ｽﾗｲﾄﾞﾀｲﾄﾙなし

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
INTRODUCTION
Recent high resolution observations of galactic centers
¶ Supermassive BHs have been thought to be the central engine of AGNs.
¶ M BH M bulge
0.001  0.006
(Kormendy & Richstone 1995; Richstone et al. 1998;
Magorrian et al. 1998; Gebhardt et al. 2000;
Ferrarese & Merritt 2000; Merritt & Ferrarese 2001;
McLure & Dunlop 2002)
linear relation
M BH M bulge  0.005
¶ BH mass doesn’t correlate with
the disk components.
(Kormendy & Gebhardt 2001)
Formation of SMBHs
Physical relation!
Formation of Bulges
Lbulge [L ]
Richstone et al.1998
The MBH in disk galaxies are smaller than that in elliptical galaxies !
¶
M BH M galaxy  0.001
(Salucci et al. 2000; Sarzi et al. 2001; Ferrarese
2002; Baes et al. 2003)
¶ MBHs do form in some pure disks
10
Galactic Bulge
M BH M bulge  0.001
8
e.g., NGC 4395
M BH
6.6 104 M
(using MBH -σ relation)
 M BH M galaxy 1.3 105
(Filipenko & Ho 2003)
6
Disk galaxies
4
10
11
log Mgalaxy
12
13
Salucci et al. 2000
It has not been clarified physically
why the BH mass is smaller in disk !!
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
Total accreted mass onto “massive dark object” (MDO) in optically thick regime
M MDO


0
Lbulge
c
2
dt
Lbulge :total luminosity of the bulge
“Radiation drag efficiency is determined by the total number of photons”
< Previous Works >
¶ 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 )
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 !
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 opticallythick 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!
Model
rdisk
rbulge
The difference of morphology is
expressed by changing the bulge
fraction (fbulge).
fbulge  M bulge M galaxy
h  0.1rg
• Spatial distribution ( N*  300, Ngas  104 )
DM： NFW profile
Stars & ISM：
M bulge  M disk
Bulge: Hernquist’s profile
Disk: exponential profile
• Mass-to-Size relation
2
M bulge M galaxy   rbulge rg 
M disk M galaxy   rdisk rg 
• Rotational velocity
M bulge  M disk rigid rotation (   0.05)
2
(Mgalaxy  1011 M , rg  10kpc)
rotation valance
• Star Formation History
Salpeter-type initial mass function
SFR is proportional to the fractional gas mass.
( bulge:tSF=108yr, disk: tSF=109yr)
• Optically thick & inhomogeneous ISM
Size of gas clouds : 100pc
Optical depth of a gas cloud:1, 10, 100
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
Basic Equations
The Eq.of Ang.Mom.Transfer
1 d  rv    
 F  (E  P )v
r dt
c
c
Radiation Flux Radiation Drag
  nd d g ： mass extinction due to
dust opacity
E　: radiation energy density
F  : radiation flux
P : radiation stress tensor
The gain and loss of total angular momentum are determined.
Mass Accretion Rate
d ln J
M  M g
dt
Total mass of the ISM
Estimate for MDO mass
t
M MDO   Mdt
0
Angular Momentum
Extraction
Result.1: Morphology-to-radiation drag efficiency
Sd,Sm
Hubble Type
Sc
Sb
Sa
S0
E
M BH M bulge
10-3
Almost constant
MBH Mbulge 8104 1.8 103
M BH M galaxy
10-4
Radiation drag efficiency is reduced
as fbulge is smaller (factor 20) .
Pure disk
0.1
M bulge M galaxy
1
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
small
The number of photons escaped from the system
large
Disk components dominant
small
Effect of absorption in the optically-thick disk
large
The distribution of the ISM is closer to uniform
Difference between the velocity of a star and a ISM is closer to zero.
Result.2-1: Comparison with the observations
Hubble Type
Sc
Sb
Sd,Sm
S0
Sa
E
× Normal spiral and barred galaxies
Sy1 (Errors of BH fraction:factor 3)
Sy2 ▲ NLSy1
10-3
our prediction ( upper limit
is AGN activity)
M31
NGC4258
Fairall 9
NGC3245
NGC4151
NGC5548
M81
NGC3783
NGC
1023 Mrk509
IC4329A
NGC4593
10-4
Galaxy
3C120
(NLSy1)
Mrk590
(NLSy1)
NGC4945
NGC7457
NGC7469
(Starburst-Sy1)
NGC4051
(NLSy1)
NGC1068
NGC4395 (pure disk)
NGC3516
1
0.1
M bulge M galaxy
Result.2-2: Comparison with the observations
Hubble Type
Sc
Sb
Sd,Sm
NGC4258
NGC7457
10-3
IC4329A
M31
Fairall 9
NGC4151
S0
E
NGC3245
NGC3783 NGC5548
NGC1023
Mrk509
NGC4945
M81
NGC1068
Galaxy
10-4
Sa
3C120
(NLSy1)
NGC4593 NGC3516
our prediction ( upper
limit is AGN activity)
NGC4051
(NLSy1)
Mrk590 NGC7469
(NLSy1) (Starburst-Sy1)
× Normal spiral and barred galaxies
Sy1
▲ NLSy1
0.1
Sy2
1
M bulge M galaxy
Result.3 Ellipticity-to-radiation drag efficiency
10-2
E7
E6
Morphology Type
E5
E4
E3
E2
E1
E0
0.9
1.0
Observational Data (Marconi & Hunt 2003)
“Drag efficiency decrease as the
axis ratio is smaller (factor 3).”
b
a
10-3
our prediction ( upper
limit is AGN activity)
10-4
0.3
0.4
0.5
0.6
Axis ratio (b/a)
0.7
0.8
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.
＜Physical Reasons＞
• 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.

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