Kinematics of bulge giants in F588

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Abstract

Radial velocities for 331 stars in the F588 bulge field at l, b = (8°, 7°) are obtained. The mean Galactocentric velocity for 319 stars with R ≤ 12.3 is 〈V〉 = 54.4 ± 4.7 km s-1, and the velocity dispersion is σ = 84.4 ± 3.3 km s-1. These stars have metal abundances based on a set of spectral indices calibrated against a grid of ∼400 standard stars. Dividing the sample according to metallicity, the halo and bulge components are kinematically distinct. The 65 K giants with [Fe/H] ≤ -1 (mostly halo giants) have 〈V〉 = - 7.0 ± 13.6 km s-1 and σ = 109.4 ± 9.6 km s-1. The 31 "pure" halo giants (with [Fe/H] ≤ - 1.5) have 〈V〉 = -5.8 ± 20.4 km s-1 and σ = 113.5 ± 14.4 km s-1. The mean Galactocentric velocity and velocity dispersion for 194 bulge K giants (stars with [Fe/H] ≥ -1.0) are 〈V〉 = 65.9 ± 5.1 km s-1 and σv = 71.9 ± 3.6 km s-1. The difference between halo and bulge kinematics is of very high statistical significance. The Galactic bulge and halo are distinct components, defined by consistency among [Fe/H], 〈V〉, and σ. Bulge giants are also found to have their kinematics correlated with their metallicities. After discussing other possible causes, including disk and halo contamination, it is argued that this effect is real. The kinematics of 26 M giants in our sample are compared with those of other evolved bulge tracers (Mira variables, OH/IR stars, SiO masers, etc.). These M giants observed in the field have kinematics consistent with their being bulge members. The dependence of velocity dispersion on distance from the Galactic center is determined by combining the data with existing data from Baade's window. While the line-of-sight velocity dispersion of the bulge giants decreases steeply with distance from the Galactic center, that of halo giants decreases very slowly if at all. The mass in the inner 1.5 kpc is determined to be M1.5 = (1.38 ± 0.26) × 1010 M and M1.5 = (1.74 ± 0.28) × 1010 M for the cases of isotropic and anisotropic inner halo, respectively. On the basis of kinematics and metallicities, we conclude that the bulge is a distinct galactic component and not the inner extension of the halo, thin disk, or thick disk.

Original languageEnglish
Pages (from-to)579-599
Number of pages21
JournalAstrophysical Journal
Volume459
Issue number2 PART I
DOIs
Publication statusPublished - 1996

Keywords

  • Galaxy: kinematics and dynamics
  • Galaxy: stellar content
  • Techniques: radial velocities

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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