Gary Allen Bower

The Demography of Massive Dark Objects in Galaxy Centers

We construct dynamical models for a sample of 36 nearby galaxies with Hubble Space Telescope (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 M•. They provide acceptable fits to 32 of the galaxies for some value of M• and ; 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 ∝ L0.2, where L is galaxy luminosity. In all but six galaxies the models require at the 95% confidence level an MDO of mass M• ~ 0.006Mbulge ≡ 0.006L. Five of the six galaxies consistent with M• = 0 are also consistent with this correlation. The other (NGC 7332) has a much stronger upper limit on M•. 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. One of the best models can be summarized thus: a fraction f 0.97 of early-type galaxies have MDOs, whose masses are well described by a Gaussian distribution in log (M•/Mbulge) of mean -2.28 and standard deviation ~0.51. There is also marginal evidence that M• is distributed differently for core and power law galaxies, with core galaxies having a somewhat steeper dependence on Mbulge.

A Relationship between nuclear black hole mass and galaxy velocity dispersion

We describe a correlation between the mass Mbh of a galaxys central black hole and the luminosity-weighted line-of-sight velocity dispersion σe within the half-light radius. The result is based on a sample of 26 galaxies, including 13 galaxies with new determinations of black hole masses from Hubble Space Telescope measurements of stellar kinematics. The best-fit correlation is Mbh = 1.2(±0.2) × 108 M☉(σe/200 km s-1)3.75 (±0.3) over almost 3 orders of magnitude in Mbh; the scatter in Mbh at fixed σe is only 0.30 dex, and most of this is due to observational errors. The Mbh-σe relation is of interest not only for its strong predictive power but also because it implies that central black hole mass is constrained by and closely related to properties of the host galaxys bulge.

THE SLOPE OF THE BLACK HOLE MASS VERSUS VELOCITY DISPERSION CORRELATION

Observations of nearby galaxies reveal a strong correlation between the mass of the central dark object MBH and the velocity dispersionof the host galaxy, of the form logðMBH=M� Þ¼ � þ � logð�=� 0Þ; how- ever, published estimates of the slopespan a wide range (3.75-5.3). Merritt & Ferrarese have argued that low slopes (d4) arise because of neglect of random measurement errors in the dispersions and an incorrect choice for the dispersion of the Milky Way Galaxy. We show that these explanations and several others account for at most a small part of the slope range. Instead, the range of slopes arises mostly because of sys- tematic differences in the velocity dispersions used by different groups for the same galaxies. The origin of these differences remains unclear, but we suggest that one significant component of the difference results from Ferrarese & Merritts extrapolation of central velocity dispersions to re= 8( re is the effective radius) using an empirical formula. Another component may arise from dispersion-dependent systematic errors in the mea- surements. A new determination of the slope using 31 galaxies yields � ¼ 4:02 � 0:32, � ¼ 8:13 � 0:06 for � 0 ¼ 200 km s � 1 . The MBH-� relation has an intrinsic dispersion in log MBH that is no larger than 0.25-0.3 dex and may be smaller if observational errors have been underestimated. In an appendix, we present a simple kinematic model for the velocity-dispersion profile of the Galactic bulge. Subject headings: black hole physics — galaxies: bulges — galaxies: fundamental parameters — galaxies: nuclei — Galaxy: bulge — Galaxy: kinematics and dynamics

Black Hole Mass Estimates from Reverberation Mapping and from Spatially Resolved Kinematics

Black hole (BH) masses that have been measured by reverberation mapping in active galaxies fall significantly below the correlation between bulge luminosity and BH mass determined from spatially resolved kinematics of nearby normal galaxies. This discrepancy has created concern that one or both techniques suffer from systematic errors. We show that BH masses from reverberation mapping are consistent with the recently discovered relationship between BH mass and galaxy velocity dispersion. Therefore, the bulge luminosities are the probable source of the disagreement, not problems with either method of mass measurement. This result underscores the utility of the BH mass-velocity dispersion relationship. Reverberation mapping can now be applied with increased confidence to galaxies whose active nuclei are too bright or whose distances are too large for BH searches based on spatially resolved kinematics.

Axisymmetric Dynamical Models of the Central Regions of Galaxies

We present axisymmetric, orbit superposition models for 12 galaxies using data taken with the Hubble Space Telescope (HST) and ground-based observatories. In each galaxy, we detect a central black hole (BH) and measure its mass to accuracies ranging from 10% to 70%. We demonstrate that in most cases the BH detection requires both the HST and ground-based data. Using the ground-based data alone does provide an unbiased measure of the BH mass (provided that they are fitted with fully general models), but at a greatly reduced significance. The most significant correlation with host galaxy properties is the relation between the BH mass and the velocity dispersion of the host galaxy; we find no other equally strong correlation and no second parameter that improves the quality of the mass-dispersion relation. We are also able to measure the stellar orbital properties from these general models. The most massive galaxies are strongly biased to tangential orbits near the BH, consistent with binary BH models, while lower mass galaxies have a range of anisotropies, consistent with an adiabatic growth of the BH. Subject headings: black hole physics — galaxies: general — galaxies: nuclei — galaxies: statistics — stellar dynamics On-line material: color figures

