Discovery of a Dynamical Cold Point in the Heart of the Sagittarius dSph Galaxy with Observations from the APOGEE Project

Abstract

The dynamics of the core of the Sagittarius (Sgr) dwarf spheroidal (dSph) galaxy are explored using high-resolution (R~22,500), H-band, near-infrared spectra of over 1,000 giant stars in the central 3 deg^2 of the system, of which 328 are identified as Sgr members. These data, among some of the earliest observations from the SDSS-III/Apache Point Observatory Galactic Evolution Experiment (APOGEE) and the largest published sample of high resolution Sgr dSph spectra to date, reveal a distinct gradient in the velocity dispersion of Sgr from 11-14 km/s for radii >0.8 degrees from center to a dynamical cold point of 8 km/s in the Sgr center --- a trend differing from that found in previous kinematical analyses of Sgr over larger scales that suggest a more or less flat dispersion profile at these radii. Well-fitting mass models with either cored and cusped dark matter distributions can be found to match the kinematical results, although the cored profile succeeds with significantly more isotropic stellar orbits than required for a cusped profile. It is unlikely that the cold point reflects an unusual mass distribution. The dispersion gradient may arise from variations in the mixture of populations with distinct kinematics within the dSph; this explanation is suggested (e.g., by detection of a metallicity gradient across similar radii), but not confirmed, by the present data. Despite these remaining uncertainties about their interpretation, these early test data (including some from instrument commissioning) demonstrate APOGEE's usefulness for precision dynamical studies, even for fields observed at extreme airmasses.

15 pages, 3 figures

References in corpus (14)

• The 2.5 m Telescope of the Sloan Digital Sky Survey
• New Grids of ATLAS9 Model Atmospheres
• The Observed properties of Dark Matter on small spatial scales
• Target Selection for the Apache Point Observatory Galactic Evolution Experiment (APOGEE)
• The kinematic status and mass content of the Sculptor dwarf spheroidal galaxy
• Does the Fornax dwarf spheroidal have a central cusp or core?
• The exotic chemical composition of the Sagittarius dwarf Spheroidal galaxy
• The nucleus of the Sagittarius dSph galaxy and M54: a window on the process of galaxy nucleation
• The ACS Survey of Galactic Globular Clusters: M54 and Young Populations in the Sagittarius Dwarf Spheroidal Galaxy
• Modeling The Structure And Dynamics of Dwarf Spheroidal Galaxies with Dark Matter And Tides
• Center-to-Limb Variation of Solar 3-D Hydrodynamical Simulations
• A near zero velocity dispersion stellar component in the Canes Venatici dwarf spheroidal galaxy
• The Michigan/MIKE Fiber System Survey of Stellar Radial Velocities in Dwarf Spheroidal Galaxies: Acquisition and Reduction of Data
• Multiple dynamical components in Local Group dwarf spheroidals

Cited by in corpus (31)

• The Apache Point Observatory Galactic Evolution Experiment (APOGEE)
• Sloan Digital Sky Survey IV: Mapping the Milky Way, Nearby Galaxies, and the Distant Universe
• Chemodynamics of the Milky Way. I. The first year of APOGEE data
• Disentangling the Galactic Halo with APOGEE: I. Chemical and Kinematical Investigation of Distinct Metal-Poor Populations
• The last breath of the Sagittarius dSph
• A Tail of Two Populations: Chemo-dynamics of the Sagittarius Stream and Implications for its Original Mass
• APOGEE Chemical Abundances of the Sagittarius Dwarf Galaxy
• Metallicity and $\alpha$-element Abundance Gradients along the Sagittarius Stream as Seen by APOGEE
• Chemical abundances in the nucleus of the Sagittarius dwarf spheroidal galaxy
• Multiple Chemodynamic Stellar Populations of the Ursa Minor Dwarf Spheroidal Galaxy
• Chemical abundances of hydrostatic and explosive alpha-elements in Sagittarius stream stars
• Identifying Sagittarius Stream Stars By Their APOGEE Chemical Abundance Signatures
• Upper Limit on the Milky Way Mass from the Orbit of the Sagittarius Dwarf Satellite
• The stellar velocity distribution function in the Milky Way galaxy
• A deep view into the nucleus of the Sagittarius Dwarf Spheroidal Galaxy with MUSE. II. Kinematic characterization of the stellar populations
• A Comparative Analysis of the Chemical Compositions of Gaia-Enceladus/Sausage and Milky Way Satellites using APOGEE
• Elemental Abundances in M31: First Alpha and Iron Abundance Measurements in M31's Giant Stellar Stream
• Solar and Stellar Photospheric Abundances
• Identifying Galactic Halo Substructure in 6D Phase-space Using $\sim$13,000 LAMOST K Giants
• Jurassic: A Chemically Anomalous Structure in the Galactic Halo
• Three-dimensional structure of the Sagittarius dSph core from RR Lyrae
• The Proper Motion of Pyxis: the first use of Adaptive Optics in tandem with HST on a faint halo object
• The metallicity distribution in the core of the Sagittarus dwarf spheroidal: minimising the metallicity biases
• The hELENa project - II. Abundance distribution trends of early-type galaxies: from dwarfs to giants
• Torus Models of the Outer Disc of the Milky Way using LAMOST Survey Data
• Chemical abundances and ages of the bulge stars in APOGEE high-velocity peaks
• A wide angle view of the Sagittarius dwarf spheroidal galaxy -- II. A CEMP-r/s star in the Sagittarius dwarf Spheroidal Galaxy
• A Sagittarius-like simulated dwarf spheroidal galaxy from TNG50
• Stellar Profile Independent Determination of the Dark Matter Distribution of the Fornax Local Group Dwarf Spheroidal Galaxy
• The chemical and spatial variations of the bulge's velocity ellipsoids
• Kinematics of the Sagittarius Dwarf Spheroidal core: A 5D Analysis for a 6D Methodology with Gaia DR3