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What a Tangled Web We Weave: Hermus as the Northern Extension of the Phoenix Stream

Grillmair, Carl J. and Carlberg, Raymond G. (2016) What a Tangled Web We Weave: Hermus as the Northern Extension of the Phoenix Stream. Astrophysical Journal Letters, 820 (2). Art. No. L27. ISSN 2041-8205.

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We investigate whether the recently discovered Phoenix stream may be part of a much longer stream that includes the previously discovered Hermus stream. Using a simple model of the Galaxy with a disk, bulge, and a spherical dark matter halo, we show that a nearly circular orbit, highly inclined with respect to the disk, can be found that fits the positions, orientations, and distances of both streams. While the two streams are somewhat misaligned in the sense that they do not occupy the same plane, nodal precession due to the Milky Way disk potential naturally brings the orbit into line with each stream in the course of half an orbit. We consequently consider a common origin for the two streams as plausible. Based on our best-fitting orbit, we make predictions for the positions, distances, radial velocities, and proper motions along each stream. If our hypothesis is borne out by measurements, then at ≈183° (≈235° with respect to the Galactic center) and ≈76 kpc in length, Phoenix–Hermus would become the longest cold stream yet found. This would make it a particularly valuable new probe of the shape and mass of the Galactic halo out to ≈20 kpc.

Item Type:Article
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URLURL TypeDescription Paper
Grillmair, Carl J.0000-0003-4072-169X
Additional Information:© 2016 The American Astronomical Society. Received 2016 February 15; accepted 2016 March 5; published 2016 March 23. We thank an anonymous referee for several useful suggestions that improved both the clarity and thoroughness of the manuscript.
Group:Infrared Processing and Analysis Center (IPAC)
Subject Keywords:Galaxy: halo; Galaxy: structure
Issue or Number:2
Record Number:CaltechAUTHORS:20160426-144224494
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Official Citation:Carl J. Grillmair and Raymond G. Carlberg 2016 ApJ 820 L27
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:66488
Deposited By: Ruth Sustaita
Deposited On:26 Apr 2016 22:27
Last Modified:03 Oct 2019 09:57

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