The Most Distant Stars in the Milky Way

Abstract

We report on the discovery of the most distant Milky Way (MW) stars known to date: ULAS J001535.72$+$015549.6 and ULAS J074417.48$+$253233.0. These stars were selected as M giant candidates based on their infrared and optical colors and lack of proper motions. We spectroscopically confirmed them as outer halo giants using the MMT/Red Channel spectrograph. Both stars have large estimated distances, with ULAS J001535.72$+$015549.6 at $274\pm 74$ kpc and ULAS J074417.48$+$253233.0 at 238 $\pm$ 64 kpc, making them the first MW stars discovered beyond 200 kpc. ULAS J001535.72$+$015549.6 and ULAS J074417.48$+$253233.0 are both moving away from the Galactic center at $52\pm 10$ km s${}^{-1}$ and $24\pm 10$ km s${}^{-1}$, respectively. Using their distances and kinematics, we considered possible origins such as: tidal stripping from a dwarf galaxy, ejection from the MW's disk, or membership in an undetected dwarf galaxy. These M giants, along with two inner halo giants that were also confirmed during this campaign, are the first to map largely unexplored regions of our Galaxy's outer halo.

Accepted and in print by ApJL. Seven pages, 2 figures

References in corpus (43)

• The Sloan Digital Sky Survey: Technical Summary
• The Structure of Cold Dark Matter Halos
• Validation of the new Hipparcos reduction
• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• The observed properties of dwarf galaxies in and around the Local Group
• GAIA: Composition, Formation and Evolution of the Galaxy
• A 2MASS All-Sky View of the Sagittarius Dwarf Galaxy: I. Morphology of the Sagittarius Core and Tidal Arms
• Tracing Galaxy Formation with Stellar Halos I: Methods
• The Universal Stellar Mass-Stellar Metallicity Relation for Dwarf Galaxies
• LCDM-based models for the Milky Way and M31 I: Dynamical Models
• The RAVE Survey: Constraining the Local Galactic Escape Speed
• The Sagittarius Dwarf Galaxy: a Model for Evolution in a Triaxial Milky Way Halo
• The accretion origin of the Milky Way's stellar halo
• The Milky Way's circular velocity curve between 4 and 14 kpc from APOGEE data
• Discovery of an Unbound Hyper-Velocity Star in the Milky Way Halo
• The Dual Origin of Stellar Halos
• The RAVE survey: the Galactic escape speed and the mass of the Milky Way
• The radial velocity dispersion profile of the Galactic halo: Constraining the density profile of the dark halo of the Milky Way
• Science performance of Gaia, ESA's space-astrometry mission
• Precession of the Sagittarius stream
• Stellar Populations in the Large Magellanic Cloud from 2MASS
• Milky Way Mass Models for Orbit Calculations
• The properties of dynamically ejected runaway and hyper-runaway stars
• The cold veil of the Milky Way stellar halo
• A Grand Rotation Curve and Dark Matter Halo in the Milky Way Galaxy
• Broken degeneracies: the rotation curve and velocity anisotropy of the Milky Way halo
• Tracing Sagittarius Structure with SDSS and SEGUE Imaging and Spectroscopy
• Evidence for a Milky Way Tidal Stream Reaching Beyond 100 kpc
• Where are the Fossils of the First Galaxies? II. True Fossils, Ghost Halos, and the Missing Bright Satellites
• MASE: A New Data--Reduction Pipeline for the Magellan Echellette Spectrograph
• The SEGUE K giant survey II: A Catalog of Distance Determinations for the SEGUE K giants in the Galactic Halo
• Insight Into the Formation of the Milky Way Through Cold Halo Substructure. I. The ECHOS of Milky Way Formation
• The APM Survey for Cool Carbon Stars in the Galactic Halo - II The Search for Dwarf Carbon Stars
• Stealth Galaxies in the Halo of the Milky Way
• S-stars in the Galactic center and hypervelocity stars in the Galactic halo: two faces of the tidal breakup of stellar binaries by the central massive black hole?
• Selection of Metal-poor Giant Stars Using the Sloan Digital Sky Survey Photometric System
• Group finding in the stellar halo using M-giants in 2MASS: An extended view of the Pisces Overdensity?
• Cool carbon stars in the halo: a new survey based on 2MASS
• New observations of cool carbon stars in the halo
• Hunting The Most Distant Stars in the Milky Way: Methods and Initial Results
• Cool carbon stars in the halo II. A study of 25 new objects
• Properties of Galactic Dark Matter: Constraints from Astronomical Observations
• Identifying High Metallicity M Giants at Intragroup Distances with SDSS

Cited by in corpus (12)

• The Best and Brightest Metal-Poor Stars
• Predicted Extension of the Sagittarius Stream to the Milky Way Virial Radius
• The Edge of the Galaxy
• Discovery of distant RR Lyrae stars in the Milky Way using DECam
• The Outer Halo of the Milky Way as Probed by RR Lyr Variables from the Palomar Transient Facility
• Age Gradients Throughout the Galaxy with O-Miras
• To the Galactic Virial Radius with Hyper Suprime-Cam
• The UV Emission of Stars in LAMOST Survey I. Catalogs
• New views of the distant stellar halo
• They Might Be Giants: An Efficient Color-Based Selection of Red Giant Stars
• Astrometry with the Wide-Field InfraRed Space Telescope
• A catalogue of oxygen-rich pulsating giants in the galactic halo and the Sagittarius stream