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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) 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.) (Tremaine et al. 2002) NGC 4258 Quasar PKS 2349 (HST) Quasar PKS 2349 M87 (HST) (HST) Galactic center M87 (HST) • How does the accretion/luminosity evolve? () Quic kTime™ and a TIFF (Unc ompres sed) dec ompres sor are needed to see this pic ture. Evolution after the nuclear activity of a QSO/AGN is triggered (1 )L( ) M&( ) c2 M ( ) M M&( ')d ' i 0 Not meaning • Evolution of the characteristic luminosity of the QSO population: • Cosmological evolution of comoving number density of the QSO population: Extracting evolution of accretion from observations Statistical methods involving a large sample of QSOs/AGNs are required. 2dF SDSS • 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. 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; • O QSOLF t (M0,) is isolated by connecting QSOLF with local BHs: (ignoring BH mergers) t0 0 (L,t)dt nM ( M 0 ,t0 ) life ( M 0 )P(L | M 0 )dM 0 0 QSOLF local BHMF lifetime probability (Yu & Lu 2004) Luminosity evolution of individual triggered nuclei (M0,) L+dL L seed BH triggered life t0 0 (L,t)dt nM ( M 0 ,t0 ) life ( M 0 )P(L | M 0 )dM 0 0 QSOLF local BHMF lifetime probability P(L | M 0 ) or (M0,) life ( M 0 )P(L | M 0 ) L+dL L seed BH triggered t0 0 (L,t)dt nM ( M 0 ,t0 ) life ( M 0 )P(L | M 0 )dM 0 0 QSOLF local BHMF lifetime probability Accretion rate distribution of SDSS nearby AGNs (Yu, Lu & Kauffmann 2005) Accretion rate distribution of SDSS nearby AGNs Normalized mass accretion rate: m&[OIII] f L[OIII] LEdd (M f ) f : average bolometric correction between L[OIII] and Lbol ; M f ( ) : average final mass. SDSS sample: (Kauffmann et al. 2003; Heckman et al. 2004) z 0.3; binning m[OIII] and ; : 70 200km / s; M f ( ) : 2.0 10 6 1.3 10 8 M sun . Accretion rate distribution of SDSS nearby AGNs Accretion rate evolution M&bol ( ) P( M&bol | M f )d log10 M&bol ( M&bol ln10)d log10 M&bol k dM& ( ) d bol k k : solutions of M&bol ( ) M&bol (k 1, 2,...). -Assumed accretion rate evolution: 0 I; exp , Sp M& I D I. , D I II I Accretion rate distribution of SDSS nearby AGNs -Assumed accretion rate evolution: 0 I; exp , Sp M&bol I D , I. D I I 1.3 0.1, II 3.1 1 . D Sp (Yu, Lu & Kauffmann 2005) Evolution model of accretion disks: • Evolution of surface mass density: 3 1/2 1/2 R ( R ) , R R R m Rn ; • Self-similar solutions (Pringle 1974): (R, ) R f 0 0 R0 0 M&disk 38 18a 4b 32 17a 2b 1.18 , (a b 0; Thomson opacity); 1.25 , (a 1,b 7 / 2;Kramers opac.) opacity : ( ,T ) aT b (Cannizzo, Lee, & Goodman 1990) Evolution model of accretion disks: • Diffusion timescale R02 R0 0 (0.1 1.6) 10 8 yr 0.3 1pc (R0 , 0 ) 7/3 M BH 10 7 M sun 1/ 3 0.1 4 / 3 M d,0 10 7 M sun 2 / 3 • Consistency of observations with simple theoretical expectations suggests that the accretion process in nearby AGNs follows a self-similar evolutionary pattern. T Tauri star M&disk • Disk accretion: self-similar evolution (Hartmann et al. 1998) Diversity of Eddington ratios (Lbol/Ledd) in QSOs/AGNs QuickTime™ and a TIFF (Uncompressed) decompr are needed to see this pictur (Mclure & Dunlop 2004) The diversity in the Eddington ratios is a natural result of the long-term evolution of accretion disks in AGNs. (Woo & Urry 2002) 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?