Bibcode
DOI
Woodley, Kristin A.; Harris, William E.; Beasley, Michael A.; Peng, Eric W.; Bridges, Terry J.; Forbes, Duncan A.; Harris, Gretchen L. H.
Bibliographical reference
The Astronomical Journal, Volume 134, Issue 2, pp. 494-510.
Advertised on:
8
2007
Citations
75
Refereed citations
71
Description
A new kinematic and dynamic study of the halo of the giant elliptical
galaxy NGC 5128 is presented. From a spectroscopically confirmed sample
of 340 globular clusters and 780 planetary nebulae, the rotation
amplitude, rotation axis, velocity dispersion, and total dynamical mass
are determined for the halo of NGC 5128. The globular cluster kinematics
were searched for both radial dependence and metallicity dependence by
subdividing the globular cluster sample into 158 metal-rich
([Fe/H]>-1.0) and 178 metal-poor ([Fe/H]<-1.0) globular clusters.
Our results show that the kinematics of the metal-rich and metal-poor
subpopulations are quite similar: over a projected radius of 0-50 kpc,
the mean rotation amplitudes are 47+/-15 and 31+/-14 km s-1
for the metal-rich and metal-poor populations, respectively. There is a
indication within 0-5 kpc that the metal-poor clusters have a lower
rotation signal than in the outer regions of the galaxy. The rotation
axis shows an interesting twist at 5 kpc, agreeing with the
zero-velocity curve presented by Peng and coworkers. Within 5 kpc both
metal-rich and metal-poor populations have a rotation axis nearly
parallel to the north-south direction, which is 0°, while beyond 5
kpc the rotation axis twists ~180°. The velocity dispersion displays
a steady increase with galactocentric radius for both metallicity
populations, with means of 111+/-6 and 117+/-6 km s-1 within
a projected radius of 15 kpc for the metal-rich and metal-poor
populations; however, the outermost regions suffer from low number
statistics and spatial biases. The planetary nebula kinematics are
slightly different. Out to a projected radius of 90 kpc from the center
of NGC 5128, the planetary nebulae have a higher rotation amplitude of
76+/-6 km s-1 and a rotation axis of
170deg+/-5deg east of north, with no significant
radial deviation in either determined quantity. The velocity dispersion
decreases with galactocentric distance. The total mass of NGC 5128 is
found using the tracer mass estimator, described by Evans et al., to
determine the mass supported by internal random motions and the
spherical component of the Jeans equation to determine the mass
supported by rotation. We find a total mass of
(1.0+/-0.2)×1012 Msolar from the planetary
nebula data extending to a projected radius of 90 kpc. The similar
kinematics of the metal-rich and metal-poor globular clusters allow us
to combine the two subpopulations to determine an independent estimate
of the total mass, giving (1.3+/-0.5)×1012
Msolar out to a projected radius of 50 kpc. Lastly, we
publish a new and homogeneous catalog of known globular clusters in NGC
5128. This catalog combines all previous definitive cluster
identifications from radial velocity studies and HST imaging studies, as
well as 80 new globular clusters with radial velocities from a study of
M. A. Beasley et al. (in preparation).