Ay202a galaxies dynamics lecture 14 galaxy centers active galactic nuclei
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AY202a Galaxies & Dynamics Lecture 14: Galaxy Centers & Active Galactic Nuclei. Galaxy Centers. History AGN Discovered way back when --- Fath 1908 Broad lines in NGC1068 Seyfert 1943 Strong central SB correlates with broad lines

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Ay202a galaxies dynamics lecture 14 galaxy centers active galactic nuclei

AY202a Galaxies & DynamicsLecture 14:Galaxy Centers &Active Galactic Nuclei

Galaxy centers
Galaxy Centers


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?

Masers in NGC4258

microarcsec proper motions with VLBI

Reverberation mapping
Reverberation Mapping

Blandford & McKee ’82,  Peterson et al.


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.

L v t v c t d

Continuum light curve relative to mean

L(V,t) = ∫ (V,τ) C(t-τ) dτ

Velocity delay map


Lag relative to 1350A = 12 days @ Lyα, 26 days @ CIII], 50 days @ MgII

Kaspi et al R vs L

& M vs L

From Reverberation Mapping


& Ho

Push to low M

Log (M●/M) = 7.96 + 4.02 (σ/200 km/s)



& Ho

BH Mass Function

Greene & Ho ‘07

Active galactic nuclei
Active Galactic Nuclei

1943 Carl Seyfert Sy1 = Broad Balmer lines 104 km/s

Sy2 = Intermediate width lines 103

1950’s Jansky, Ryle detected Radio Sources

1960’s Radio Galaxies ID’d Baade & Minkowski

Virgo A = M87, Cygnus A, NGC5128, NGC1275

1963 Greenstein & Schmidt identified QSO’s

(3C48 z=0.367, 3C273 z =0.158)

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



Sy1/QSO = Type I Broad permitted lines 104+ km/s

narrower forbidden lines 103 km/s, BLRG

QSR = radio loud, QQ = radio quiet

Sy2 = Type II narrower lines, all ~ 103 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


NGC5940 Sy1





NGC4151 Sy1.2



[OI] [OI]


Spectral classification by line ratio
Spectral Classification by Line Ratio




& Phillips

(based on


Star Forming


Electron Density from Line Ratios

Intensity ratio changes as

collisional depopulation

begins to dominate




[SII] doublet

6717 &6731A


Peterson, Pogge based on Osterbrock

Temperature from Line Ratios

Relative population of states depends on temperature

[OIII] 4363 and the 4959+5007 doublet

Peterson, Pogge based on Osterbrock

Real or Memorex?

Classification can

depend on how you

look --- total vs


(Miller et al.)

looks a lot like a Sy1!

Fanaroff riley classification
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


FR II – have limb brightened

regions of enhanced emission

1400 Mhz vs MB from

Owen & Ledlow ‘94



Perley et al ’79)



Bridle et al. ’94)

Cen A Sky Survey Collaboration


3C273 Sky Survey Collaboration

Optical Sky Survey Collaboration




Superluminal motions
Superluminal Motions Sky Survey Collaboration

3C279 (NRAO)



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()

Spectral energy distributions
Spectral Energy Distributions it at a velocity c

Basic models
Basic Models it at a velocity c

1959 Woltjer’s argument --- (1) centers of AGN very small, r < 100 pc, (2) typical line widths are v > 1000 km/s, so by

GM/r ~ v2  M > 1010 (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.

Continuum Spectrum it at a velocity cbest 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

Synchrotron spectrum
Synchrotron Spectrum it at a velocity c

Depends on the energy spectrum of the electrons, e.g. for

n(E) = N E–S /4 = W(E/mc2)–S /4

where E/mc2 is usually abbreviated as γ

the power, P, emitted per unit volume is

dP/dV = 1.7x1021 N a(S) B(4.3x106 B/)(S-1)/2

(volume emissivity) ergs/s/cm3/Hz

B = magnetic field in Gauss, a(s) ~0.1 for 1.5<S<5

power law spectrum slope is related to energy spectrum slope ~ (S-1)/2

See Ginzburg & Syrovatskii 1964, Sov AJ 9, 683

1965, AR 3, 297, 1969 AR 7, 375

Blumenthal & Gould 1970 Rev Mod Phys 42, 237

Synchrotron Peak it at a velocity c

@ m  B1/5 F2/5 -4/5

Synchrotron Peak it at a velocity c

SSC Model

fit to Mk501


(Konopelko 2003)


SED it at a velocity c

High and

Low γ-ray


M. Boettcher

Accretion disks
Accretion Disks it at a velocity c

To first order, assume it radiates as a black body

F() =

where T(r) is the disk temperature at radius r

2h2 1

c2 eh/kT(r) -1

Multi component models
Multi-component Models it at a velocity c

Malkan 1983

References it at a velocity c

B. Peterson, An Introduction to Active Galactic Nuclei (Cambridge 1997)

J. Krolik, Active Galactic Nuclei (Princeton 1999)