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活动星系核统一模型和 超大质量黑洞的形成与增长. 张双南 清华大学物理系和天体物理中心 科学院高能所粒子天体物理重点实验室. Emission Line Spectra from Seyfert AGNs. Broad emission lines from Type-I Seyfert AGN. Narrow emission lines from Type-II Seyfert AGN. Unification scheme for type-I and type-II AGNs.
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活动星系核统一模型和超大质量黑洞的形成与增长活动星系核统一模型和超大质量黑洞的形成与增长 张双南 清华大学物理系和天体物理中心 科学院高能所粒子天体物理重点实验室
Emission Line Spectra from Seyfert AGNs Broad emission lines from Type-I Seyfert AGN Narrow emission lines from Type-II Seyfert AGN
Investigation of the obscuring circumnuclear torus in the active galaxy Mrk231: Kloeckner et al., Nature, 2003 The inferred model of the nuclear torus. The molecular material moves from top right to bottom left (northwest to southeast). Virial estimates of the central mass concentration give (7.2±3.8) x107 solar masses.
Sky deep surveys of Chandra and HST show that the fraction of type II AGN is decreasing with the hard X-ray luminosity. • Hasinger et al 2003 • Similar correlation has been found by Steffen et al. (2003). Sazonov & Revnivtsev (2004), Wang & Zhang (2004) in other samples of AGNs This indicates a breakdown of the ‘strong’ unification model where the covering factor H/Ri is independent of luminosity and redshift. This has been taken as the evidence of evolution of torus geometry
Anisotropy of X-ray emission from AGNs In all previous studies, it has been assumed implicitly that However, if the X-rays originate from the accretion disk surrounding the black hole, the observed apparent X-ray luminosity is related to its intrinsic luminosity by: Then for a given X-ray luminosity, randomly oriented AGNs will have apparent luminosity distribution:
The inclination angle effect Data from Ueda et al. 2003 Zhang, 2005, ApJ, 618, L79
The inclination angle effect on type-II AGN fraction Zhang, 2005, ApJ, 618, L79
考虑相对论效应对光度的修正 Better agreement than non-relativistic model
考虑相对论效应对能谱的修正 Sy 2 spectra are harder than Sy 1 spectra for Kerr BHs a=0.998 倾角: 5 40 85 α : 0.89 0.85 0.75 (0.01)
Anisotropy of inverse Compton scattering in corona Maraschi & Haardt 1997 θ=0o θ=60o Higher inclination for Softer spectrum! Disk kT=50 eV Disk kT=100 eV
Inclination angle dependence of 2-10 keV spectral index Zdziarski et al. 2000 Anisotropy of inverse Compton scattering in spherical corona Averaged Sy I index Malizia et al. 2003 Relativistic effects (Disk origin in 2-10 keV) Sy II index
Implications of this TAXI model • TAXI model: Torus of Antonucci with X-ray Inclination-angle effects • X-rays are produced primarily in accretion disk, but not in extended and near-spherical corona • Many similarities in X-ray variabilities between X-ray binaries and AGNs suggest disk origin • Several theoretical models suggest viable mechanisms for X-ray production from AGN disks, e.g., magnetic reconnection (like in the Sun), magnetic turbulent Comptonization • Lack of broad Fe-K-alpha emission lines • Accretion disk and the torus are co-aligned with each other • Consistent with the model of Krolik and Begelman (1988) in which the torus feeds the black hole. • Question to be answered: How does the torus form the accretion disk surrounding the black hole?
Important correlations of SMBH mass with properties of galactic bulge Black holes grow together with their host bulges. Ionized gas dynamics Stellar dynamics Maser disk dynamics
No SMBH in M33? Merritt, et al, 2001, Science • The M33 galaxy • 850 kpc • spiral (disk) galaxy • with nuclear star cluster • expected to host a BH • But no bulge • No sharp increase of either V or towards the center of the galaxy • Mass of the BH: < 3103M⊙ BH grow together only with their host bulges, not with their disks.
