A Two Micron All Sky Survey View of the Sagittarius Dwarf Galaxy. II. Swope Telescope Spectroscopy of M Giant Stars in the Dynamically Cold Sagittarius Tidal Stream

By S. Majewski, W. Kunkel, D. Law, R. Patterson, A. Polak, H. Rocha-Pinto, J. Crane, P. Frinchaboy, Cameron Hummels, K. Johnston and 3 more. 2004

132 citations recorded by the source corpus.

We have obtained moderate resolution (∼6 km s-1) spectroscopy of several hundred M giant candidates selected from Two Micron All Sky Survey photometry. Radial velocities are presented for stars mainly in the southern Galactic hemisphere, and the primary targets have Galactic positions consistent with association to the tidal tail system of the Sagittarius (Sgr) dwarf galaxy. M giant stars selected from the apparent trailing debris arm of Sgr have velocities showing a clear trend with orbital longitude, as expected from models of the orbit and destruction of Sgr. A minimum 8 kpc width of the trailing stream about the Sgr orbital midplane is implied by verified radial velocity members. The coldness of this stream (σv ∼ 10 km s-1) provides upper limits on the combined contributions of stream heating by a lumpy Galactic halo and the intrinsic dispersion of released stars, which is a function of the Sgr core mass. We find that the Sgr trailing arm is consistent with a Galactic halo that contains one dominant, LMC-like lump; however, some lumpier halos are not ruled out. An upper limit to the total mass-to-light ratio of the Sgr core is 21 in solar units. Evidence for other velocity structures is found among the more distant (>13 kpc) M giants. A second structure that roughly mimics expectations for wrapped, leading Sgr arm debris crosses the trailing arm in the southern hemisphere; however, this may also be an unrelated tidal feature. Among the bright, nearby (<13 kpc) M giants toward the south Galactic pole are a number with large velocities that identify them as halo stars; these too may trace halo substructure, perhaps part of the Sgr leading arm near the Sun. The positions and velocities of southern hemisphere M giants are compared with those of southern hemisphere globular clusters potentially stripped from the Sgr system. Support for association of the globular clusters Pal 2 and Pal 12 with Sgr debris is found, based on positional and radial velocity matches. Our discussion includes description of a masked-filtered cross-correlation methodology that achieves better than 1/20 of a resolution element velocities in moderate-resolution spectra. The improved velocity resolution achieved allows tighter constraints to be placed on the coldness of the Sgr stream than previously established.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/1e7dc6b923bcb3e14b3949244a71242837b89ac7

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In Astronomy and Astrophysics

1. A. Helmi
2. S. Majewski
3. M. Walker
4. L. Strigari
5. N. Evans II
6. James S. Bullock
7. D. Law
8. V. Belokurov

Citations in the corpus

• THE SAGITTARIUS DWARF GALAXY: A MODEL FOR EVOLUTION IN A TRIAXIAL MILKY WAY HALO (2010, methodology): “10 Note that while we use the Monaco et al. (2007) velocity dispersion to derive the mass of Sgr, we used the Majewski et al. (2004) velocity dispersion in Equation 10 because this was the value appropriate to that more extensive sample of stars used to define the velocity trend of the trailing…”
• ASSESSING THE MILKY WAY SATELLITES ASSOCIATED WITH THE SAGITTARIUS DWARF SPHEROIDAL GALAXY (2010, methodology): “This agreement is particularly notable for the T1 arm since this may demonstrate that the LM10 model is consistent with observations at least 60◦ further along this arm than has been previously constrained by the M-giant observations of Majewski et al. (2004).”
• A Two Micron All-Sky Survey View of the Sagittarius Dwarf Galaxy. IV. Modeling the Sagittarius Tidal Tails (2004, background): “…spectroscopy of Sgr candidate stars has determined line-of-sight (i.e., ‘‘radial’’) velocities for SgrM giant stars throughout the trailing tail (Majewski et al. 2004, hereafter Paper II), and work on stars in the leading trail is in progress (S. R. Majewski et al. 2005, in preparation,…”
• Velocity Trends in the Debris of Sagittarius and the Shape of the Dark Matter Halo of Our Galaxy (2004, background): “The results have been presented in Law et al. (2004) and in tabular form (for the trailing stream) in Majewski et al. 2004 (hereafter M04).”
• The Velocity Dispersion Profile of the Remote Dwarf Spheroidal Galaxy Leo I: A Tidal Hit and Run? (2007, methodology): “This model provides an elegant solution to the puzzle of the long-term survivability of Sgr (Zhao 1998; Bellazzini et al. 2006) and is consistent with its detailed orbital characteristics (Majewski et al. 2004).”
• The ACS Survey of Galactic Globular Clusters: M54 and Young Populations in the Sagittarius Dwarf Spheroidal Galaxy (2007, methodology): “…with Sgr clusters near the core (Terzan 7, Terzan 8, and Arp 2; Ibata et al. 1994) or in the Sgr tidal stream (Pal 12 [Dinescu et al. 2000], Pal 2 [Majewski et al. 2004], and Whiting 1 [Carraro et al. 2007]), Sgr has an age-metallicity relation (AMR) consistent with a simple closed-box model…”
• THE LEAST-LUMINOUS GALAXY: SPECTROSCOPY OF THE MILKY WAY SATELLITE SEGUE 1 (2008, background): “Similarly, for no model are trailing Sgr debris spatially coincident with Segue 1 while simultaneously reproducing the trend of trailing M-giant velocities observed by Majewski et al. (2004).”
• Exploring Halo Substructure with Giant Stars. XI. The Tidal Tails of the Carina Dwarf Spheroidal Galaxy and the Discovery of Magellanic Cloud Stars in the Carina Foreground (2006, background): “The Sagittarius paradigm: All of the observed spatial and dynamical features in Carina are also found in the one undisputed case of dSph tidal disruption in the Milky Way — the Sagittarius dSph (see Sgr spatial and velocity properties given in Majewski et al. 2003, 2004a).”
• The Origin of the Bifurcation in the Sagittarius Stream (2006, methodology): “The morphology of the Sgr stream is known in detail in the Galactic southern hemisphere thanks to 2MASS (Majewski et al. 2003, 2004; Skrutskie et al. 2006).”
• The QUEST RR Lyrae Survey. II. The Halo Overdensities in the First Catalog (2006, background): “Thedistributions of these stars and the measurements of radial velocities for subsamples (e.g., Dohm-Palmer et al. 2001; Majewski et al. 2004; Vivas et al. 2005) provide conclusive proof that this feature is part of the leading stream from the Sagittarius dSph galaxy.”