The Bulge Radial Velocity Assay (BRAVA):I. Sample selection and a rotation curve

Results from the ongoing Bulge Radial Velocity Assay (BRAVA) are presented. BRAVA uses M red giant stars, selected from the 2MASS catalog to lie within a bound of reddening-corrected color and luminosity, as targets for the Cerro Tololo Inter-American Observatory 4 m Hydra multiobject spectrograph. Three years of observations investigate the kinematics of the Galactic bulge major (–10° < l < + 10°, b = − 4°) and minor (–6° < b < + 5°, -0.4° < l < 0.0°) axes with ~3300 radial velocities from 32 bulge fields and one disk field. We construct a longitude-velocity plot for the bulge stars and find that, contrary to previous studies, the bulge does not rotate as a solid body; from –4° < l < + 4° the rotation curve has a slope of roughly 100 km s−1 kpc−1 and flattens considerably at greater l, reaching a maximum rotation of 75 km s−1. We compare our rotation curve and velocity dispersion profile both to the self-consistent model of Zhao and to N-body models; neither fits both our observed rotation curve and velocity dispersion profile. We place the bulge on the plot of Vmax/σ vs. epsilon and find that the bulge lies near the oblate rotator line and very close to the parameters of NGC 4565, an edge-on spiral galaxy with a bulge similar to that of the Milky Way. We find that our summed velocity distribution of bulge stars appears to be sampled from a Gaussian distribution, with σ = 116 ± 2 km s−1 for our full data set. Two candidate cold streams are not confirmed with additional data.

[1]  D. Lynden-Bell,et al.  Review of galactic constants , 1986 .

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

[3]  R. M. Rich,et al.  Kinematics and Abundances of K Giants in the Nuclear Bulge of the Galaxy , 1990 .

[4]  D. Spergel,et al.  Microlensing by the galactic bar , 1994, astro-ph/9409022.

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

[6]  W. B. Burton,et al.  The gas distribution in the central region of the Galaxy. III - A barlike model of the inner-Galaxy gas based on improved H I data , 1980 .

[7]  V. Blanco,et al.  Giant M stars in Baade's Window , 1984 .

[8]  M. Skrutskie,et al.  The Two Micron All Sky Survey (2MASS) , 2006 .

[9]  K. Freeman,et al.  Dynamics of the Galactic Bulge Using Planetary Nebulae , 2000, astro-ph/0005086.

[10]  Ray M. Sharples,et al.  Kinematics of the late-M giants in Baade's window , 1990 .

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

[12]  L. Girardi,et al.  Theoretical isochrones in several photometric systems I. Johnson-Cousins-Glass, HST/WFPC2, HST/NICMOS, Washington, and ESO Imaging Survey filter sets , 2002, astro-ph/0205080.

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

[14]  A. J. Drake,et al.  The MACHO Project: Microlensing Optical Depth Toward the Galactic Bulge from Difference Image Analysis , 2000 .

[15]  B. Draine,et al.  Oscillatory instability of radiative shocks with transverse magnetic field : linear analysis and nonlinear simulations , 1992 .

[16]  Dante Minniti,et al.  Rotation of the Galactic bulge , 1992 .

[17]  HongSheng Zhao.  A steady-state dynamical model for the COBE-detected Galactic bar , 1996 .

[18]  UK,et al.  The photometric structure of the inner Galaxy , 1997 .

[19]  D. Reitzel,et al.  Kinematics and composition of the Galactic bulge: recent progress , 2007, Proceedings of the International Astronomical Union.

[20]  Andrew A. West,et al.  Evolution of the Bar Fraction in COSMOS: Quantifying the Assembly of the Hubble Sequence , 2007, 0710.4552.

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

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

[23]  Belgium,et al.  Evolution of asymptotic giant branch stars. II. Optical to far-infrared isochrones with improved TP- , 2007, 0711.4922.

[24]  James Liebert,et al.  The metallicity gradient of the Galactic bulge , 1995 .

[25]  N. Odegard,et al.  COBE diffuse infrared background experiment observations of Galactic reddening and stellar populations , 1994 .

[26]  Abundances of Baade's Window Giants from Keck HIRES Spectra. I. Stellar Parameters and [Fe/H] Values , 2005, astro-ph/0510408.

[27]  Takashi Onaka,et al.  SiO Maser Survey of the Galactic Bulge IRAS Sources. III. Kinematics of the Bulge Stars , 1995 .

[28]  D. Schlegel,et al.  Maps of Dust Infrared Emission for Use in Estimation of Reddening and Cosmic Microwave Background Radiation Foregrounds , 1998 .

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

[30]  Stefano Casertano,et al.  Transiting extrasolar planetary candidates in the Galactic bulge , 2006, Nature.

[31]  D. Schlegel,et al.  Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds , 1997, astro-ph/9710327.

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

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

[34]  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 .

[35]  Accepted to The Astrophysical Journal. Preprint typeset using L ATEX style emulateapj v. 10/09/06 A NEAR-INFRARED STUDY OF 2MASS BARS IN LOCAL GALAXIES: AN ANCHOR FOR HIGH REDSHIFT STUDIES , 2022 .

[36]  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.

[37]  A. Gould,et al.  Stellar Contribution to the Galactic Bulge Microlensing Optical Depth , 2003, astro-ph/0303309.

[38]  Dimitri Mihalas,et al.  Galactic Astronomy: Structure and Kinematics , 1981 .

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

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

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

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

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

[44]  J. Mould,et al.  The asymptotic giant branch of Magellanic cloud clusters , 1990 .

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

[46]  Rachel S. Somerville,et al.  ΛCDM-based Models for the Milky Way and M31. I. Dynamical Models , 2001, astro-ph/0110390.

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

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

[49]  M. Franx,et al.  A new method for the identification of non-Gaussian line profiles in elliptical galaxies , 1993 .

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