We present a stellar dynamical estimate of the black hole (BH) mass in the Seyfert 1 galaxy, NGC 4151. We analyze ground-based spectroscopy as well as imaging data from the ground and space, and we ...construct three-integral axlsymmetric models in order to constrain the BH mass and mass-to-light ratio. The dynamical models depend on the assumed inclination of the kinematic symmetry axis of the stellar bulge. In the case in which the bulge is assumed to be viewed edge-on, the kinematical data give only an upper limit to the mass of the BH, of similar to 4 x 10 super(7) M unk (1 sigma ). If the bulge kinematic axis is assumed to have the same inclination as the symmetry axis of the large-scale galaxy disk (i.e., 23 degree relative to the line of sight), a best-fit dynamical mass between 4 and 5 x 10 super(7) M unk is obtained. However, because of the poor quality of the fit when the bulge is assumed to be inclined (as determined by the noisiness of the chi super(2) surface and its minimum value) and because we lack spectroscopic data that clearly resolves the BH sphere of influence, we consider our measurements to be tentative estimates of the dynamical BH mass. With this preliminary result, NGC 4151 is now among the small sample of galaxies in which the BH mass has been constrained from two independent techniques, and the mass values we find for both bulge inclinations are in reasonable agreement with the recent estimate from reverberation mapping (4.57 super(+) sub(-) super(0) sub(0) super(.) sub(.) super(5) sub(4) super(7) sub(7) x 10 super(7) M unk, published by Bentz et al.
We construct dynamical models for a sample of 36 nearby galaxies with HST photometry and ground-based kinematics. The models assume that each galaxy is axisymmetric, with a two-integral distribution ...function, arbitrary inclination angle, a position-independent stellar mass-to-light ratio , and a central massive dark object (MDO) of arbitrary mass. They provide acceptable fits to 32 of the galaxies for some arbitrary-mass value and Upsilon; the four galaxies that cannot be fitted have kinematically decoupled cores. The mass-to-light ratios inferred for the 32 well-fitted galaxies are consistent with the fundamental-plane correlation Upsilon varies as L exp 0.2, where L is galaxy luminosity. We predict the second-moment profiles that should be observed at HST resolution for the 32 galaxies that our models describe well. We consider various parameterizations for the probability distribution describing the correlation of the masses of these MDOs with other galaxy properties. (Author)
Black hole masses in active galactic nuclei are difficult to measure using conventional dynamical methods but can be determined using the technique of reverberation mapping. However, it is important ...to verify that the results of these different methods are equivalent. This can be done indirectly, using scaling relations between the black hole and the host galaxy spheroid. For this purpose, we have obtained new measurements of the bulge stellar velocity dispersion, sigma *, in Seyfert 1 galaxies. These are used in conjunction with the M sub(BH)- sigma * relation to validate nuclear black hole masses, M sub(BH), in active galaxies determined through reverberation mapping. We find that Seyfert galaxies follow the same M sub(BH)- sigma * relation as nonactive galaxies, indicating that reverberation mapping measurements of M sub(BH) are consistent with those obtained using other methods. We also reconsider the relationship between bulge absolute magnitude, M sub(bul), and black hole mass. We find that Seyfert galaxies are offset from nonactive galaxies, but that the deviation can be entirely understood as a difference in bulge luminosity, not black hole mass; Seyfert galaxy hosts are brighter than normal galaxies for a given value of their velocity dispersion, perhaps as a result of younger stellar populations.
We present Hubble Space Telescope (HST) spectroscopy of the nucleus of M31 obtained with the Space Telescope Imaging Spectrograph (STIS). Spectra that include the Ca II infrared triplet (l 8500 Ae) ...see only the red giant stars in the double brightness peaks P1 and P2. In contrast, spectra taken at l 3600-5100 Ae are sensitive to the tiny blue nucleus embedded in P2, the lower surface brightness nucleus of the galaxy. P2 has a K-type spectrum, but we find that the blue nucleus has an A-type spectrum: it shows strong Balmer absorption lines. Hence, the blue nucleus is blue not because of AGN light but rather because it is dominated by hot stars. We show that the spectrum is well described by A0 giant stars, A0 dwarf stars, or a 200 Myr old, single-burst stellar population. White dwarfs, in contrast, cannot fit the blue nucleus spectrum. Given the small likelihood for stellar collisions, recent star formation appears to be the most plausible origin of the blue nucleus. In stellar population, size, and velocity dispersion, the blue nucleus is so different from P1 and P2 that we call it P3 and refer to the nucleus of M31 as triple. Because P2 and P3 have very different spectra, we can make a clean decomposition of the red and blue stars and hence measure the light distribution and kinematics of each uncontaminated by the other. The line-of-sight velocity distributions of the red stars near P2 strengthen the support for Tremaine's eccentric disk model. Their wings indicate the presence of stars with velocities of up to 1000 km s super(-1) on the anti-P1 side of P2. The kinematics of P3 are consistent with a circular stellar disk in Keplerian rotation around a supermassive black hole. If the P3 disk is perfectly thin, then the inclination angle i 55 is identical within the errors to the inclination of the eccentric disk models for P1+P2 by Peiris & Tremaine and by Salow & Statler. Both disks rotate in the same sense and are almost coplanar. The observed velocity dispersion of P3 is largely caused by blurred rotation and has a maximum value of s = 1183 c 201 km s super(-1). This is much larger than the dispersion s 250 km s super(-1) of the red stars along the same line of sight and is the largest integrated velocity dispersion observed in any galaxy. The rotation curve of P3 is symmetric around its center. It reaches an observed velocity of V = 618 c 81 km s super(-1) at radius 0.05 = 0.19 pc, where the observed velocity dispersion is s = 674 c 95 km s super(-1). The corresponding circular rotation velocity at this radius is 61700 km s super(-1). We therefore confirm earlier suggestions that the central dark object interpreted as a supermassive black hole is located in P3. Thin-disk and Schwarzschild models with intrinsic axial ratios b/a < 0.26 corresponding to inclinations between 55 and 58 match the P3 observations very well. Among these models, the best fit and the lowest black hole mass are obtained for a thin-disk model with sub(; ) = 1.4 x 10 super(8) M sub(z). Allowing P3 to have some intrinsic thickness and considering possible systematic errors, the 1 s confidence range becomes (1.1-2.3) x 10 super(8) M sub(z). The black hole mass determined from P3 is independent of but consistent with Peiris & Tremaine's mass estimate based on the eccentric disk model for P1+P2. It is 62 times larger than the prediction by the correlation between M sub(; ) and bulge velocity dispersion s sub(bulge). Taken together with other reliable black hole mass determinations in nearby galaxies, notably the Milky Way and M32, this strengthens the evidence that the M sub(; )-s sub(bulge) relation has significant intrinsic scatter, at least at low black hole masses. We show that any dark star cluster alternative to a black hole must have a half-mass radius <0.03 = 0.11 pc in order to match the observations. Based on this, M31 becomes the third galaxy (after NGC 4258 and our Galaxy) in which clusters of brown dwarf stars or dead stars can be excluded on astrophysical grounds.
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