Abstract
We investigate the presence of a central black hole (BH) in B023-G078, M31's most massive globular cluster. We present high-resolution, adaptive-optics assisted, integral-field spectroscopic kinematics from Gemini/NIFS that show a strong rotation (∼20 km s−1) and a velocity dispersion rise toward the center (37 km s−1). We combine the kinematic data with a mass model based on a two-component fit to HST ACS/HRC data of the cluster to estimate the mass of a putative BH. Our dynamical modeling suggests a >3σ detection of a BH component of
9.1
−
2.8
+
2.6
×
10
4
M
⊙
(1σ uncertainties). The inferred stellar mass of the cluster is
6.22
−
0.05
+
0.03
×
10
6
M
⊙
, consistent with previous estimates, thus the BH makes up 1.5% of its mass. We examine whether the observed kinematics are caused by a collection of stellar mass BHs by modeling an extended dark mass as a Plummer profile. The upper limit on the size scale of the extended mass is 0.56 pc (95% confidence), which does not rule out an extended mass. There is compelling evidence that B023-G078 is the tidally stripped nucleus of a galaxy with a stellar mass >109
M
⊙, including its high-mass, two-component luminosity profile, color, metallicity gradient, and spread in metallicity. Given the emerging evidence that the central BH occupation fraction of >109
M
⊙ galaxies is high, the most plausible interpretation of the kinematic data is that B023-G078 hosts a central BH. This makes it the strongest BH detection in a lower-mass (<107
M
⊙) stripped nucleus, and one of the few dynamically detected intermediate-mass BHs.
VVV SURVEY OBSERVATIONS OF A MICROLENSING STELLAR MASS BLACK HOLE CANDIDATE IN THE FIELD OF THE GLOBULAR CLUSTER NGC 6553
