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The total mass of the Large Magellanic Cloud from its perturbation on the Orphan stream

Erkal, D. and Belokurov, V. and Laporte, C. F. P. and Koposov, S. E. and Li, T. S. and Grillmair, C. J. and Kallivayalil, N. and Price-Whelan, A. M. and Evans, N. W. and Hawkins, K. and Hendel, D. and Mateu, C. and Navarro, J. F. and del Pino, A. and Slater, C. T. and Sohn, S. T. (2019) The total mass of the Large Magellanic Cloud from its perturbation on the Orphan stream. Monthly Notices of the Royal Astronomical Society, 487 (2). pp. 2685-2700. ISSN 0035-8711. doi:10.1093/mnras/stz1371.

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In a companion paper by Koposov et al., RR Lyrae from Gaia Data Release 2 are used to demonstrate that stars in the Orphan stream have velocity vectors significantly misaligned with the stream track, suggesting that it has received a large gravitational perturbation from a satellite of the Milky Way. We argue that such a mismatch cannot arise due to any realistic static Milky Way potential and then explore the perturbative effects of the Large Magellanic Cloud (LMC). We find that the LMC can produce precisely, the observed motion-track mismatch and we therefore use the Orphan stream to measure the mass of the Cloud. We simultaneously fit the Milky Way and LMC potentials and infer that a total LMC mass of 1.38^(+0.27)_(−0.24) × 10^(11) M_⊙ is required to bend the Orphan stream, showing for the first time that the LMC has a large and measurable effect on structures orbiting the Milky Way. This has far-reaching consequences for any technique which assumes that tracers are orbiting a static Milky Way. Furthermore, we measure the Milky Way mass within 50 kpc to be 3.80^(+0.14)_(−0.11) × 10^(11) M_⊙⁠. Finally, we use these results to predict that, due to the reflex motion of the Milky Way in response to the LMC, the outskirts of the Milky Way’s stellar halo should exhibit a bulk, upwards motion.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Erkal, D.0000-0002-8448-5505
Belokurov, V.0000-0002-0038-9584
Laporte, C. F. P.0000-0003-3922-7336
Koposov, S. E.0000-0003-2644-135X
Grillmair, C. J.0000-0003-4072-169X
Price-Whelan, A. M.0000-0003-0872-7098
Hawkins, K.0000-0002-1423-2174
Hendel, D.0000-0002-7939-7607
Mateu, C.0000-0002-6330-2394
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 May 10. Received 2019 May 9; in original form 2018 December 20. We thank the streams group at Cambridge and Eugene Vasiliev for helpful comments which improved the clarity of this work. DE thanks Michelle Collins and Shu Kim for insightful discussions. We thank the anonymous referee for their thoughtful comments which have improved the clarity of this work. This work was started 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 number 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 (MLA). The Gaia mission website is The Gaia archive website is This research made use of IPYTHON (Perez & Granger 2007), PYTHON packages NUMPY (van der Walt, Colbert & Varoquaux 2011), MATPLOTLIB (Hunter 2007), and SCIPY (Jones et al. 2001). This research also made use of Astropy,1 a community-developed core PYTHON package for Astronomy (Astropy Collaboration et al. 2013; Price-Whelan et al. 2018).
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
European Research Council (ERC)308024
Gaia Multilateral AgreementUNSPECIFIED
Subject Keywords:Galaxy: evolution, Galaxy: halo, Galaxy: kinematics and dynamics, Galaxy: structure, Magellanic Clouds
Issue or Number:2
Record Number:CaltechAUTHORS:20190725-125944640
Persistent URL:
Official Citation:D Erkal, V Belokurov, C F P Laporte, S E Koposov, T S Li, C J Grillmair, N Kallivayalil, A M Price-Whelan, N W Evans, K Hawkins, D Hendel, C Mateu, J F Navarro, A del Pino, C T Slater, S T Sohn, (The OATs: Orphan Aspen Treasury Collaboration), The total mass of the Large Magellanic Cloud from its perturbation on the Orphan stream, Monthly Notices of the Royal Astronomical Society, Volume 487, Issue 2, August 2019, Pages 2685–2700,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:97417
Deposited By: George Porter
Deposited On:25 Jul 2019 21:31
Last Modified:16 Nov 2021 17:31

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