98 research outputs found
A Theoretical Model for the Relation for Supermassive Black Holes in Galaxies
We construct a model for the formation of black holes within galactic bulges.
The initial state is a slowly rotating isothermal sphere, characterized by
effective transport speed \aeff and rotation rate . The black hole
mass is determined when the centrifugal radius of the collapse flow exceeds the
capture radius of the central black hole. This model reproduces the observed
correlation between black hole masses and galactic velocity dispersions, \mbh
\approx 10^8 M_\odot (\sigma/200 \kms)^4, where \sigma = \sqrt{2} \aeff.
This model also predicts the ratio \mrat of black hole mass to host mass:
\mrat 0.004 (\sigma/200 \kms).Comment: 9 pages, 2 figures, submitted to Astrophysical Journal Letter
The Cosmological Dependence of Cluster Density Profiles
We use N-body simulations to study the shape of mean cluster density and
velocity profiles formed via gravitational instability. The dependence of the
final structure on both cosmology and initial density field is examined, using
a grid of cosmologies and scale-free initial power spectra P\propto k^n. For
each model, we stack clusters to define an average density profile in the
non-linear regime. The profiles are well fit by a power law over 99% of the
cluster volume, with a clear trend toward steeper slopes with both increasing n
and decreasing Omega_o. For models with a Omega_o = 0.2, the profile slopes are
consistently higher than those for Omega-1.0. Cluster density profiles are thus
potentially useful cosmological diagnostics. We find no evidence for a constant
density core in any of the models, although the density profiles do tend to
flatten at small radii. Much of the flattening is due to the force softening
required by the simulations, and an attempt is made to recover the unsoftened
profiles assuming angular momentum invariance. The recovered profiles in the
Omega=1 cosmologies are consistent with a pure power law up to the highest
density contrasts (10^6) accessible with our resolution. The low density models
show significant deviations from a power law above density contrasts \sim 10^5.
We interpret this curvature as reflecting the non scale-invariant nature of the
background cosmology in these models.Comment: uuencoded, 22 pages + 13 figs. Astrophysical Journal, in pres
The Black Hole in the Compact, High-dispersion Galaxy NGC 1271
Located in the Perseus cluster, NGC 1271 is an early-type galaxy with a small
effective radius of 2.2 kpc and a large stellar velocity dispersion of 276 km/s
for its K-band luminosity of 8.9x10^{10} L_sun. We present a mass measurement
for the black hole in this compact, high-dispersion galaxy using observations
from the integral field spectrograph NIFS on the Gemini North telescope
assisted by laser guide star adaptive optics, large-scale integral field unit
observations with PPAK at the Calar Alto Observatory, and Hubble Space
Telescope WFC3 imaging observations. We are able to map out the stellar
kinematics on small spatial scales, within the black hole sphere of influence,
and on large scales that extend out to four times the galaxy's effective
radius. We find that the galaxy is rapidly rotating and exhibits a sharp rise
in the velocity dispersion. Through the use of orbit-based stellar dynamical
models, we determine that the black hole has a mass of (3.0^{+1.0}_{-1.1}) x
10^9 M_sun and the H-band stellar mass-to-light ratio is 1.40^{+0.13}_{-0.11}
M_sun/L_sun (1-sigma uncertainties). NGC 1271 occupies the sparsely-populated
upper end of the black hole mass distribution, but is very different from the
Brightest Cluster Galaxies (BCGs) and giant elliptical galaxies that are
expected to host the most massive black holes. Interestingly, the black hole
mass is an order of magnitude larger than expectations based on the galaxy's
bulge luminosity, but is consistent with the mass predicted using the galaxy's
bulge stellar velocity dispersion. More compact, high-dispersion galaxies need
to be studied using high spatial resolution observations to securely determine
black hole masses, as there could be systematic differences in the black hole
scaling relations between these types of galaxies and the BCGs/giant
ellipticals, thereby implying different pathways for black hole and galaxy
growth.Comment: accepted for publication in Ap
The Centers of Early-Type Galaxies with HST III: Non-Parametric Recovery of Stellar Luminosity Distributions
We have non-parametrically determined the luminosity density profiles and
their logarithmic slopes for 42 early-type galaxies observed with HST. Assuming
that the isodensity contours are spheroidal, then the luminosity density is
uniquely determined from the surface brightness data through the Abel equation.
For nearly all the galaxies in our sample, the logarithmic slope of the
luminosity density measured at 0.1" (the innermost reliable measurement with
the uncorrected HST) is significantly different from zero; i.e. most elliptical
galaxies have cusps. There are only two galaxies for which an analytic core
cannot be excluded. The distribution of logarithmic slopes at 0.1" appears to
be bimodal, confirming the conclusion of Lauer et al. (1995) that early-type
galaxies can be divided into two types based on their surface-brightness
profiles; i.e., those with cuspy cores and those whose steep power-law profiles
continue essentially unchanged in to the resolution limit. The peaks in the
slope distribution occur at -0.8 and -1.9. More than half of the galaxies have
slopes steeper than -1.0. Taken together with the recent theoretical work of
Merritt & Fridman, these results suggest that many (and maybe most) elliptical
galaxies are either nearly axisymmetric or spherical near the center, or slowly
evolve due to the influence of stochastic orbits.Comment: uuencoded compressed tarfile 21 pages with 6 fig, 1 tabl
Probing Stellar Dynamics in Galactic Nuclei
Electromagnetic observations over the last 15 years have yielded a growing
appreciation for the importance of supermassive black holes (SMBH) to the
evolution of galaxies, and for the intricacies of dynamical interactions in our
own Galactic center. Here we show that future low-frequency gravitational wave
observations, alone or in combination with electromagnetic data, will open up
unique windows to these processes. In particular, gravitational wave detections
in the 10^{-5}-10^{-1} Hz range will yield SMBH masses and spins to
unprecedented precision and will provide clues to the properties of the
otherwise undetectable stellar remnants expected to populate the centers of
galaxies. Such observations are therefore keys to understanding the interplay
between SMBHs and their environments.Comment: 8 pages, Science white paper for the Astro2010 Decadal Surve
A \u3cem\u3eChandra\u3c/em\u3e Survey of Supermassive Black Holes with Dynamical Mass Measurements
We present Chandra observations of 12 galaxies that contain supermassive black holes (SMBHs) with dynamical mass measurements. Each galaxy was observed for 30 ks and resulted in a total of 68 point-source detections in the target galaxies including SMBH sources, ultraluminous X-ray sources (ULXs), and extragalactic X-ray binaries. Based on our fits of the X-ray spectra, we report fluxes, luminosities, Eddington ratios, and slope of the power-law spectrum. Normalized to the Eddington luminosity, the 2-10 keV band X-ray luminosities of the SMBH sources range from 10-8 to 10-6, and the power-law slopes are centered at ~2 with a slight trend toward steeper (softer) slopes at smaller Eddington fractions, implying a change in the physical processes responsible for their emission at low accretion rates. We find 20 ULX candidates, of which 6 are likely (\u3e90% chance) to be true ULXs. The most promising ULX candidate has an isotropic luminosity in the 0.3-10 keV band of 1.0+0.6 - 0.3 × 1040 erg s-1
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