qingjuan yu uc berkeley april 21, 2006
DESCRIPTION
Evolution of Accretion Disks around Massive Black Holes: Constraints from the Demography of Active Galactic Nuclei. Qingjuan Yu UC Berkeley April 21, 2006. (2005, ApJ, 634, 901, Qingjuan Yu, Youjun Lu, & Guinevere Kauffmann). (Tremaine et al. 2002). NGC 4258. Galactic center. - PowerPoint PPT PresentationTRANSCRIPT
Evolution of Accretion Disks around Massive Black Holes: Constraints from
the Demography of Active Galactic Nuclei
Qingjuan YuUC Berkeley
April 21, 2006
(2005, ApJ, 634, 901, Qingjuan Yu, Youjun Lu, & Guinevere Kauffmann)
Introduction • QSOs are powered by gas accretion onto MBHs.• Most nearby galaxies host MBHs at their centers.
• Mass growth of MBHs comes mainly from gas accretion due to QSO/AGN phases.
(Lynden-Bell 1969; Rees 1984; Soltan 1982; Small & Blandford 1992; Kormendy & Richstone 1995; Magorrian et al. 1998; Yu & Tremaine 2002 etc.)
Quasar PKS 2349 (HST)
M87 (HST)Quasar PKS 2349 (HST) M87 (HST)
Galactic center
NGC 4258
(Tremaine et al. 2002)
• How does the accretion/luminosity evolve?
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
()
&M ( ) =(1−ε)L ( )
εc2
M ( ) =M i + &M ( ')0
∫ d '
Evolution after the nuclear activityof a QSO/AGN is triggered
• Cosmological evolution of comoving number density of the QSO population:
• Evolution of the characteristic luminosity of the QSO population:
Not meaning
Extracting evolution of accretion from observations
• A single AGN may only represent one specific period in a prolonged phase of nuclear activity.
• A large sample of AGNs with different ages will span all phases of this activity and allow us to extract information about evolution.
• In addition to age, other physical parameters may be important in determining how AGNs evolve, and a statistical method may help to clarify these.
2dF
SDSS
Statistical methods involving a largesample of QSOs/AGNs are required.
Extracting ()
• Local BHs with present-day mass M0:– Triggering history: seed BHs triggered at cosmic time ti;
– Luminosity evolution (M0,) as a function of =t-ti;
tO
QSOLF
ψ (L,t)dt
0
t0∫ = nM (M0 ,t0 ) life(M0 )P(L |M0 )dM00
∞
∫QSOLF local BHMF lifetime probability
(Yu & Lu 2004)
(ignoring BH mergers)
• (M0,) is isolated by connecting QSOLF with local BHs:
(M0,)
life
LL+dL
ψ (L,t)dt
0
t0∫ = nM (M0 ,t0 ) life(M0 )P(L |M0 )dM00
∞
∫QSOLF local BHMF lifetime probability
Luminosity evolution of individual triggered nuclei
seed BHtriggered
(M0,)
LL+dL
ψ (L,t)dt
0
t0∫ = nM (M0 ,t0 ) life(M0 )P(L |M0 )dM00
∞
∫QSOLF local BHMF lifetime probability
P(L | M0) or
life(M0 )P(L |M0 )
seed BHtriggered
Accretion rate distribution of SDSS nearby AGNs
(Yu, Lu & Kauffmann 2005)
Accretion rate distribution of SDSS nearby AGNs
Normalized mass accretion rate:
&m[OIII] ≡ fL[OIII]
LEdd(M f )
f : average bolometric correction
between L[OIII] and Lbol;
M f (σ ) : average final mass.
SDSS sample: (Kauffmann et al. 2003; Heckman et al. 2004)
z < 0.3;binning &m[OIII] and σ;
σ : 70 → 200km/ s; M f (σ ) : 2.0 ×106 → 1.3×108 Msun.
Accretion rate distribution of SDSS nearby AGNs
Accretion rate evolution &M bol ( ) P( &Mbol |M f )dlog10
&Mbol
≡( &Mbol ln10)dlog10
&Mbol
d &M bol ( ) d =k
k∑
k: solutions of &M bol ( ) = &Mbol
(k=1,2,...).
