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Kinematics at the edge of the galactic bulge: evidence for cylindrical rotation

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  • Christian D. Howard
  • R. Michael Rich
  • Will Clarkson
  • Ryan Mallery
  • John Kormendy
  • Roberto de Propris
  • Annie C. Robin
  • Roger Fux
  • David B. Reitzel
  • HongSheng Zhao
  • Konrad Kuijken
  • Andreas Koch
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<mark>Journal publication date</mark>24/08/2009
<mark>Journal</mark>Astrophysical Journal Letters
Issue number2
Volume702
Number of pages5
Pages (from-to)L153-L157
Publication StatusPublished
<mark>Original language</mark>English

Abstract

We present new results from BRAVA, a large-scale radial velocity survey of the Galactic bulge, using M giant stars selected from the Two Micron All Sky Survey catalog as targets for the Cerro Tololo Inter-American Observatory 4 m Hydra multi-object spectrograph. The purpose of this survey is to construct a new generation of self-consistent bar models that conform to these observations. We report the dynamics for fields at the edge of the Galactic bulge at latitudes b = –8° and compare to the dynamics at b = –4°. We find that the rotation curve V(r) is the same at b = –8° as at b = –4°. That is, the Galactic boxy bulge rotates cylindrically, as do boxy bulges of other galaxies. The summed line-of-sight velocity distribution at b = –8° is Gaussian, and the binned longitude-velocity plot shows no evidence for either a (disk) population with cold dynamics or for a (classical bulge) population with hot dynamics. The observed kinematics are well modeled by an edge-on N-body bar, in agreement with published structural evidence. Our kinematic observations indicate that the Galactic bulge is a prototypical product of secular evolution in galaxy disks, in contrast with stellar population results that are most easily understood if major mergers were the dominant formation process.