A Two Micron All-Sky Survey View of the Sagittarius Dwarf Galaxy. IV. Modeling the Sagittarius Tidal Tails

By D. Law, K. Johnston, S. Majewski. 2004

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M giants recovered from the Two Micron All-Sky Survey have recently been used to map the position and velocity distributions of tidal debris from the Sagittarius (Sgr) dwarf spheroidal galaxy around the entire Galaxy. We compare this data set to both test-particle orbits and N-body simulations of satellite destruction run within a variety of rigid Milky Way potentials, and we find that the mass of the Milky Way within 50 kpc of its center should be × 1011 M☉ in order for any Sgr orbit to simultaneously fit the velocity gradient in the Sgr trailing debris and the apocenter of the Sgr leading debris. Orbital pole precession of young debris and leading debris velocities in regions corresponding to older debris provide contradictory evidence in favor of oblate/prolate Galactic halo potentials, respectively, leading us to conclude that the orbit of Sgr has evolved over the past few gigayears. In light of this discrepancy, we consider constraints from only the younger portions of the debris within three models of the flattening of the Galactic potential [q = 0.90 (O), 1.0 (S), and 1.25 (P), i.e., oblate, spherical, and prolate] in our further N-body simulations. On the basis of the velocity dispersion and width along the trailing tidal stream, we estimate the current bound mass of Sgr to be MSgr = × 108 M☉ independent of the form of the Galactic potential; this corresponds to a range of mass-to-light ratios (M/L)Sgr = 14-36(M/L)☉ for the Sgr core. Models with masses in this range best fit the apocenter of leading Sgr tidal debris when they orbit with a radial period of roughly 0.85 Gyr and have perigalactica and apogalactica of about 15 and 60 kpc, respectively. These distances scale with the assumed distance to the Sgr dwarf and the assumed depth of the Galactic potential. The density distribution of debris along the orbit in these models is consistent with the M giant observations, and debris at all orbital phases in which M giants are obviously present is younger (i.e., was lost more recently from the satellite) than the typical age of a Sgr M giant star.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/f81feb98072f096017e18f39d713e57de92b41e9

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Citations in the corpus

Galactic Searches for Dark Matter (2012, background): “Modeling indicates that the dark matter mass of Sagittarius before it fell into the Milky Way halo was in the range 108− 109 M (Law et al., 2005).”
THE LEAST-LUMINOUS GALAXY: SPECTROSCOPY OF THE MILKY WAY SATELLITE SEGUE 1 (2008, methodology): “We refer the reader to Law et al. (2005) for a more thorough discussion of the N-body modeling technique.”
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): “…time to undergo differential procession, thereby severely weakening the constraints on the halo ellipticity (Helmi 2004a,b); current models are unable to simultaneously fit the velocities of stars in the leading stream and the orbital planes of the leading and trailing streams (Law et al. 2005).”
The ACS Survey of Galactic Globular Clusters: M54 and Young Populations in the Sagittarius Dwarf Spheroidal Galaxy (2007, background): “Because Sgr has been disrupting for at least 2.5–3.0 Gyr (Law et al. 2005) and likely longer, it is a unique laboratory for exploring star formation in the context of hierarchical galaxy formation.”
Precession of the Sagittarius stream (2013, result): “Wherever the datasets overlap, the leading tail kinematics reported here are in good agreement with the velocities of the Mgiants reported by Law et al. (2004, 2005).”
ON THE SHOULDERS OF GIANTS: PROPERTIES OF THE STELLAR HALO AND THE MILKY WAY MASS DISTRIBUTION (2014, methodology): “…orbital evolution ofthe satellite galaxies and globular clusters (Lin & Lynden-Bell 1982; Boylan-Kolchin et al. 2013), modeling the tidal streams (Law et al. 2005; Newberg et al. 2010; Sanders & Binney 2013b; Sanderson & Helmi 2013), the HI gas rotation curve (e.g. Sofue et al. 2009), fitting a…”
THE LUMINOSITY PROFILE AND STRUCTURAL PARAMETERS OF THE ANDROMEDA GALAXY (2011, background): “This number grows to 2% if unbound Sagittarius stream stars are included (Law et al. 2005).”
ASSESSING THE MILKY WAY SATELLITES ASSOCIATED WITH THE SAGITTARIUS DWARF SPHEROIDAL GALAXY (2010, background): “…observational data on the angular positions (e.g., Majewski et al. 2003; Belokurov et al. 2006a; Yanny et al. 2009), radial velocities (e.g., Law et al. 2004, 2005; Majewski et al. 2004; Monaco et al. 2007; Yanny et al. 2009), and chemical abundances (Chou et al. 2007, 2010; Monaco et al.…”
Extragalactic Globular Clusters and Galaxy Formation (2006, background): “Fornax and Sgr have total masses of >∼ 10 8M⊙ (Walcher et al. 2003; Law et al. 2005) and the total mass estimate for And I, assuming it has a similar M/L ratio, is a few ×107M⊙.”
Shredded Galaxies as the Source of Diffuse Intrahalo Light on Varying Scales (2007, background): “This number can be as large as fIHL 2% if the unbound Sagittarius stream stars are included in the diffuse component (e.g., Law et al. 2005).”
The importance of tides for the Local Group dwarf spheroidals (2005, methodology): “We used a host galaxy potential chosen to provide a good fit to the Milky Way (Law et al. 2005), with a Miyamoto-Nagai potential for the Milky Way disc and bulge (Nagai & Miyamoto 1976), and a logarithmic potential for the Milky Way dark matter halo.”
Tracing Galaxy Formation with Stellar Halos. II. Relating Substructure in Phase and Abundance Space to Accretion Histories (2008, background): “Numerous previous studies have looked at how to understand individual debris features around galaxies in terms of the properties of the progenitor dwarfs (e.g. Johnston 1998; Helmi & White 1999; Johnston, Sackett, & Bullock 2001; Law et al. 2005; Fardal et al. 2006; Warnick et al. 2008).”