J/ApJ/779/L6 3D kinematic observations of stars in Galactic Centre (Do+, 2013)
Three-dimensional stellar kinematics at the Galactic Center: measuring the
nuclear star cluster spatial density profile, black hole mass, and distance.
Do T., Martinez G.D., Yelda S., Ghez A., Bullock J., Kaplinghat M.,
Lu J.R., Peter A.H.G., Phifer K.
<Astrophys. J., 779, L6 (2013)>
=2013ApJ...779L...6D 2013ApJ...779L...6D
ADC_Keywords: Milky Way ; Parallaxes, spectroscopic ; Photometry, infrared ;
Radial velocities
Keywords: Galaxy: center; stars: kinematics and dynamics; stars: late-type;
techniques: high angular resolution; techniques: spectroscopic
Abstract:
We present three-dimensional (3D) kinematic observations of stars
within the central 0.5pc of the Milky Way (MW) nuclear star cluster
(NSC) using adaptive optics imaging and spectroscopy from the Keck
telescopes. Recent observations have shown that the cluster has a
shallower surface density profile than expected for a dynamically
relaxed cusp, leading to important implications for its formation and
evolution. However, the true 3D profile of the cluster is unknown due
to the difficulty in de-projecting the stellar number counts. Here, we
use spherical Jeans modeling of individual proper motions and radial
velocities to constrain, for the first time, the de-projected spatial
density profile, cluster velocity anisotropy, black hole mass (MBH),
and distance to the Galactic center (R0) simultaneously. We find
that the inner stellar density profile of the late-type stars,
ρ(r)∝r-γ, have a power law slope
γ=0.05_-0.60+0.29, much more shallow than the frequently
assumed Bahcall-Wolf slope of γ=7/4. The measured slope will
significantly affect dynamical predictions involving the cluster, such
as the dynamical friction time scale. The cluster core must be larger
than 0.5 pc, which disfavors some scenarios for its origin. Our
measurement of MBH=5.76-1.26+1.76x106M☉ and
R0=8.92-0.55+0.58kpc is consistent with that derived from
stellar orbits within 1" of Sgr A*. When combined with the orbit of
S0-2, the uncertainty on R0 is reduced by 30%
(8.46-0.38+0.42kpc). We suggest that the MW NSC can be used in the
future in combination with stellar orbits to significantly improve
constraints on R0.
Description:
Observations of the central 0.5pc were made using the integral-field
spectrograph OSIRIS and the imager NIRC2 on the Keck 2 telescope
between 2006 and 2010. These instruments are behind a laser-guide star
adaptive optics system. The spectroscopic observations are made along
the inclination angle of the young stellar disk, at a position angle
of 105° extending out to 14" from the Galactic center (GC). For
more details about the spectroscopic fields and data reduction, see Do
et al. (2013, J/ApJ/764/154), where the stellar identifications are
reported. Observations and data reduction for the imaging observations
are detailed in Yelda et al. (2014ApJ...783..131Y 2014ApJ...783..131Y).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 78 266 Measured stellar positions and velocities
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See also:
J/ApJ/764/154 : Stellar populations in the central 0.5pc. I. (Do+, 2013)
J/ApJ/725/331 : Astrometry in the Galactic Center (Yelda+, 2010)
J/A+A/511/A18 : NIR observations of stars near SgrA* (Schoedel+, 2010)
J/ApJ/703/1323 : Star spectroscopy in the Galaxy's nuclear cluster (Do+ 2009)
J/A+A/502/91 : Proper motions of stars near SgrA* (Schoedel+, 2009)
J/A+A/499/483 : NIR obs. of sources in galactic center (Buchholz+, 2009)
J/ApJ/699/186 : VLA observations of the Galactic center (Zhao+, 2009)
J/ApJ/681/1254 : Radial velocities of stars in the Galactic Center (Zhu+, 2008)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- Name Stellar identifier
9- 12 F4.1 mag Kmag [9.6/16.3] The K' band magnitude
14- 20 F7.4 arcsec oRA Offset in Right Ascension (1)
22- 28 F7.4 arcsec oDE Offset in Declination (1)
30- 34 F5.2 mas/yr xplx [-8.9/15.3] Parallax in the x direction
36- 39 F4.2 mas/yr e_xplx [0.02/0.8] Uncertainty in xplx
41- 46 F6.2 mas/yr yplx [-13.5/24.2] Parallax in the y direction
48- 51 F4.2 mas/yr e_yplx [0.02/1] Uncertainty in yplx
53- 60 F8.3 yr Epoch Epoch of the parallax observations
62- 65 I4 km/s RV [-738/597] Radial velocity
67- 69 I3 km/s e_RV [1/100] Statistical uncertainty in RV (2)
71- 78 F8.3 yr Ep.RV [2005.5/2010.6] Epoch of the RV observation
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Note (1): Where the offset is relative to Sgr A* at
17:45:40.03599 -29:00:28.1699 (J2000, Simbad)
Note (2): There is ∼3km/s systematic uncertainty from the wavelength solution.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 07-May-2015