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Piercing the Milky Way: an all-sky view of the Orphan Stream

Koposov, S. E. and Belokurov, V. and Li, T. S. and Mateu, C. and Erkal, D. and Grillmair, C. J. and Hendel, D. and Price-Whelan, A. M. and Laporte, C. F. P. and Hawkins, K. and Sohn, S. T. and del Pino, A. and Evans, N. W. and Slater, C. T. and Kallivayalil, N. and Navarro, J. F. (2019) Piercing the Milky Way: an all-sky view of the Orphan Stream. Monthly Notices of the Royal Astronomical Society, 485 (4). pp. 4726-4742. ISSN 0035-8711. doi:10.1093/mnras/stz457.

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We use astrometry, broad-band photometry, and variability information from the Data Release 2 of ESA’s Gaia mission (GDR2) to identify members of the Orphan Stream (OS) across the whole sky. The stream is traced above and below the celestial equator and in both Galactic hemispheres, thus increasing its visible length to ∼210° equivalent to ∼150 kpc in physical extent. Taking advantage of the large number of RR Lyrae stars in the OS, we extract accurate distances and proper motions across the entire stretch of the tidal debris studied. As delineated by the GDR2 RR Lyrae, the stream exhibits two prominent twists in its shape on the sky which are accompanied by changes in the tangential motion. We complement the RR Lyrae maps with those created using GDR2 Red Giants and the DECam Legacy Survey Main Sequence Turn-Off stars. The behaviour of the OS track on the sky is consistent across all three tracers employed. We detect a strong non-zero motion in the across-stream direction for a substantial portion of the stream. Such a misalignment between the debris track and the streaming velocity cannot be reproduced in a static gravitational potential and signals an interaction with a massive perturber.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Koposov, S. E.0000-0003-2644-135X
Belokurov, V.0000-0002-0038-9584
Mateu, C.0000-0002-6330-2394
Erkal, D.0000-0002-8448-5505
Grillmair, C. J.0000-0003-4072-169X
Hendel, D.0000-0002-7939-7607
Price-Whelan, A. M.0000-0003-0872-7098
Laporte, C. F. P.0000-0003-3922-7336
Hawkins, K.0000-0002-1423-2174
Additional Information:© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2019 February 11. Received 2019 February 10; in original form 2018 December 20. This work was performed at the Aspen Center for Physics, which is supported by National Science Foundation grant PHY-1607611. We thank Michael for an illuminating discussion. The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC grant agreement no. 308024. SK is partially supported by NSF grant AST-1813881. NK is supported by NSF CAREER award 1455260. This work presents results from the European Space Agency (ESA) space mission Gaia. Gaia data are being processed by the Gaia Data Processing and Analysis Consortium (DPAC). Funding for the DPAC is provided by national institutions, in particular the institutions participating in the Gaia MultiLateral Agreement. The Gaia mission website is The Gaia archive website is This project used public archival data from the DES. Funding for the DES Projects has been provided by the U.S. Department of Energy, the U.S. National Science Foundation, the Ministry of Science and Education of Spain, the Science and Technology Facilities Council of the United Kingdom, the Higher Education Funding Council for England, the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, the Kavli Institute of Cosmological Physics at the University of Chicago, the Center for Cosmology and Astro-Particle Physics at the Ohio State University, the Mitchell Institute for Fundamental Physics and Astronomy at Texas A&M University, Financiadora de Estudos e Projetos, Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, Conselho Nacional de Desenvolvimento Científico e Tecnológico and the Ministério da Ciência, Tecnologia e Inovação, the Deutsche Forschungsgemeinschaft, and the Collaborating Institutions in the DES. The Collaborating Institutions are Argonne National Laboratory, the University of California at Santa Cruz, the University of Cambridge, Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas-Madrid, the University of Chicago, University College London, the DES-Brazil Consortium, the University of Edinburgh, the Eidgenössische Technische Hochschule (ETH) Zürich, Fermi National Accelerator Laboratory, the University of Illinois at Urbana-Champaign, the Institut de Ciències de l’Espai (IEEC/CSIC), the Institut de Física d’Altes Energies, Lawrence Berkeley National Laboratory, the Ludwig-Maximilians Universität München and the associated Excellence Cluster Universe, the University of Michigan, the National Optical Astronomy Observatory, the University of Nottingham, The Ohio State University, the OzDES Membership Consortium, the University of Pennsylvania, the University of Portsmouth, SLAC National Accelerator Laboratory, Stanford University, the University of Sussex, and Texas A&M University. Based in part on observations at Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. The Legacy Surveys consist of three individual and complementary projects: the DECaLS (NOAO Proposal ID no. 2014B-0404; PIs: David Schlegel and Arjun Dey), the Beijing-Arizona Sky Survey (BASS; NOAO Proposal ID no. 2015A-0801; PIs: Zhou Xu and Xiaohui Fan), and the Mayall z-band Legacy Survey (MzLS; NOAO Proposal ID no. 2016A-0453; PI: Arjun Dey). DECaLS, BASS, and MzLS together include data obtained, respectively, at the Blanco telescope, Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory (NOAO); the Bok telescope, Steward Observatory, University of Arizona; and the Mayall telescope, Kitt Peak National Observatory, NOAO. The Legacy Surveys project is honored to be permitted to conduct astronomical research on Iolkam Du’ag (Kitt Peak), a mountain with particular significance to the Tohono O’odham Nation. NOAO is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. The Legacy Survey team makes use of data products from the Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE), which is a project of the Jet Propulsion Laboratory/California Institute of Technology. NEOWISE is funded by the National Aeronautics and Space Administration. The Legacy Surveys imaging of the DESI footprint is supported by the Director, Office of Science, Office of High Energy Physics of the U.S. Department of Energy under Contract No. DE-AC02-05CH1123, by the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility under the same contract; and by the U.S. National Science Foundation, Division of Astronomical Sciences under contract no. AST-0950945 to NOAO.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
European Research Council (ERC)308024
Gaia Multilateral AgreementUNSPECIFIED
Department of Energy (DOE)DE-AC02-05CH1123
Canadian Institute for Advanced Research (CIFAR)UNSPECIFIED
Subject Keywords:Galaxy: halo, Galaxy: kinematics and dynamics, Galaxy: structure, galaxies: dwarf, galaxies: structure
Issue or Number:4
Record Number:CaltechAUTHORS:20190725-125943511
Persistent URL:
Official Citation:S E Koposov, V Belokurov, T S Li, C Mateu, D Erkal, C J Grillmair, D Hendel, A M Price-Whelan, C F P Laporte, K Hawkins, S T Sohn, A del Pino, N W Evans, C T Slater, N Kallivayalil, J F Navarro, Piercing the Milky Way: an all-sky view of the Orphan Stream, Monthly Notices of the Royal Astronomical Society, Volume 485, Issue 4, June 2019, Pages 4726–4742,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:97409
Deposited By: George Porter
Deposited On:25 Jul 2019 23:12
Last Modified:16 Nov 2021 17:31

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