Why are Massive Black Holes Small in Disk Galaxies

1
Why are Massive Black Holes Small in Disk
Galaxies ?
Nozomu KAWAKATU Center for Computational Physics,
University of Tsukuba
Collaborator
Masayuki UMEMURA (University of Tsukuba)
Formation of the First Generation of Galaxies
Strategy for the Observational Corroboration of
Physical Scenarios, 3-4 September 2003, Niigata
University, Niigata, Japan
2
INTRODUCTION
Recent high resolution observations of galactic
centers
Supermassive BHs have been thought to be the
central engine of AGNs.

linear relation
(Kormendy Richstone 1995 Richstone et al.
1998 Magorrian et al. 1998 Gebhardt et al.
2000 Ferrarese Merritt 2000 Merritt
Ferrarese 2001 McLure Dunlop 2002)
MBH M
BH mass doesnt correlate with the disk
components.
(Kormendy Gebhardt 2001)
Formation of SMBHs
Physical relation!
Formation of Bulges
Lbulge L
Richstone et al.1998
3
The MBH in disk galaxies are smaller than that in
elliptical galaxies !

Galactic Bulge
10
(Salucci et al. 2000 Sarzi et al. 2001
Ferrarese 2002 Baes et al. 2003)
MBHs do form in some pure disks
8
log MBH
e.g., NGC 4395
6
(using MBH -s relation)
Disk galaxies
4
(Filipenko Ho 2003)
12
13
11
10
log Mgalaxy
Salucci et al. 2000
It has not been clarified physically
why the BH mass is smaller in disk !!
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Theoretical Model for SMBH formation
The physics on the angular momentum transfer is
requisite !
Radiation drag (Poynting-Robertson effect)
A potential mechanism to extract angular momentum
in a spheroidal system
Radiation drag efficiency is determined by the
total number of photons
lt Previous Works gt
The BH-to-bulge mass ratio is determined by the
energy conversion efficiency of nuclear fusion
from hydrogen to helium, i.e., 0.007.
(Umemura 2001)
The inhomogeneity of ISM helps the radiation
drag to sustain the maximal efficiency.
(Kawakatu Umemura 2002 )
ISM is observed to highly inhomogeneous in active
star-forming galaxies !
The radiation drag model can account for the
mass ratio observed quantitatively, taking
account of the realistic chemical evolution.
(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, quantitative details are not clear !
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This Work
We built up a simple model of the bulge-disk
system and accurately solve the 3D radiation
transfer in the bulge-disk system in an
optically-thick and inhomogeneous ISM.
To elucidate the relation between the morphology
of host galaxies and the angular momentum
transfer efficiency due to the radiation drag
We disclose the physical reasons
why BHs are smaller in disk
galaxies!
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Model
The difference of morphology is expressed by
changing the bulge fraction (fbulge).
Spatial distribution
Rotational velocity
DM NFW profile
rigid rotation
Stars ISM Bulge Hernquists profile Disk
exponential profile
rotation valance
Star Formation History
Salpeter-type initial mass function
SFR is proportional to the fractional gas mass.
Mass-to-Size relation
( bulgetSF108yr, disk tSF109yr)
Optically thick inhomogeneous ISM
Size of gas clouds 100pc
Optical depth of a gas cloud1, 10, 100
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Clumpy ISM Model
Treatment of the radiation tranfser
We calculate the radiation fields by the direct
integration of the radiation transfer.
Opacity dust in clumpy gas clouds
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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 are
determined.
Mass Accretion Rate
Angular Momentum Extraction
Total mass of the ISM
Estimate for MDO mass
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Result.1 Morphology-to-radiation drag efficiency

Hubble Type
Sd,Sm
Sc
Sb
Sa
S0
E
10-3
Almost constant
mass ratio
10-4
Radiation drag efficiency is reduced
as fbulge is smaller (factor 20) .
Pure disk
0.1
1
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Why the small in disk galaxies?
Radiation drag efficiency the total number of
photons emitted from stars and absorbed by clouds
during the whole history of the galaxy
large
small
The number of photons escaped from the system
Disk components dominant
large
small
Effect of absorption in the optically-thick disk
The distribution of the ISM is closer to uniform
Difference between the velocity of a star and a
ISM is closer to zero.
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Result.2-1 Comparison with the observations
Hubble Type
Sd,Sm
Sc
Sb
Sa
S0
E

Normal spiral and barred galaxies
Sy1 (Errors of BH fractionfactor 3)
NGC3245
NLSy1
?
Sy2
NGC4151
our prediction ( upper limit is AGN activity)
NGC5548
M81
10-3
M31
NGC3783
NGC1023
MBH / Mgalaxy
Mrk509
Fairall 9
NGC4258
NGC3516
IC4329A
NGC4593
10-4
3C120
Galaxy
(NLSy1)
NGC7469
(Starburst-Sy1)
Mrk590
NGC4945
(NLSy1)
NGC4051
NGC1068
NGC7457
(NLSy1)
1
0.1
NGC4395 (pure disk)
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Result.2-2 Comparison with the observations
Hubble Type
Sd,Sm
Sc
Sb
S0
E
Sa
NGC4258
M31
NGC3245
NGC4151
NGC7457
IC4329A
Fairall 9
NGC3783
NGC5548
NGC1023
Mrk509
NGC4945
10-3
M81
MBH / Mbulge
NGC1068
3C120
NGC3516
Galaxy
(NLSy1)
NGC4593
our prediction ( upper limit is AGN activity)
10-4
NGC7469
Mrk590
NGC4051
(Starburst-Sy1)
(NLSy1)
(NLSy1)

Normal spiral and barred galaxies
Sy1
Sy2
NLSy1
?
0.1
1
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Result.3 Ellipticity-to-radiation drag efficiency
Morphology Type
E7
E6
E5
E4
E3
E2
E1
E0
10-2
Observational Data (Marconi Hunt 2003)
Drag efficiency decrease as the axis ratio is
smaller (factor 3).
b
a
MBH / Mbulge
10-3
our prediction ( upper limit is AGN activity)
10-4
0.3
0.5
0.6
0.7
0.8
0.9
1.0
0.4
Axis ratio (b/a)
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Conclusions
By assuming a simple model of a galactic bulge
and disk, we have investigated the relation
between the morphology of host galaxies and the
radiation drag efficiency. In a clumpy ISM and an
aspherical system, we have accurately solved 3D
radiation transfer to calculate the radiation
drag force by the rotating stars.
1.The radiation drag efficiency is sensitively
dependent on the morphology of host galaxies. The
disk galaxies have almost twenty times as small
BHs as elliptical ones.
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.
2.If only the bulge in a disk galaxy is taken,
the BH-to-bulge mass ratio is about 0.001 .
It turns out that the formation of MBH is not
basically determined by the disk components, but
bulge components.
This is consistent with the recent observational
results!!
3. For the same reason, the mass ratio could be
lower than for a flattened bulge.
Our model predicts the mass ratio correlates with
the ellipticity of the galactic bulge.