458 research outputs found
The black hole mass versus velocity dispersion relation in QSOs/Active Galactic Nuclei: observational appearance and black hole growth
Studies of massive black holes (BHs) in nearby galactic centers have revealed
a tight correlation between BH mass and galactic velocity dispersion. In this
paper we investigate how the BH mass versus velocity dispersion relation and
the nuclear luminosity versus velocity dispersion relation in QSOs/active
galactic nuclei (AGNs) are connected with the BH mass versus velocity
dispersion relation in local galaxies, through the nuclear luminosity evolution
of individual QSOs/AGNs and the mass growth of individual BHs. In the study we
ignore the effects of BH mergers and assume that the velocity dispersion does
not change significantly during and after the nuclear activity phase. Using the
observed correlation in local galaxies and an assumed form of the QSO/AGN
luminosity evolution and BH growth, we obtain the simulated observational
appearance of the BH mass versus velocity dispersion relation in QSOs/AGNs. The
simulation results illustrate how the BH accretion history (e.g., the lifetime
of nuclear activity and the possibility that QSOs/AGNs accrete at a
super-Eddington accretion rate at the early evolutionary stage) can be inferred
from the difference between the relation in QSOs/AGNs and that in local
galaxies. We also show how the difference may be weakened by the flux limit of
telescopes. We expect that a large complete sample of QSOs/AGNs with accurate
BH mass and velocity dispersion measurements will help to quantitatively
constrain QSO/AGN luminosity evolution and BH growth models.Comment: 20 pages, including 4 figures; revised to match the published versio
General Relativistic Magnetohydrodynamic Simulations of Black Hole Accretion Disks: Results and Observational Implications
A selection of results from the general relativistic MHD accretion
simulations described in the previous talk are presented. We find that the
magnetic field strength increases sharply with decreasing radius and is also
enhanced near rapidly-spinning black holes. The greater magnetic field strength
associated with rapid black hole rotation leads to a large outward
electromagnetic angular momentum flux that substantially reduces both the mean
accretion rate and the net accreted angular momentum per unit rest-mass. This
electromagnetic stress strongly violates the traditional guess that the
accretion stress vanishes at and inside the marginally stable orbit. Possible
observational consequences include a constraint on the maximum spin of black
holes, enhancement to the radiative efficiency, and concentration of
fluorescent Fe Kalpha to the innermost part of the accretion disk.Comment: invited review at the conference "Stellar-mass, Intermediate-mass,
and Supermassive Black Holes", held in Kyoto, Japan, Octorber 28-31, 2003, to
be published in Progress of Theoretical Physics Supplemen
Inclinations and black hole masses of Seyfert 1 galaxies
A tight correlation of black hole mass and central velocity dispersion has
been found recently for both active and quiescent galaxies. By applying this
correlation, we develop a simple method to derive the inclination angles for a
sample of 11 Seyfert 1 galaxies that have both measured central velocity
dispersions and black hole masses estimated by reverberation mapping. These
angles, with a mean value of 36 degree that agrees well with the result
obtained by fitting the iron K lines of Seyfert 1s observed with ASCA,
provide further support to the orientation-dependent unification scheme of AGN.
A positive correlation of the inclinations with observed FWHMs of H line
and a possible anti-correlation with the nuclear radio-loudness have been
found. We conclude that more accurate knowledge on inclinations and broad line
region dynamics is needed to improve the black hole mass determination of AGN
with the reverberation mapping technique.Comment: 12 pages including 4 figures, accepted for publication in The
Astrophysical Journal Letter
On The Linearity of The Black Hole - Bulge Mass Relation in Active and in Nearby Galaxies
Analysis of PG quasar observations suggests a nonlinear relation between the
black hole mass, M_BH, and the bulge mass, M_bulge, although a linear relation,
as proposed for nearby galaxies, cannot be ruled out. New M_BH values for
nearby galaxies from Gebhardt et al., and L_bulge measurements for Seyfert 1
galaxies from Virani et al., are used here to obtain a more accurate value for
the slope of the M_BH-M_bulge relation. The combined sample of 40 active and
non-active galaxies suggests a significantly nonlinear relation, M_BH\propto
M_bulge^{1.53\pm 0.14}. Further support for a nonlinear relation is provided by
the slope of the M_BH-stellar velocity dispersion relation found recently, and
by the low M_BH found in late type spiral galaxies. The mean M_BH/M_bulge ratio
is therefore not a universal constant, but rather drops from ~0.5% in bright
(M_V ~ -22) ellipticals, to ~0.05% in low luminosity (M_V ~ -18) bulges. Hubble
Space Telescope determinations of M_BH in late type spirals, and of the bulge
magnitude in narrow line Seyfert 1 galaxies (both predicted to have low M_BH),
can further test the validity of the nonlinear M_BH-M_bulge relation.Comment: Accepted for publication in ApJ, 9 pages inc. 2 figure
AGN Obscuring Tori Supported by Infrared Radiation Pressure
Explicit 2-d axisymmetric solutions are found to the hydrostatic equilibrium,
energy balance, and photon diffusion equations within obscuring tori around
active galactic nuclei. These solutions demonstrate that infrared radiation
pressure can support geometrically thick structures in AGN environments subject
to certain constraints: the bolometric luminosity must be roughly 0.03--1 times
the Eddington luminosity; and the Compton optical depth of matter in the
equatorial plane should be order unity, with a tolerance of about an order of
magnitude up or down. Both of these constraints are at least roughly consistent
with observations. In addition, angular momentum must be redistributed so that
the fractional rotational support against gravity rises from the inner edge of
the torus to the outer in a manner specific to the detailed shape of the
gravitational potential. This model also predicts that the column densities
observed in obscured AGN should range from about 10^{22} to about 10^{24}
cm^{-2}.Comment: ApJ, in pres
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