article Open

Evidence for a Milky Way Tidal Stream Reaching Beyond 100 kpc


We present the analysis of 1207 RR Lyrae found in photometry taken by the Catalina Survey's Mount Lemmon telescope. By combining accurate distances for these stars with measurements for ~14,000 type-ab RR Lyrae from the Catalina Schmidt telescope, we reveal an extended association that reaches Galactocentric distances beyond 100 kpc and overlaps the Sagittarius stream system. This result confirms earlier evidence for the existence of an outer halo tidal stream resulting from a disrupted stellar system. By comparing the RR Lyrae source density with that expected based on halo models, we find the detection has ~8σ significance. We investigate the distances, radial velocities, metallicities, and period-amplitude distribution of the RR Lyrae. We find that both radial velocities and distances are inconsistent with current models of the Sagittarius stream. We also find tentative evidence for a division in source metallicities for the most distant sources. Following prior analyses, we compare the locations and distances of the RR Lyrae with photometrically selected candidate horizontal branch stars and find supporting evidence that this structure spans at least 60° of the sky. We investigate the prospects of an association between the stream and the unusual globular cluster NGC 2419.

Additional Information

© 2013 American Astronomical Society. Received 2012 September 3; accepted 2013 January 24; published 2013 February 27. CRTS and CSDR1 are supported by the U.S. National Science Foundation under grants AST-0909182 and CNS-0540369. The CSS survey is funded by the National Aeronautics and Space Administration under Grant No. NNG05GF22G issued through the Science Mission Directorate Near-Earth Objects Observations Program. J.L.P. acknowledges support from NASA through Hubble Fellowship Grant HF-51261.01-A awarded by the STScI, which is operated by AURA, Inc., for NASA, under contract NAS 5-26555. Support for M.C. and G.T. is provided by the Ministry for the Economy, Development, and Tourism's Programa Inicativa Científica Milenio through grant P07-021-F, awarded to The Milky Way Millennium Nucleus; by Proyecto Basal PFB- 06/2007; by Proyecto FONDECYT Regular 1110326; and by Proyecto Anillo ACT-86. SDSS-III is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS-III Collaboration. Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy Office of Science. The SDSS-III Web site is http://www.sdss3.org/.

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