2011ApJ...728..100M

We present the first direct measurement of the central black hole mass, M_•, in NGC 6086, the Brightest Cluster Galaxy (BCG) in A2162. Our investigation demonstrates for the first time that stellar-dynamical measurements of M_• in BCGs are possible beyond the nearest few galaxy clusters. We observed NGC 6086 with laser guide star adaptive optics and the integral-field spectrograph (IFS) OSIRIS at the W. M. Keck Observatory and with the seeing-limited IFS GMOS-N at Gemini Observatory North. We combined the IFS data sets with existing major-axis kinematics and used axisymmetric stellar orbit models to determine M_• and the R-band stellar mass-to-light ratio, M_{sstarf}/L_R . We find M_•= 3.6^+1.7_–1.1x10⁹ M_☉and M_{sstarf}/L _R= 4.6^+0.3_–0.7M_☉L_☉^–1 (68% confidence) from models using the most massive dark matter halo allowed within the gravitational potential of the host cluster. Models fitting only IFS data confirm M_• ∼ 3x10⁹ M_☉ and M_{sstarf}/L_R∼ 4 M_☉L_/☉, with weak dependence on the assumed dark matter halo structure. When data out to 19 kpc are included, the unrealistic omission of dark matter causes the best-fit black hole mass to decrease dramatically, to 0.6x10⁹ M_☉, and the best-fit stellar mass-to-light ratio to increase to 6.7 M_☉ L^–1_☉,R. The latter value is at further odds with stellar population studies favoring M_{sstarf}/L_R∼ 2 M_☉ L^–1_☉. Biases from dark matter omission could extend to dynamical models of other galaxies with stellar cores, and revised measurements of M_• could steepen the empirical scaling relationships between black holes and their host galaxies.