Positive slope: stable disk Negative slope: unstable disk Unstable by design:Siemiginowska and Elvis, Nature, 1999 • Lower stable branch: viscous heating balanced by cooling (BB radiation) • Higher stable branch: viscous heating balanced by cooling (thermal Bremsstralung radiation) • Middle unstable branch: UV photons strongly absorbed by hydrogen (ionization), cooling inefficient. • Increate accretion rate • Increase UV absorption • Jumps between lower and higher branches
Advantages of the instability model • Previous problem for quasars • High luminosity high accretion rate • Fuel run out quickly many dead quasars in nearby galaxies: not found • New understanding • High luminosity implies the quasar disks cannot be in the lower branch • Irradiation of the disk insufficient to keep it in the higher branch permanently • Active quasars are those in the higher branch temporarily, due to irradiation instability
An Accretion Model for the Growth of the Central BH Associated with Ionization Instability in Quasars: Lu, Cheng, Zhang, ApJ, 2003 • AGNs produce strong radiation because the BH accretes material from the host galaxy: • A BH may acquire significant mass through accretion • The accretion disk may not deliver all its material to the BH, as inferred from outflows in the forms of jets and galactic winds: • The ejected material may form the bulge • So we proposed an accretion model for the coeval growth of BH and bulge.
Model Assumptions • Assume an initial seed BH and disk are present. • Assume accretion rate of the disk in the higher branch of the S-shape is near Eddington-limit, and is thus modeled by the optically thick and geometrically thin solution. • Assume a sufficient cold gas is supplied by the quasar host galaxy. • Assume the disk in the lower branch of S-shape is modeled by relativistic advection dominated inflow-outflow solution (ADIOS).
Basic equations Higher branch: Keplerian model (Pringle 1981; Smak 1984) Lower branch: ADIOS model (Becker et al.2001) 0.025<<0.1
Radiation efficiency in the lower branch: 0.025<<0.1 The accreted matter (Mbh)acc is about 10-3 of the total outflowing mass Mout. Based on model parameters for the accretion rates in different branches: a seed BH with mass 2106M⊙, can grow up to BH with mass 2108 M⊙ within 10 Gyr.
The massive seed BH problem in the early Universe • One common problem for any kind of BH growth model: how was the massive seed BH (> 106M⊙) produced in the early Universe? • Some extremely massive BHs (>109M⊙) are found at very high redshift.
SMBH formation in the early Universe:Shen, Hu, Lou & Zhang, submitted to ApJ • First generation stars ~100 M⊙ (made of primordial material, almost entirely H and He) formed at z~30, but evolved quickly into supernova and left 10-100 M⊙ BHs • A two-phase accretion model of SMBH formation: • a rapid accretion mainly of self-interacting dark matter (SIDM) onto 10-100 M⊙ BHs to form MBH~106M⊙ at very high redshift (z ~ 15 - 20) • a subsequent growth via normal baryonic accretion at the Eddington limit to MBH ~109M⊙ before redshift z ~ 6.
Self-Interacting Dark Matter (SIDM) Accretion • Simulations of structure formation in the Universe prefer SIDM model (angular momentum) with specific cross section: ~ • The first large-scale structures formed are dark matter halo. Assuming isothermal density profile • Then the BH mass growth:
Baryonic Eddington Accretion Phase • Exponential growth of BH mass via baryonic Eddington accretion: Salpeter (1964) • To make 109M⊙ from 106M⊙, it takes 5×108 years, i.e., just a few percent of the age of the Universe • However such SMBHs in the early Universe are very rare → most quasars are not accreting at Eddington rate continuously←our S-curve instability BH growth model • Persistent BH binaries are also very rare; most BH binaries are transients (the same S-curve). Coincident?
Summary • Unification model of Active Galactic Nuclei • BH + Accretion Disk + Dusty Torus; Disk and Torus are coplanar • Most EM-radiation from disk and the torus covers part of the disk • Observed disk flux is inclination angle dependent: Type I AGNs are normally brighter than Type II AGNs • Two models coeval growth of supermassive BH with bulge • Mergers of smaller systems • Accretion of material from the disk (BH growth) and outflows from the disk (bulge growth) • Formation of seed supermassive BHs • Bondi (spherical) accretion of self-interacting dark matter halo • Growth of some supermassive BHs (in a small percentage of quasars) in the early Universe • Eddington accretion of baryonic matter onto seed supermassive BHs.
Further work and open questions • Is X-ray emission from AGNs really from accretion disk? • Previously the X-ray emission is usually believed from optically thin corona. • If the X-ray emission is really from the disk, then relativistic effects on its continuum spectra should be revealed. • Maybe for individual AGN we can find a way to estimate its inclination angle accurately and then study the spectral correlation with the inclination angle? • For our two phase BH growth model, one important question to ask is: can this model reproduce the observed luminosity function of AGNs? • Which kind of accretion history is required to produce the LF? • How much dark matter is turned into 106 M⊙ in the early Universe? Is there any way to detect these BHs?