KINEMATICS AT THE EDGE OF THE GALACTIC BULGE: EVIDENCE FOR CYLINDRICAL ROTATION

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.

[1]  A consistent microlensing model for the Galactic bar , 1995, astro-ph/9512065.

[2]  E. Athanassoula,et al.  Morphology, photometry and kinematics of N‐body bars – I. Three models with different halo central concentrations , 2001, astro-ph/0111449.

[3]  A. McWilliam,et al.  TWO RED CLUMPS AND THE X-SHAPED MILKY WAY BULGE , 2010, 1008.0519.

[4]  K. Stanek,et al.  FABRY–PEROT ABSORPTION LINE SPECTROSCOPY OF THE GALACTIC BAR. I. KINEMATICS , 2008, 0810.1225.

[5]  R. Rich,et al.  The First Detailed Abundances for M Giants in Baade’s Window from Infrared Spectroscopy , 2005, astro-ph/0506051.

[6]  B. Jarvis The NGC 128 Group of Galaxies , 1990 .

[7]  G. Gilmore,et al.  The structure of the Galactic bar , 2005, astro-ph/0501383.

[8]  R. Rich,et al.  Near-coeval formation of the Galactic bulge and halo inferred from globular cluster ages , 1995, Nature.

[9]  C. Norman,et al.  Dissipation in barred galaxies: the growth of bulges and central mass concentrations , 1990 .

[10]  R. Launhardt,et al.  The Nuclear Bulge of the Galaxy. III. Large-Scale Physical Characteristics of Stars and Interstellar Matter , 2002, astro-ph/0201294.

[11]  M. Schultheis,et al.  Infrared stellar populations in the central parts of the Milky Way galaxy , 2002, astro-ph/0210073.

[12]  G. Illingworth,et al.  Rotation of the bulge components of disk galaxies. , 1982 .

[13]  M. Livio,et al.  Stellar Proper Motions in the Galactic Bulge from Deep Hubble Space Telescope ACS WFC Photometry , 2008, 0809.1682.

[14]  R. Rich,et al.  The First Detailed Abundances for M Giants in the Inner Bulge from Infrared Spectroscopy , 2007, 0707.1855.

[15]  Andreas Koch,et al.  The Bulge Radial Velocity Assay (BRAVA):I. Sample selection and a rotation curve , 2008, 0807.3967.

[16]  J. A. Sellwood,et al.  Dynamics of Barred Galaxies , 1993 .

[17]  J. Frogel,et al.  M giants in Baade's window: infrared colors, luminosities, and implications for the stellar content of E and S0 galaxies , 1987 .

[18]  David N. Spergel,et al.  Direct evidence for a bar at the Galactic center , 1991 .

[19]  R. Michael Rich,et al.  Abundances of Baade’s Window Giants from Keck HIRES Spectra. II. The Alpha and Light Odd Elements , 2006, astro-ph/0609087.

[20]  R. Rosenfeld Nature , 2009, Otolaryngology--head and neck surgery : official journal of American Academy of Otolaryngology-Head and Neck Surgery.

[21]  A. Udalski,et al.  MODELLING THE GALACTIC BAR USING RED CLUMP GIANTS , 1996 .

[22]  R. Rich,et al.  The First Detailed Abundance Analysis of Galactic Bulge K Giants in Baade's Window , 1994 .

[23]  R. Rich,et al.  The Bulge Radial Velocity Assay: Techniques and a Rotation Curve , 2006, astro-ph/0611403.

[24]  S. Picaud,et al.  3D outer bulge structure from near infrared star counts , 2004, astro-ph/0407361.

[25]  Oxygen, Sodium, Magnesium and Aluminium as tracers of the Galactic Bulge Formation , 2006, astro-ph/0610346.

[26]  L. Greggio,et al.  Age and Metallicity Distribution of the Galactic Bulge from Extensive Optical and Near-IR Stellar Photometry , 2003 .

[27]  S. Ortolani,et al.  The metal content of bulge field stars from FLAMES-GIRAFFE spectra - I. Stellar parameters and iron abundances , 2008, 0805.1218.

[28]  R. A. James,et al.  A dynamical instability of bars in disk galaxies , 1991, Nature.

[29]  David T. Leisawitz,et al.  The COBE Diffuse Infrared Background Experiment Search for the Cosmic Infrared Background. III. Separation of Galactic Emission from the Infrared Sky Brightness , 1998, astro-ph/9805323.

[30]  N. Bissantz,et al.  Spiral arms, bar shape and bulge microlensing in the Milky Way , 2001, astro-ph/0110368.

[31]  R. Rich,et al.  Evidence of a Metal-rich Galactic Bar from the Vertex Deviation of the Velocity Ellipsoid , 2006, astro-ph/0611433.

[32]  Samuel Harvey Moseley,et al.  COBE diffuse infrared background experiment observations of the galactic bulge , 1994 .

[33]  Samuel Harvey Moseley,et al.  Morphology, near infrared luminosity, and mass of the galactic bulge from Cobe dirbe observations , 1995 .

[34]  R. Wielen Dynamics and Interactions of Galaxies , 1990 .

[35]  Formation and evolution of the Galactic bulge: constraints from stellar abundances , 2006, astro-ph/0611650.

[36]  On the nature of bulges in general and of box/peanut bulges in particular: input from N-body simulations , 2005 .

[37]  Robert C. Kennicutt,et al.  Secular Evolution and the Formation of Pseudobulges in Disk Galaxies , 2004, astro-ph/0407343.