-Assumed accretion rate evolution:
&M ∝
expτ
τ Sp
⎛
⎝⎜
⎞
⎠⎟, 0 < τ < τ I ;
τ − τ I + τ D
τ D
⎛
⎝⎜⎞
⎠⎟
−γ
, τ ≥ τ I .
⎧
⎨
⎪⎪
⎩
⎪⎪
III
I
Accretion rate distribution of SDSS nearby AGNs
-Assumed accretion rate evolution:
&M bol ∝
expSp
⎛
⎝⎜
⎞
⎠⎟, 0 < < I ;
− I +D
D
⎛
⎝⎜⎞
⎠⎟
−γ
, ≥ I .
⎧
⎨
⎪⎪
⎩
⎪⎪
III
I
γ =1.3 ± 0.1,
τ D = 3.1 ± 1τ Sp .
(Yu, Lu & Kauffmann 2005)
Evolution model of accretion disks:
• Evolution of surface mass density:
• Self-similar solutions (Pringle 1974):
Σ(R,τ )
Σ0
=τ
τ 0
⎛
⎝⎜⎞
⎠⎟
η
fR
R0
⎛
⎝⎜⎞
⎠⎟τ
τ 0
⎛
⎝⎜⎞
⎠⎟
ξ⎡
⎣⎢⎢
⎤
⎦⎥⎥
∂Σ∂
=3
R
∂
∂RR1/2 ∂
∂R(νΣR1/2 )⎡
⎣⎢⎤⎦⎥, ν ∝ ΣmRn;
&M disk ∝−38+18a+4b32+17a+2b ∝
−1.18 , (a=b=0;Thomson opacity); −1.25 , (a=1,b=7 / 2;Kramers opac.)
⎧⎨⎩
opacity :κ (ρ,T ) ∝ ρaT−b
(Cannizzo, Lee, & Goodman 1990)
Evolution model of accretion disks:
• Diffusion timescale
• Consistency of observations with simple theoretical expectations suggests that the accretion process in nearby AGNs follows a self-similar evolutionary pattern.
0 =R0
2
ν (R0 , Σ0 )= (0.1 − 1.6) × 108 yr
R0
0.3 − 1pc
⎛⎝⎜
⎞⎠⎟
7 /3M BH
107 M sun
⎛
⎝⎜⎞
⎠⎟
1/3α
0.1⎛⎝⎜
⎞⎠⎟
−4 /3 M d ,0
107 M sun
⎛
⎝⎜⎞
⎠⎟
−2/3
T Tauri star
• Disk accretion: self-similar evolution
&M disk ∝ −η
(Hartmann et al. 1998)
Diversity of Eddington ratios (Lbol/Ledd) in QSOs/AGNs
(Mclure & Dunlop 2004)
(Woo & Urry 2002)
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The diversity in the Eddington ratios is a natural result of the long-term evolutionof accretion disks in AGNs.
Discussions
• Further issues related to long-term evolution of accretion disks:– Disk winds, infalling material deposited onto the disk, instabilities, self-gravitating disks, star formation …
• Binary black holes and coevolution of galaxies and QSOs/AGNs
Discussions
• Adding the effect of an evolving accretion disk in unified models of AGNs– Lack of a torus in very weak AGNs
– Radiatively inefficient accretion
Summary • The accretion rates in most nearby Seyfert galaxies (with host galaxy velocity dispersion sigma~70-200km/s, z<0.3) are declining with time in a power-law form and the accretion process follows a self-similar evolutionary pattern as simple theoretical models predict.
• Some other issues deserves of further investigation, such as the long-term evolution of accretion disks, the evolution of BBHs in QSOs/AGNs, coevolution of galaxies and QSOs/AGNs, and the unification picture of AGNs.
Alternative explanation for the accretion rate
distribution• Fueling low-level AGN activity through the stochastic accretion of cold gas, astro-ph/0603180, Hopkins & Hernquist– Feed-back driven model in a large-scale context
But how can the evolution of accretion disks be avoidable?