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AY202a Galaxies & Dynamics Lecture 14: Galaxy Centers & Active Galactic Nuclei.

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Presentation on theme: "AY202a Galaxies & Dynamics Lecture 14: Galaxy Centers & Active Galactic Nuclei."— Presentation transcript:

1 AY202a Galaxies & Dynamics Lecture 14: Galaxy Centers & Active Galactic Nuclei

2 Galaxy Centers History AGN Discovered way back when --- Fath 1908 Broad lines in NGC1068 Seyfert 1943 Strong central SB correlates with broad lines Growing evidence over the years that there was a central engine and that the central engine must be a black hole! And, what about galaxies that are not AGN?

3 Masers in NGC4258 microarcsec proper motions with VLBI

4 Reverberation Mapping Blandford & McKee ’82,  Peterson et al. Assume 1. Continuum comes from a single central source 2. Light travel time is the most important timescale τ = r/c 3. There  a simple (not necessarily linear) relation between the observed continuum and the ionizing continuum.

5  L(V,t) = ∫  (V,τ)  C(t-τ) dτ Velocity delay map Continuum light curve relative to mean


7 Lag relative to 1350A = 12 Lyα, 26 CIII], 50 MgII N5548

8 Kaspi et al R vs L & M vs L From Reverberation Mapping

9 Greene & Ho SDSS AGN M ● vs σ

10 Greene & Ho Push to low M Log (M ● /M  ) = (σ/200 km/s)

11 Barth, Greene & Ho

12 BH Mass Function Greene & Ho ‘07

13 Active Galactic Nuclei 1943 Carl Seyfert Sy1 = Broad Balmer lines 10 4 km/s Sy2 = Intermediate width lines ’s Jansky, Ryle detected Radio Sources 1960’s Radio Galaxies ID’d Baade & Minkowski Virgo A = M87, Cygnus A, NGC5128, NGC Greenstein & Schmidt identified QSO’s (3C48 z=0.367, 3C273 z =0.158)

14 General Properties Compact central source  energy density high, dominates host galaxy Non-thermal spectrum Optical/UV - general shows strong emission lines from dense and less dense regions. Polarization (1-10%), jets Radio – jets, lobes, compact sources X-rays --- Power law spectrum, often into the Mev Gamma rays --- detection of some sources like BL Lac’s into the TeV Variability

15 Classifications Sy1/QSO = Type I Broad permitted lines km/s narrower forbidden lines 10 3 km/s, BLRG QSR = radio loud, QQ = radio quiet Sy2 = Type II narrower lines, all ~ 10 3 km/s line ratios indicative of photoionization by a non-thermal (power law) spectrum, NLRG BL Lac = Blazar continuum emission only, usually strong radio and/or x-ray source, polarized LINER = Low ionization nuclear emission line region OVV = Optically Violent Variable  QSO, Blazar

16 HαHα HH NGC5940 Sy1 [OIII] ns

17 NGC4151 Sy1.2

18 [OI] [OI] [SII] HαHα [NII]

19 NGC4388 Sy2

20 NGC3998 LINER

21 High S/N Optical Peterson

22 High S/N UV

23 LBQS Mean QSO Spectrum

24 Common Emission Lines in AGN

25 Spectral Classification by Line Ratio Baldwin, Terlevich & Phillips (based on Osterbrock) Star Forming LINER Seyferts/QSOs

26 Electron Density from Line Ratios Intensity ratio changes as collisional depopulation begins to dominate [SII] doublet 6717 &6731A radiative collisional Peterson, Pogge based on Osterbrock radiative collisional

27 Temperature from Line Ratios Relative population of states depends on temperature [OIII] 4363 and the doublet Peterson, Pogge based on Osterbrock

28 Real or Memorex? Classification can depend on how you look --- total vs polarized. (Miller et al.) looks a lot like a Sy1!

29 Fanaroff-Riley Classification Fanaroff & Riley (1974) noted that radio source structure was correlated source luminosity FR I – weak sources, bright centers decreasing surface brightness to the edge FR II – have limb brightened regions of enhanced emission 1400 Mhz vs MB from Owen & Ledlow ‘94

30 FR I (3C449, Perley et al ’79) FR II (3C47, Bridle et al. ’94)

31 David W. Hogg, Michael R. Blanton, and the Sloan Digital Sky Survey Collaboration


33 Cen A Chandra

34 3C273

35 Optical Radio X-ray Comp


37 Superluminal Motions 3C279 (NRAO) Keel VLBI

38 Consider two blobs, one stationary and one moving away from it at a velocity c  at an angle of  to the line-of-sight. Apparent transverse velocity is v = which has a maximum at v ~  c  = 1/(1-  2 ) 1/2  c sin(  ) 1-  cos(  )

39 Spectral Energy Distributions

40 Basic Models 1959 Woltjer’s argument --- (1) centers of AGN very small, r 1000 km/s, so by GM/r ~ v2  M > (r/100pc) M  So either M is really big, implying a very high mass density inside r, or r is much smaller, implying a very high energy density at the center - or both.

41 Continuum Spectrum best described as Synchrotron-Self Compton + thermal emission from an accretion disk + dust & stars, + lines from the gas. SSC  Synchrotron spectrum with a low frequency turnover due to self absorption and a high frequency break due to Compton losses and an x- ray-HE spectrum from inverse Compton scattering from the relativistic electrons

42 Synchrotron Spectrum Depends on the energy spectrum of the electrons, e.g. for n(E) = N E –S /4  = W(E/mc 2 ) –S /4  where E/mc 2 is usually abbreviated as γ the power, P, emitted per unit volume is dP/dV = 1.7x10 21 N a(S) B(4.3x10 6 B/ ) (S-1)/2 (volume emissivity) ergs/s/cm3/Hz B = magnetic field in Gauss, a(s) ~0.1 for 1.5

43 Synchrotron m  B 1/5 F 2/5  -4/5

44 SSC Model fit to Mk501 spectrum (Konopelko 2003) Synchrotron Peak Self-Compton

45 SED High and Low γ-ray states M. Boettcher


47 Accretion Disks To first order, assume it radiates as a black body F( ) = where T(r) is the disk temperature at radius r 2h 2 1 c 2 e h /kT(r) -1

48 Multi-component Models Malkan 1983

49 References B. Peterson, An Introduction to Active Galactic Nuclei (Cambridge 1997) J. Krolik, Active Galactic Nuclei (Princeton 1999)

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