The Black Hole Mass of NGC 4151. II. Stellar Dynamical Measurement from
  Near-Infrared Integral Field Spectroscopy
  We present a revised measurement of the mass of the central black hole (Mbh)
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-squared 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 Mbh~(3.76+/-1.15)E7 Msun (1-sigma error) and
M/L(H-band)~0.34+/-0.03 Msun/Lsun (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]E7 Msun) and
gas kinematics (3.0[+0.75/-2.2]E7 Msun; 1-sigma errors), and our best-fit
mass-to-light ratio is consistent with the photometric estimate of
M/L(H-band)=0.4+/-0.2 Msun/Lsun. The NIFS kinematics give a central bulge
velocity dispersion sigma_c=116+/-3 km/s, bringing this object slightly closer
to the M-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.
