Velocity Trends in the Debris of Sagittarius and the Shape of the Dark Matter Halo of Our Galaxy

By A. Helmi. 2004

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Recently, radial velocities have been measured for a large sample of M giants from the Two Micron All Sky Survey catalog, selected to be part of the Sgr dwarf leading and trailing streams. Here we present a comparison of their kinematics to models of the Sgr dwarf debris orbiting Galactic potentials, with halo components of varying degrees of flattening and elongation. This comparison shows that the portion of the trailing stream mapped so far is dynamically young and hence does not provide very stringent constraints on the shape of the Galactic dark matter halo. The leading stream, however, contains slightly older debris, and its kinematics provide for the first time direct evidence that the dark matter halo of our Galaxy has a prolate shape with an average density axis ratio within the orbit of Sgr close to 5/3.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/fb699efd8b327fe5239c21715e8f5fc0afa5a4f8

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Citations in the corpus

THE SAGITTARIUS DWARF GALAXY: A MODEL FOR EVOLUTION IN A TRIAXIAL MILKY WAY HALO (2010, background): “Depending on which criterion a given study chose to focus, claims have been made in favor of an oblate halo (e.g., Johnston et al. 2005; Mart́ınez-Delgado et al. 2007), an approximately spherical halo (e.g., Ibata et al. 2001b; Fellhauer et al. 2006), and a prolate halo (e.g., Helmi 2004).”
Precession of the Sagittarius stream (2013, background): “…remains largely unstudied, yeta broadbrush picture of the wide and luminous Sgr stream is slowly taking shape, thanks to the diversity of the disruption models at hand (e.g. Ibata et al. 2001; Helmi 2004; Johnston et al. 2005; Fellhauer et al. 2006; Law & Majewski 2010; Peñarrubia et al. 2010).”
The local dark matter density (2014, background): “It would also essentially rule out weak field alternative gravity theories that require the gravitational potential to share symmetry properties with the disc (Helmi, 2004; Read & Moore, 2005).”
The shape of dark matter haloes : dependence on mass, redshift, radius and formation (2005, methodology): “Helmi (2004) claims that a study of the M giants in the leading edge of the stream tidally stripped from the Sagittarius dwarf galaxy leads to a best-fitting prolate halo with s = 0.6.”
Mass and shape of the Milky Way’s dark matter halo with globular clusters from Gaia and Hubble (2018, result): “…by tracers and methods is not straightforward, here we note that our estimate roughly agrees with others presented studying the Sagittarius stream (Helmi 2004), the flaring of the HI disc (Banerjee & Jog 2011) or the kinematics of halo stars (Bowden, Evans, & Williams 2016), while being…”
The distribution of satellite galaxies: the great pancake (2005, result): “This inference is consistent with the conclusion reached by Helmi (2004) from an analysis of the kinematics of the Sagittarius dwarf streams.”
KINEMATICAL AND CHEMICAL VERTICAL STRUCTURE OF THE GALACTIC THICK DISK. II. A LACK OF DARK MATTER IN THE SOLAR NEIGHBORHOOD, (2012, methodology): “…constraints on the DM halo shape are scarce and often controversial and, while spherical structures are usually preferred (e.g. Ibata et al. 2001; Majewski et al. 2003; Johnston et al. 2005; Fellhauer et al. 2006), a prolate spheroid (q = 5/3) was invoked by Helmi (2004) and Law et al. (2005).”
VERTICAL STRUCTURE OF A SUPERNOVA-DRIVEN TURBULENT, MAGNETIZED INTERSTELLAR MEDIUM (2012, background): “The shape of the dark halo of the Galaxy is unknown; claims of an oblate, spheroidal, and prolate halo have all been made (e.g., Helmi 2004; Johnston et al. 2005; Fellhauer et al. 2006; Law & Majewski 2010).”
The Masses of the Milky Way and Andromeda galaxies (2010, background): “This has told us that the halo is nearly spherical (Fellhauer et al. 2006), prolate (Helmi 2004), oblate (Johnston, Law & Majewski 2005) or triaxial (Law, Majewski & Johnston 2009) in nature!”
The total mass of the Large Magellanic Cloud from its perturbation on the Orphan stream (2018, background): “Moreover, streams are sensitive probes of the shape of the underlying potential (see Ibata et al. 2001; Helmi 2004; Johnston, Law & Majewski 2005; Fellhauer et al. 2006; Law & Majewski 2010; Bowden, Belokurov & Evans 2015) and their twisting and fanning can be used to understand the amount of…”
The Galaxy in Context: Structural, Kinematic, and Integrated Properties (2016, background): “The geometry of the stream on the sky has been shown to require an oblate near-spherical halo (Ibata et al. 2001, Johnston et al. 2005), whereas LOS velocities favor a prolate shape (Helmi 2004).”
Is the SMC Bound to the LMC? The Hubble Space Telescope Proper Motion of the SMC (2006, background): “…Magellanic Stream with tidal streams from other Local Group dwarfs, such as the Sagittarius Stream (Ibata et al. 1994; Majewski et al. 2003), might further constrain the potential of the halo (e.g., Fellhauer et al. 2006; Belokurov et al. 2006; Johnston et al. 2005; Law et al. 2005; Helmi 2004).”
Internal and External Alignment of the Shapes and Angular Momenta of ΛCDM Halos (2004, background): “Helmi (2004b) even claims that the stream is best fit assuming a prolate halo elongated perpendicular to the disk with c/a ≈ 0.6.”
A Two Micron All-Sky Survey View of the Sagittarius Dwarf Galaxy. IV. Modeling the Sagittarius Tidal Tails (2004, methodology): “Helmi (2004) has presented evidence in favor of a prolate (q ¼ 1:25) halo using Sgr leading debris velocity trends, while in a companion paper (Johnston et al. 2005, hereafter Paper III) we have demonstrated that such prolate halos fail to reproduce the observed orbital pole precession of leading…”
A Two Micron All Sky Survey View of the Sagittarius Dwarf Galaxy. III. Constraints on the Flattening of the Galactic Halo (2004, background): “In §3.1 we present a qualitative assessment of Aitoff projections of Sgr debris, and demonstrate similarly to previous discussions (e.g. Helmi 2004a) that such qualitative analyses provide little information on halo flattening.”
Equilibrium Disk-Bulge-Halo Models for the Milky Way and Andromeda Galaxies (2005, methodology): “…Sagittarius dwarf galaxy (see Majewski et al. 2003 and references therein) has intensified interest in performing simulations of the tidal dis- ruption of this system (Ibata et al. 1997; Helmi 2004; see also Geehan et al. 2005 for a study of the Andromeda stream in a disk-bulge-halo model of M31).”
The shape of dark matter haloes in the Aquarius simulations: evolution and memory (2011, methodology): “…was used to argue that the Milky Way halo is nearly spherical (Ibata et al. 2001; Mart́ınez-Delgado et al. 2004; Johnston et al. 2005) whereas the kinematics of stars in the leading stream could only be fit in a prolate halo elongated perpendicular to the disc (Helmi 2004; Law et al. 2005).”