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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galaxy centers
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?

slide3
Masers in NGC4258

microarcsec proper motions with VLBI

reverberation mapping
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.

slide7

N5548

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

slide8
Kaspi et al R vs L

& M vs L

From Reverberation Mapping

slide10
Greene

& Ho

Push to low M

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

slide11
Barth,

Greene

& Ho

slide12
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)

slide14
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

classifications
Classifications

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

slide16

NGC5940 Sy1

[OIII]

H

ns

slide18

NGC4151 Sy1.2

[NII]

[NII]

[OI] [OI]

[SII]

spectral classification by line ratio
Spectral Classification by Line Ratio

Seyferts/QSOs

Baldwin,

Terlevich

& Phillips

(based on

Osterbrock)

Star Forming

LINER

slide26
Electron Density from Line Ratios

Intensity ratio changes as

collisional depopulation

begins to dominate

radiative

radiative

collisional

[SII] doublet

6717 &6731A

collisional

Peterson, Pogge based on Osterbrock

slide27

Temperature from Line Ratios

Relative population of states depends on temperature

[OIII] 4363 and the 4959+5007 doublet

Peterson, Pogge based on Osterbrock

slide28
Real or Memorex?

Classification can

depend on how you

look --- total vs

polarized.

(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

edge

FR II – have limb brightened

regions of enhanced emission

1400 Mhz vs MB from

Owen & Ledlow ‘94

slide30

FR I

(3C449,

Perley et al ’79)

FR II

(3C47,

Bridle et al. ’94)

slide33
Cen A

Chandra

slide35
Optical

Radio

X-ray

Comp

superluminal motions
Superluminal Motions

3C279 (NRAO)

VLBI

Keel

slide38
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()

basic models
Basic Models

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.

slide41
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

synchrotron spectrum
Synchrotron Spectrum

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

slide43
Synchrotron Peak

@ m  B1/5 F2/5 -4/5

slide44

Synchrotron Peak

SSC Model

fit to Mk501

spectrum

(Konopelko 2003)

Self-Compton

slide45
SED

High and

Low γ-ray

states

M. Boettcher

accretion disks
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

c2 eh/kT(r) -1

references
References

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

J. Krolik, Active Galactic Nuclei (Princeton 1999)

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