Abstract
- [*] Hubble Space Telescope evidence for an intermediate-mass black
hole in the globular cluster M15 - II. Kinematical analysis and
dynamical modeling
- Gerssen J., van der Marel R.P., Gebhardt K., Guhathakurta P.,
Peterson R., Pryor, C.
- AJ, 124, 3270-3288, 2002
-
- [*]
Citations to
this paper in the ADS
We analyze HST/STIS spectra (see Paper I) of the central region of the dense
globular cluster M15. We infer the velocities of 64 individual stars,
two-thirds of which have their velocity measured for the first time. This
triples the number of stars with measured velocities in the central 1 arcsec
of M15 and doubles the number in the central 2 arcsec. Combined with existing
ground-based data we obtain the radial profiles of the projected kinematical
quantities. The RMS velocity sigma_RMS rises to 14 km/s in the central few
arcsec, somewhat higher than the values of 10-12 km/s inferred previously from
ground-based data. To interpret the results we construct dynamical models
based on the Jeans equation, which imply that M15 must have a central
concentration of non-luminous material. If this is due to a single black hole,
then its mass is M_BH = (3.9 +/- 2.2) x 10^3 solar masses. This is consistent
with the relation between M_BH and sigma_RMS that has been established for
galaxies. Also, the existence of intermediate-mass black holes in globular
clusters is consistent with several scenarios for globular cluster evolution
proposed in the literature. Therefore, these results may have important
implications for our understanding of the evolution of globular clusters, the
growth of black holes, the connection between globular cluster and galaxy
formation, and the nature of the recently discovered `ultra-luminous' X-ray
sources in nearby galaxies. Instead of a single black hole, M15 could have a
central concentration of dark remnants (e.g., neutron stars) due to mass
segregation. However, the best-fitting Fokker-Planck models that have
previously been constructed for M15 do not predict a central mass
concentration that is sufficient to explain the observed kinematics.[ABRIDGED]
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Last modified November 29, 2002.
Roeland van der Marel,
marel@stsci.edu.
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