216 research outputs found
Open Water Propeller Tests in Four Operating Modes
http://deepblue.lib.umich.edu/bitstream/2027.42/96584/1/39015087358282.pd
The Development of New Wake Survey Techniques at the University of Michigan
http://deepblue.lib.umich.edu/bitstream/2027.42/96585/1/39015087358860.pd
A Stellar Dynamical Measurement of the Black Hole Mass in the Maser Galaxy NGC 4258
We determine the mass of the black hole at the center of the spiral galaxy
NGC 4258 by constructing axisymmetric dynamical models of the galaxy. These
models are constrained by high spatial resolution imaging and long-slit
spectroscopy of the nuclear region obtained with the {\em Hubble Space
Telescope}, complemented by ground-based observations extending to larger
radii. Our best mass estimate is \MBH = (3.3 \pm 0.2) \times 10^7 \MSun for
a distance of 7.28 Mpc (statistical errors only). This is within 15% of
(3.82\pm 0.01) \times 10^7 \MSun, the mass determined from the kinematics of
water masers (rescaled to the same distance) assuming they are in Keplerian
rotation in a warped disk. The construction of accurate dynamical models of NGC
4258 is somewhat compromised by an unresolved active nucleus and color
gradients, the latter caused by variations in the stellar population and/or
obscuring dust. These problems are not present in the other black
hole mass determinations from stellar dynamics that have been published by us
and other groups; thus, the relatively close agreement between the stellar
dynamical mass and the maser mass in NGC 4258 enhances our confidence in the
black hole masses determined in other galaxies from stellar dynamics using
similar methods and data of comparable quality.Comment: 58 pages, submitted to ApJ. Some figures excluded due to size. The
entire paper is at http://www.noao.edu/noao/staff/lauer/nuker_papers.htm
The M-sigma and M-L Relations in Galactic Bulges and Determinations of their Intrinsic Scatter
We derive improved versions of the relations between supermassive black hole
mass (M_BH) and host-galaxy bulge velocity dispersion (sigma) and luminosity
(L) (the M-sigma and M-L relations), based on 49 M_BH measurements and 19 upper
limits. Particular attention is paid to recovery of the intrinsic scatter
(epsilon_0) in both relations. We find log(M_BH / M_sun) = alpha + beta *
log(sigma / 200 km/s) with (alpha, beta, epsilon_0) = (8.12 +/- 0.08, 4.24 +/-
0.41, 0.44 +/- 0.06) for all galaxies and (alpha, beta, epsilon_0) = (8.23 +/-
0.08, 3.96 +/- 0.42, 0.31 +/- 0.06) for ellipticals. The results for
ellipticals are consistent with previous studies, but the intrinsic scatter
recovered for spirals is significantly larger. The scatter inferred reinforces
the need for its consideration when calculating local black hole mass function
based on the M-sigma relation, and further implies that there may be
substantial selection bias in studies of the evolution of the M-sigma relation.
