Limits on intermediate-mass black holes in six Galactic globular clusters with integral-field spectroscopy. (arXiv:1212.3475v1 [astro-ph.GA])

Limits on intermediate-mass black holes in six Galactic globular clusters with integral-field spectroscopy. (arXiv:1212.3475v1 [astro-ph.GA]):
The formation of supermassive black holes at high redshift still remains a
puzzle to astronomers. Their growth becomes reasonable only when starting from
a massive seed black hole with mass of the order of 10^2 - 10^5 M_SUN.
Intermediate-mass black holes (IMBHs) are therefore an important field of
research. Especially the possibility of finding them in the centers of globular
clusters has recently drawn attention. The search for IMBHs in the centers of
globular clusters could therefore shed light on the process of black-hole
formation and cluster evolution. We are investigating six galactic globular
clusters for the presence of an IMBH at their centers. Based on their kinematic
and photometric properties, we selected the globular clusters NGC 1851, NGC
1904 (M79), NGC 5694, NGC 5824, NGC 6093 (M80) and NGC 6266 (M62). We use
integral field spectroscopy in order to obtain the central velocity-dispersion
profile of each cluster. We compute the cluster photometric center and the
surface brightness profile using HST data. After combining these datasets we
compare them to analytic Jeans models. We use varying M/L_V profiles for
clusters with enough data points in order to reproduce their kinematic profiles
in an optimal way. Finally, we vary the mass of the central black hole and test
whether the cluster is better fitted with or without an IMBH. We present the
statistical significance, including upper limits, of the black-hole mass for
each cluster. NGC 1904 and NGC 6266 provide the highest significance for a
black hole. Jeans models in combination with a M/L_V profile obtained from
N-body simulations (in the case of NGC 6266) predict a central black hole of
M_BH = (3 +- 1) x 10^3 M_SUN for NGC 1904 and M_BH = (2 +- 1) x 10^3 M_SUN for
NGC 6266. Furthermore, we discuss the possible influence of dark remnants and
mass segregation at the center of the cluster on the detection of an IMBH.