We present a revised measurement of the mass of the central black hole ( { { \mathrm { M } } _ { BH } } ) in the Seyfert 1 galaxy NGC 4151 .
The new stellar dynamical mass measurement is derived by applying an axisymmetric orbit-superposition code to near-infrared integral field data obtained using adaptive optics with the Gemini NIFS spectrograph .
When our models attempt to fit both the NIFS kinematics and additional low spatial resolution kinematics , our results depend sensitively on how \chi ^ { 2 } is computed — probably a consequence of complex bar kinematics that manifest immediately outside the nuclear region .
The most robust results are obtained when only the high spatial resolution kinematic constraints in the nuclear region are included in the fit .
Our best estimates for the BH mass and H -band mass-to-light ratio are { { \mathrm { M } } _ { BH } } \sim 3.76 \pm 1.15 \times 10 ^ { 7 } ~ { } { { \mathrm { M } } _ { \odot } } ( 1 \sigma error ) and \Upsilon _ { H } \sim 0.34 { \pm 0.03 } ~ { } { { \mathrm { M } } _ { \odot } } / { { \mathrm { L } } _ { \odot } } ( 3 \sigma error ) , respectively ( the quoted errors reflect the model uncertainties ) .
Our BH mass measurement is consistent with estimates from both reverberation mapping ( 3.57 ^ { +0.45 } _ { -0.37 } \times~ { } 10 ^ { 7 } ~ { } { { \mathrm { M } } _ { \odot } } ) and gas kinematics ( 3.0 ^ { +0.75 } _ { -2.2 } \times~ { } 10 ^ { 7 } ~ { } { { \mathrm { M } } _ { \odot } } ; 1 \sigma errors ) , and our best-fit mass-to-light ratio is consistent with the photometric estimate of \Upsilon _ { H } = 0.4 \pm 0.2 ~ { } { { \mathrm { M } } _ { \odot } } / { { \mathrm { L } } _ { \odot } } .
The NIFS kinematics give a central bulge velocity dispersion \sigma _ { c } = 116 \pm 3 { \mathrm { km s ^ { -1 } } } , bringing this object slightly closer to the M _ { BH } - \sigma relation for quiescent galaxies .
Although NGC 4151 is one of only a few Seyfert 1 galaxies in which it is possible to obtain a direct dynamical BH mass measurement — and thus , an independent calibration of the reverberation mapping mass scale — the complex bar kinematics makes it less than ideally suited for this purpose .