Why Massive Black Holes

1
Why Massive Black Holes are
Small in Disk Galaxies ?
Nozomu KAWAKATU Center for Computational Physics,
University of Tsukuba
Collaborator
Masayuki UMEMURA
Center for Computational Physics, University of
Tsukuba
Formation of the First Generation of Galaxies
Strategy for the Observational Corroboration of
Physical Scenarios, 2-5 December 2003, Niigata
University, Niigata, Japan
2
Contents
Introduction
Recent observational results ( BH mass-to-bulge
mass correlation )
Angular momentum transfer problem for
supermassive black holes
Physical mechanism for formation of
Supermassive Black Holes
Radiation drag (Poynting-Robertson) effect
Basic Equation
Equation of angular momentum transfer
Treatment for extinction by dusty gas
Model for Disk galaxies
Results
Relationship between the final BH mass and
bulge-to-disk ratio of host galaxy
Summary
3
Introduction
Recent high quality observations of galactic
centers
2) BH mass-to-galaxy mass ratio is reduced by
more than an order of magnitude with a smaller
bulge-to-disk ratio.
10-2

Normal spiral and barred galaxies
?
Sy2
Sy1
NLSy1
10-3
MBH / Mgalaxy
10-4
10-5
0.1
1
0.03
4
3) BH mass-to-bulge mass ratio lies at a level of
0.001,
which is similar to that found in elliptical
galaxies.
(e.g., Kormendy Richstone 1995)
10-2
10-3
MBH / Mbulge
10-4

Normal spiral and barred galaxies
10-5
Sy1
?
Sy2
NLSy1
1
0.03
0.1
5
Summary of observational results in galactic
centers
Elliptical Galaxies
Disk Galaxies
6
SMBH Formation Angular Momentum Problem
The physics on the angular momentum transfer is
essential !
7
Radiation Drag Poynting-Robertson Effect
Lab.Frame
lt Absorption process gt
In practice, optically thin surface layer is
stripped by radiation drag, and loses angular
momentum (Sato-san talks in details).
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Radiation Drag efficiency in galactic bulges
Optically thick regime
Radiation drag efficiency is determined by the
total number of photons
total luminosity of the bulge
1) The BH-to-bulge mass ratio is basically
determined by the energy conversion efficiency of
nuclear fusion from hydrogen to helium, i.e.,
0.007.
(Umemura 2001)
2) The inhomogeneity of ISM helps the radiation
drag to sustain the maximal efficiency.
(Kawakatu Umemura 2002 )
covering factor O(1)
ISM is observed to highly inhomogeneous in active
star-forming galaxies !
3) By incorporating the realistic chemical
evolution, we predicted
.
(Kawakatu, Umemura Mori 2003 )
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Radiation drag - Geometrical Dilution -
(Umemura et al. 1997,1998 Ohsuga et al. 1999)
Spherical System
Disk-like System
low drag efficiency
high drag efficiency
However, the details are not clear quantitatively
!
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This Work
We investigate the efficiency of radiation drag
in disk galaxies.
We solve the 3D radiation transfer in an
inhomogeneous ISM.
To investigate the relation between the
morphology of host galaxies and the angular
momentum transfer efficiency due to the radiation
drag
We have disclosed the physical reasons
why the BHs are smaller in disk
galaxies!
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Model
1
The difference of morphology is expressed by
changing bulge fraction (fbulge) .
fbulge
0.5
Inhomogeneous ISM
covering factor is unity.
0.03
disk scale height
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Basic Equations
The Eq.of Ang.Mom.Transfer
mass extinction due to dust opacity
radiation energy density
radiation flux
radiation stress tensor
The gain and loss of total angular momentum is
regulated by this equation.
The contribution of the radiation from distant
stars is essential to radiation drag
since these stars have different velocities from
absorbing clouds.
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Treatment of the radiation tranfser
All radiative quantities are determined by
radiation from stars diluted by dusty ISM.
opacity dust in clumpy gas clouds
the optical depth for all intervening clouds
along the light ray
optical depth of a gas cloud
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Angular momentum transfer in an Inhomogeneous ISM
Total angular momentum loss rate
( NcNumber of clouds)
Mass Accretion Rate
Angular Momentum Extraction
Total mass of the ISM
Estimate for BH mass
( t0Hubble time J total angular momentum )
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Result.1 BH mass-to-morphology relation
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Why MBH are small in disk galaxies?
? ?
?
radiation
pole on view
? A number of photons escaped from the system
(Surface-to-volume ratio )
? Radiation from disk stars is heavily diminished
across the disk (optically thick disk)
? The velocity difference stars and absorbing
clouds becomes closer to zero (optically thick
disk)
Radiation drag cannot work effectively in disk
galaxies !
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Result.2-1 Comparison with the observations
These objects have relatively small BHs compared
with the predictions.
This trend is broadly consistent with theoretical
prediction.
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Result.2-2 Comparison with the observations
Observational data roughly agree with the
prediction .
Sy1 with SB NLSy1 fall appreciably below 0.001
again.
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Summary
1.BH-to-galaxy mass ratio decreases with a
smaller bulge-to-disk ratio, and is reduced
maximally by two orders of magnitude, resulting
in .
The present model also predict BH-to-galaxy mass
ratio depends on the disk scale-height (h),
ltPhysical Reasonsgt
Almost all photons can escape from a disk-like
system, owing to the effect of geometrical
dilution.
The radiation from stars in disk galaxies is
considerably reduced in the optically-thick disk.
The velocity difference stars and absorbing
clouds becomes closer to zero
2.In disk galaxies, the BH-to-bulge mass ratio is
about 0.001 .
It turns out that the formation of SMBH is not
basically determined by disk components, but
bulge components, consistently observational data.
The BH-to-bulge mass ratio is fundamentally
determined by physical constante0.007,
regardless of morphology of host galaxies.
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Grazie mille!
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