We estimate the M-L relationship as log(M_BH / M_sun) = alpha + beta * log(L_V
/ 10^11 L_sun,V) of (alpha, beta, epsilon_0) = (8.95 +/- 0.11, 1.11 +/- 0.18,
0.38 +/- 0.09); using only early-type galaxies. These results appear to be
insensitive to a wide range of assumptions about the measurement errors and the
distribution of intrinsic scatter. We show that culling the sample according to
the resolution of the black hole's sphere of influence biases the relations to
larger mean masses, larger slopes, and incorrect intrinsic residuals.Comment: 27 pages, 18 figures, 7 tables, ApJ accepte
A Quintet Of Black Hole Mass Determinations
We report five new measurements of central black hole masses based on Space Telescope Imaging Spectrograph and Wide Field Planetary Camera 2 observations with the Hubble Space Telescope (HST) and on axisymmetric, three-integral, Schwarzschild orbit-library kinematic models. We selected a sample of galaxies within a narrow range in velocity dispersion that cover a range of galaxy parameters (including Hubble type and core/power-law surface density profile) where we expected to be able to resolve the galaxy's sphere of influence based on the predicted value of the black hole mass from the M-sigma relation. We find masses for the following galaxies: NGC3585, M(BH) = 3.4(-0.6)(+1.5) x 10(8) M(circle dot;) NGC 3607, M(BH) = 1.2(-0.4)(+0.4) x 10(8) M(circle dot); NGC 4026, M(BH) = 2.1(-0.4)(+0.7) x 10(8) M(circle dot); and NGC 5576, M(BH) = 1.8(-0.4)(+0.3) x 10(8) M(circle dot), all significantly excluding M(BH) = 0. For NGC 3945, M(BH) = 9(-21)(+17) x 10(6) M(circle dot), which is significantly below predictions from M-sigma and M-L relations and consistent with MBH = 0, though the presence of a double bar in this galaxy may present problems for our axisymmetric code.NASA/HST GO-5999, GO-6587, GO-6633, GO-7468, GO-9107NASA NAS 5-26555Astronom
Dwarf Galaxy Dark Matter Density Profiles Inferred from Stellar and Gas Kinematics
We present new constraints on the density profiles of dark matter (DM) halos
in seven nearby dwarf galaxies from measurements of their integrated stellar
light and gas kinematics. The gas kinematics of low mass galaxies frequently
suggest that they contain constant density DM cores, while N-body simulations
instead predict a cuspy profile. We present a data set of high resolution
integral field spectroscopy on seven galaxies and measure the stellar and gas
kinematics simultaneously. Using Jeans modeling on our full sample, we examine
whether gas kinematics in general produce shallower density profiles than are
derived from the stars. Although 2/7 galaxies show some localized differences
in their rotation curves between the two tracers, estimates of the central
logarithmic slope of the DM density profile, gamma, are generally robust. The
mean and standard deviation of the logarithmic slope for the population are
gamma=0.67+/-0.10 when measured in the stars and gamma=0.58+/-0.24 when
measured in the gas. We also find that the halos are not under concentrated at
the radii of half their maximum velocities. Finally, we search for correlations
of the DM density profile with stellar velocity anisotropy and other baryonic
properties. Two popular mechanisms to explain cored DM halos are an exotic DM
component or feedback models that strongly couple the energy of supernovae into
repeatedly driving out gas and dynamically heating the DM halos. We investigate
correlations that may eventually be used to test models. We do not find a
secondary parameter that strongly correlates with the central DM density slope,
but we do find some weak correlations. Determining the importance of these
correlations will require further model developments and larger observational
samples. (Abridged)Comment: 29 pages, 18 figures, 10 tables, accepted for publication in Ap
Is There a Black Hole in NGC 4382?
We present Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph observations of the galaxy NGC 4382 (M85) and axisymmetric models of the galaxy to determine mass-to-light ratio ( ##IMG## [http://ej.iop.org/icons/Entities/Upsi.gif] {Upsilon} V ) and central black hole mass ( M BH ). We find ##IMG## [http://ej.iop.org/icons/Entities/Upsi.gif] {Upsilon} V = 3.74 ± 0.1 M _ / L _ and M BH = 1.3 +5.2 – 1.2 _ 10 7 M _ at an assumed distance of 17.9 Mpc, consistent with no black hole. The upper limit, M BH < 9.6 _ 10 7 M _ (2_) or M BH < 1.4 _ 10 8 (3_), is consistent with the current M -_ relation, which predicts M BH = 8.8 _ 10 7 M _ at _ e = 182 km s –1 , but low for the current M - L relation, which predicts M BH = 7.8 _ 10 8 M _ at L V = 8.9 _ 10 10 L _, V . HST images show the nucleus to be double, suggesting the presence of a nuclear eccentric stellar disk, analogous to the Tremaine disk in M31. This conclusion is supported by the HST velocity dispersion profile. Despite the presence of this non-axisymmetric feature and evidence of a recent merger, we conclude that the reliability of our black hole mass determination is not hindered. The inferred low black hole mass may explain the lack of nuclear activity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90768/1/0004-637X_741_1_38.pd
