THE SAGITTARIUS DWARF GALAXY: A MODEL FOR EVOLUTION IN A TRIAXIAL MILKY WAY HALO

By D. Law, S. Majewski. 2010

346 citations recorded by the source corpus.

We present a new N-body model for the tidal disruption of the Sagittarius (Sgr) dwarf that is capable of simultaneously satisfying the majority of angular position, distance, and radial velocity constraints imposed by current wide-field surveys of its dynamically young (≲3 Gyr) tidal debris streams. In particular, this model resolves the conflicting angular position and radial velocity constraints on the Sgr leading tidal stream that have been highlighted in recent years. While the model does not reproduce the apparent bifurcation observed in the leading debris stream, recent observational data suggest that this bifurcation may represent a constraint on the internal properties of the Sgr dwarf rather than the details of its orbit. The key element in the success of this model is the introduction of a non-axisymmetric component to the Galactic gravitational potential that can be described in terms of a triaxial dark matter halo whose minor/major axis ratio (c/a)Φ = 0.72 and intermediate/major axis ratio (b/a)Φ = 0.99 at radii 20 kpc < r < 60 kpc. The minor/intermediate/major axes of this halo lie along the directions (l, b) = (7°, 0°), (0°, 90°), and (97°, 0°) respectively, corresponding to a nearly oblate ellipsoid whose minor axis is contained within the Galactic disk plane. This particular disk/halo orientation is difficult to reconcile within the general context of galactic dynamics (and cold dark matter models in particular), suggesting either that the orientation may have evolved significantly with time or that inclusion of other non-axisymmetric components (such as the gravitational influence of the Magellanic Clouds) in the model may obviate the need for triaxiality in the dark matter halo. The apparent proper motion of Sgr in this model is estimated to be (μlcos b, μb) = (−2.16, 1.73) mas yr−1, corresponding to a Galactocentric space velocity (U, V, W) = (230, −35, 195) km s−1 . Based on the velocity dispersion in the stellar tidal streams, we estimate that Sgr has a current bound mass MSgr = 2.5+1.3−1.0 × 108 M☉. We demonstrate that with simple assumptions about the star formation history of Sgr, tidal stripping models naturally give rise to gradients in the metallicity distribution function (MDF) along the stellar debris streams similar to those observed in recent studies. These models predict a strong evolution in the MDF of the model Sgr dwarf with time, indicating that the chemical abundances of stars in Sgr at the present day may be significantly different than the abundances of those already contributed to the Galactic stellar halo. We conclude by using the new N-body model to re-evaluate previous claims of the association of miscellaneous halo substructure with the Sgr dwarf.

Subfields: Astronomy and Astrophysics, Education, Instrumentation

View Paper: https://www.semanticscholar.org/paper/c64708157c630d5e2d79f95cab1ac7b5d7ad2482

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

In Education

In Instrumentation

Citations in the corpus

The shape of dark matter haloes in the Aquarius simulations: evolution and memory (2011, background): “More recently, Law et al. (2009); Law & Majewski (2010) have explored triaxial potentials with constant axis ratios, and found models that were able to fit simultaneously these constraints, albeit not completely satisfactorily.”
`Skinny Milky Way please', says Sagittarius (2014, methodology): “Thus, we attempt to build a rapid modelling algorithm that reproduces the salient features of tidal streams produced in N-body simulations such as that of Law & Majewski (2010).”
Modified Newtonian Dynamics (MOND): Observational Phenomenology and Relativistic Extensions (2011, methodology): “Yet another test would be the comparison of the observed Sagittarius stream [198, 248] with the predictions made for a disrupting galaxy satellite in the MOND potential of the Milky Way.”
The total mass of the Large Magellanic Cloud from its perturbation on the Orphan stream (2018, methodology): “…axis of the halo is within ∼20◦ of the orbital plane of the LMC. Interestingly, the orientation in the oblate case is consistent with the results Law & Majewski (2010) who fit the Sagittarius stream and found an almost MNRAS 487, 2685–2700 (2019) D ow nloaded from https://academ ic.oup.com /m…”
THE SHAPE OF THE INNER MILKY WAY HALO FROM OBSERVATIONS OF THE PAL 5 AND GD–1 STELLAR STREAMS (2016, methodology): “A successful model of the tidal tails of the Sgr dwarf galaxy has been found with b/a ≈ 0.7 (Law & Majewski 2010), but if this axis ratio is assumed in the inner ≈ 20 kpc, no model compatible with the observed Pal 5 tidal stream can be found (Pearson et al. 2015).”
Local-Group tests of dark-matter concordance cosmology - Towards a new paradigm for structure formation (2010, background): “Law & Majewski (2010) find a new slightly oblate solution to the MW DM halo shape at distances from 20 to 60 kpc.”
The influence of Sagittarius and the Large Magellanic Cloud on the stellar disc of the Milky Way Galaxy (2017, background): “…/m nras/article-abstract/481/1/286/5037931 by guest on 03 M ay 2019 when typically studying the stream of Sgr (Helmi & White 2001; Helmi 2004; Johnston, Law & Majewski 2005; Peñarrubia et al. 2010; Law & Majewski 2010), until just recently (Purcell et al. 2011; Gibbons, Belokurov & Evans 2017).”
ON THE SHOULDERS OF GIANTS: PROPERTIES OF THE STELLAR HALO AND THE MILKY WAY MASS DISTRIBUTION (2014, methodology): “Attempts to model these streams (Newberg et al. 2010; Law & Majewski 2010; Carlin et al. 2012) also provide an alternate constrain on the Galaxy mass.”
The Galaxy in Context: Structural, Kinematic, and Integrated Properties (2016, background): “Thus Law & Majewski (2010) proposed a triaxial halo model for the Milky Way that is in fact 580 Bland-Hawthorn · Gerhard A nn u.”
The local dark matter density (2014, neutral): “Early work on the stream suggested a near-spherical halo for the Milky Way (Ibata et al., 2001), but more recent data combined with more sophisticated modelling appear to favour a triaxial halo (Law & Majewski, 2010).”
The mass distribution and gravitational potential of the Milky Way (2016, methodology): “Famously, models of the Sagittarius stream have been used to argue that the dark-matter halo is oblate (e.g. Johnston, Law & Majewski 2005), prolateHelmi (2004) or triaxial (Law & Majewski 2010, though this is effectively oblate with the short axis in the plane of the Galaxy).”
SAGITTARIUS II, DRACO II AND LAEVENS 3: THREE NEW MILKY WAY SATELLITES DISCOVERED IN THE PAN-STARRS 1 3π SURVEY (2015, result): “The fact that it lies 40–45 kpc behind Sgr dSph rules out a direct connection between the two satellites but a comparison with the Law & Majewski (2010b) N-body model for the Sgr stream (Figure 5) reveals that Sgr II is located at the expected distance of model particles from the trailing arm of…”
THE CATALINA SURVEYS PERIODIC VARIABLE STAR CATALOG (2014, methodology): “In Figure 37, we plot the distribution of LPVs compared to the Sagittarius stream model of Law & Majewski (2010).”
Precession of the Sagittarius stream (2013, methodology): “Right: Comparison with the Sgr disruption model by Law & Majewski (2010) shown as grey-scale density.”
A COMPLETE SPECTROSCOPIC SURVEY OF THE MILKY WAY SATELLITE SEGUE 1: THE DARKEST GALAXY (2010, methodology): “Within 10◦ of Segue 1, the Law & Majewski (2010a) simulation contains & 200 times as many stars in the recently-stripped, leading (negative velocity) stream as are present in the older, trailing stream.”