HST STIS spectroscopy of the triple nucleus of M31: two nested disks in keplerian rotation around a supermassive black hole

We present Hubble Space Telescope (HST) spectroscopy of the nucleus of M31 obtained with the Space TelescopeImagingSpectrograph(STIS).SpectrathatincludetheCaiiinfraredtriplet(k ’ 85008)seeonlythered giant stars in the double brightness peaks P1 and P2. In contrast, spectra taken atk ’ 3600 51008 are sensitive to thetinybluenucleusembeddedinP2,thelowersurfacebrightnessnucleusofthegalaxy.P2 hasaK-typespectrum, 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 eachuncontaminated 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 � 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 diskis perfectlythin,thentheinclination anglei ’ 55 � isidentical withinthe errorsto theinclination 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 � ¼ 1183 � 201 km s � 1 . This is much larger than the dispersion � ’ 250 km s � 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 ¼ 618 � 81 km s � 1 at radius 0B05 ¼ 0:19 pc, where the observed velocity dispersion is � ¼ 674 � 95 km s � 1 . The corresponding circular rotation velocity at this radius is � 1700 km s � 1 . We therefore confirm earlier suggestions that the central dark object

M33: A Galaxy with No Supermassive Black Hole

Galaxies that contain bulges appear to contain central black holes whose masses correlate with the velocity dispersion of the bulge. We show that no corresponding relationship applies in the pure disk galaxy M33. Three-integral dynamical models fit Hubble Space Telescope WFPC2 photometry and Space Telescope Imaging Spectrograph spectroscopy best if the central black hole mass is zero. The upper limit is 1500 M⊙. This is significantly below the mass expected from the velocity dispersion of the nucleus and far below any mass predicted from the disk kinematics. Our results suggest that supermassive black holes are associated only with galaxy bulges and not with their disks.

The Relationship Between Black Hole Mass and Velocity Dispersion in Seyfert 1 Galaxies

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, σ*, in Seyfert 1 galaxies. These are used in conjunction with the MBH-σ* relation to validate nuclear black hole masses, MBH, in active galaxies determined through reverberation mapping. We find that Seyfert galaxies follow the same MBH-σ* relation as nonactive galaxies, indicating that reverberation mapping measurements of MBH are consistent with those obtained using other methods. We also reconsider the relationship between bulge absolute magnitude, Mbul, 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.

Kinematics of 10 Early-Type Galaxies from Hubble Space Telescope and Ground-based Spectroscopy*

We present stellar kinematics for a sample of 10 early-type galaxies observed using the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope, and the Modular Spectrograph on the MDM Observatory 2.4-m telescope. These observations are a part of an ongoing program to understand the co-evolution of supermassive black holes and their host galaxies. Our spectral ranges include either the calcium triplet absorption lines at 8498, 8542, and 8662 A, or the Mg b absorption at 5175 A. The lines are used to derive line-of-sight velocity distributions (LOSVDs) of the stars using a Maximum Penalized Likelihood method. We use Gauss-Hermite polynomials to parameterize the LOSVDs and find predominant ly negative h4 values (boxy distributions) in the central regions of our galaxies. One galaxy, NGC 4697, has significantly positive central h4 (high tail weight). The majority of galaxies have a central velocity dispersion excess in the STIS kinematics over ground-based velocity dispersions. The galaxies with the strongest rotational su pport, as quantified with vMAX/σST IS, have the smallest dispersion excess at STIS resolution. The best-fitting, general, axisymmetric dynamical models ( described in a companion paper) require black holes in all cases, with masses ranging from 10 6.5 to 10 9.3 M⊙. We replot these updated masses on the Mbh - σ relation, and show that the fit to only these 10 galaxies has a slope consi stent with the fits to larger samples. The greatest outlier is NGC 2778, a dwarf elliptical with relatively poor ly constrained black hole mass. The two best candidates for pseudobulges, NGC 3384 and 7457, do not deviate significa ntly from the established relation between Mbh and σ. Neither do the three galaxies which show the most evidence of a recent merger, NGC 3608, 4473, and 4697. Subject headings: galaxies: elliptical and lenticular, cD — galaxies: kinema tics and dynamics

Kinematics of the Nuclear Ionized Gas in the Radio Galaxy M84 (NGC 4374)

We present optical long-slit spectroscopy of the nucleus of the nearby radio galaxy M84 (NGC 4374 = 3C 272.1) obtained with the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope. Our spectra reveal that the nuclear gas disk seen in the Wide Field Planetary Camera 2 imaging by Bower et al. is rotating rapidly. The velocity curve has an S-shape with a peak amplitude of 400 km s−1 at 01 = 8 pc from the nucleus. To model the observed gas kinematics, we construct a thin Keplerian disk model that fits the data well if the rotation axis of the gas disk is aligned with the radio jet axis. These models indicate that the gasdynamics are driven by a nuclear compact mass of 1.5 × 109 M☉ with an uncertainty range of (0.9-2.6) × 109 M☉, and that the inclination of the disk with respect to the plane of the sky is 75°-85°. Of this nuclear mass, only ≤2 × 107 M☉ can possibly be attributed to luminous mass. Thus, we conclude that a dark compact mass (most likely a supermassive black hole) resides in the nucleus of M84.