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 M and the velocity dispersion sigma of the host
galaxy, of the form log(M/M_sun) = a + b*log(sigma/sigma_0); however, published
estimates of the slope b span a wide range (3.75 to 5.3). Merritt & Ferrarese
have argued that low slopes (<4) 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 account for at most a small
part of the slope range. Instead, the range of slopes arises mostly because of
systematic 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
& Merritt's extrapolation of central velocity dispersions to r_e/8 (r_e is the
effective radius) using an empirical formula. Another component may arise from
dispersion-dependent systematic errors in the measurements. A new determination
of the slope using 31 galaxies yields b=4.02 +/- 0.32, a=8.13 +/- 0.06, for
sigma_0=200 km/s. The M-sigma relation has an intrinsic dispersion in log M
that is no larger than 0.3 dex. In an Appendix, we present a simple model for
the velocity-dispersion profile of the Galactic bulge.Comment: 37 pages, 9 figure
The Masses of Nuclear Black Holes in Luminous Elliptical Galaxies and Implications for the Space Density of the Most Massive Black Holes
Black hole masses predicted from the Mbh-sigma relationship conflict with
those predicted from the Mbh-L relationship for the most luminous galaxies,
such as brightest cluster galaxies (BCGs). This is because stellar velocity
dispersion, sigma, increases only weakly with L for BCGs and other giant
ellipticals. The Mbh-L relationship predicts that the most luminous BCGs may
have Mbh approaching 10^{10}M_sol, while the M-sigma relationship always
predicts Mbh<3X10^9M_sol. We argue that the Mbh-L relationship is a plausible
or even preferred description for BCGs and other galaxies of similar
luminosity. If cores in central stellar density are formed by binary BHs, then
the inner-core cusp radius, r_gamma, may be an independent witness of Mbh.
Using structural parameters derived from a large sample of early-type galaxies
observed by HST, we argue that L is superior to sigma as an indicator of
r_gamma in luminous galaxies. The observed r_gamma-Mbh relationship for 11 core
galaxies with measured Mbh appears to be consistent with the Mbh-L relationship
for BCGs. BCGs have large cores appropriate for their large luminosities that
may be difficult to generate with the modest BH masses inferred from the
Mbh-sigma relationship. Mbh~L may be expected to hold for BCGs, if they were
formed in dissipationless mergers, which should preserve ratio of BH to stellar
mass. This picture appears to be consistent with the slow increase in sigma
with L and the more rapid increase in effective radii with L seen in BCGs. If
BCGs have large BHs commensurate with their luminosities, then the local BH
mass function for Mbh>3X10^9M_sol may be nearly an order of magnitude richer
than that inferred from the Mbh-sigma relationship. The volume density of QSOs
at earlier epochs may favor the predictions from the Mbh-L relationship.Comment: 62 pages, 18 figures, submitted to the Astrophysical Journal; revised
after initial revie
The Demography of Massive Dark Objects in Galaxy Centres
We construct dynamical models for a sample of 36 nearby galaxies with Hubble
Space Telescope 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
Upsilon, and a central massive dark object (MDO) of arbitrary mass M_bh. They
provide acceptable fits to 32 of the galaxies for some value of M_bh and
Upsilon; the four galaxies that cannot be fit have kinematically decoupled
cores. The mass-to-light ratios inferred for the 32 well-fit galaxies are
consistent with the fundamental plane correlation Upsilon \propto L^0.2, where
L is galaxy luminosity. In all but six galaxies the models require at the 95%
confidence level an MDO of mass M_bh ~ 0.006 M_bulge = 0.006 Upsilon L. Five of
the six galaxies consistent with M_bh=0 are also consistent with this
correlation. The other (NGC 7332) has a much stronger upper limit on M_bh. 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 galaxies have
MDOs, whose masses are well described by a Gaussian distribution in log
(M_bh/M_bulge) of mean -2.27 and width ~0.07.Comment: 28 pages including 13 figures and 4 tables. Submitted to A
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