Kinematics of the Galactic Halo from Horizontal Branch stars in the Hamburg/ESO Survey

Abstract

Large samples of Field Horizontal Branch (FHB) stars make excellent tracers of the Galactic halo; by studying their kinematics, one can infer important physical properties of our Galaxy. Here we present the results of a medium-resolution spectroscopic survey of 530 FHB stars selected from the Hamburg/ESO survey. The stars have a mean distance of ~7 kpc and thus probe the inner parts of the Milky Way halo. We measure radial velocities from the spectra in order to test the model of Sommer-Larsen et al., who suggested that the velocity ellipsoid of the halo changes from radially-dominated orbits to tangentially-dominated orbits as one proceeds from the inner to the outer halo. We find that the present data are unable to discriminate between this model and a more simple isothermal ellipsoid; we suggest that additional observations towards the Galactic centre might help to differentiate them.

7 pages, 7 figures. Accepted for publication in MNRAS

References in corpus (5)

• Blue horizontal branch stars in the Sloan Digital Sky Survey: I. Sample selection and structure in the Galactic halo
• Blue horizontal branch stars in the Sloan Digital Sky Survey: II. Kinematics of the Galactic halo
• Distant field BHB stars and the mass of the Galaxy II: Photometry and spectroscopy of UKST candidates 16<B<19.5, 11<R<52 kpc
• Surveying the Inner Halo of the Galaxy with 2MASS-Selected Horizontal Branch Candidates
• The stellar content of the Hamburg/ESO survey. III. Field horizontal-branch stars in the Galaxy

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• Constraints on the assembly history of the Milky Way's smooth, diffuse stellar halo from the metallicity-dependent, radially-dominated velocity anisotropy profiles probed with K giants and BHB stars using LAMOST, SDSS/SEGUE, and Gaia
• Kinematic Structure in the Galactic Halo at the North Galactic Pole: RR Lyrae and BHB Stars show different kinematics
• Very Metal-Poor Outer-Halo Stars with Round Orbits
• A Catalog of Candidate Field Horizontal-Branch and A-Type Stars. III. A 2MASS-Cleaned Version
• VVV Survey of Blue Horizontal-Branch Stars in the Bulge-Halo Transition Region of the Milky Way
• On the robustness of the velocity anisotropy parameter in probing the stellar kinematics in Milky Way like galaxies: Take away from TNG50 simulation
• Fading Features Found in the Kinematics of the Far-Reaching Milky Way Stellar Halo