The black hole mass of NGC 4151. II. Stellar dynamical measurement from near-infrared field spectroscopy

Abstract

We present a revised measurement of themass of the central black hole (MBH ) in the Seyfert 1 galaxyNGC4151. The new stellar dynamical mass measurement is derived by applying an axisymmetric orbit-superposition code to nearinfrared integral field data obtained using adaptive optics with the Gemini Near-infrared Integral Field Spectrograph (NIFS).When our models attempt to fit both the NIFS kinematics and additional low spatial resolution kinematics, our results depend sensitively on how χ2 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 black holemass and H-band mass-to-light ratio are MBH ∼ 3.76±1.15 × 107 M (1σ error) and ϒH ∼ 0.34±0.03 M /L (3σ error), respectively (the quoted errors reflect themodel uncertainties). Our black holemassmeasurement is consistent with estimates from both reverberation mapping (3.57+0.45 −0.37 × 107 M ) and gas kinematics (3.0+0.75 −2.2 × 107 M ; 1σ errors), and our best-fit mass-to-light ratio is consistent with the photometric estimate of ϒH = 0.4 ± 0.2 M /L . The NIFS kinematics give a central bulge velocity dispersion σc = 116 ± 3 kms−1, bringing this object slightly closer to the MBH–σ 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 black hole 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.