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Active Galaxies

2Outline

• Normal (boring) galaxies• Active (fun) galaxies• The extragalactic zoo• Components of an active galaxy

– Supermassive Black Holes– Jets– Hot spots and the evolution of radio galaxies

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~20o

VLSS FIELD 1700+690θ~80”, rms ~50 mJy 4Normal Galaxies in Radio Continuum

M51 - Beck et al.

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VLA image atλ=90 cm

~45” resolutioninner few degrees

of the Galaxy

Our, nearly Normal, Galaxy 6An Active Galaxy

M87Jetdiscoveredby Curtisin 1918

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7An Active Galaxy

M87HST Image

M87 Distance = 15 MpcJet length = 2 kpc

8An Active Galaxy

M87HST Image

9Cygnus A – prototypical radio galaxy -- FR II

Carilli et al.

10Components of an AGN

Core

Lobe

Jet

Counter-Jet

Hot spot

“core” contains the central engine

30 kpc

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Clicker Question:

What is the ultimate energy source in anActive Galaxy?A: Nuclear fusion in stars.

B: Nuclear fission in stars.

C: Accretion of material onto a supermassive blackhole.

D: Direct conversion of matter into energy in the hotspots.

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Clicker Question:

The end of the Jet in a radio galaxy isusually marked with a:A: hot spot.

B: lobe.

C: core.

D: ‘X’

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13An Active Galaxy

3C31FR I

Laing et al.

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1 kpc

Taylor et al.

15Quasar 16BL Lac object

Giroletti et al2004

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VLBAImagesAt 5 GHz 30 pc

Pearson et al. 1981

Superluminalmotion

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19Apparent Velocity as a function of angle and intrinsic velocity 20

Evidence for limb brightened jet morphology on the parsec scaleis present in some FR I radio galaxies:1144+35, Mkn 501, 3C 264, M87, 0331+39…….

Velocity Structures

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Clicker Question:

Most compact jets are one-sided because:A: The jets are intrinsically one-sided (like a jet from ahose).

B: The jets are strongly beamed and one side ispointing closer to us.

C: On one side they are compressed as they run intomaterial in the interstellar medium.

D: Gravitational lensing by the supermassive blackhole.

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Clicker Question:

Some extragalactic jets have components thatappear to move faster than light (superluminalmotion). This happens because:A: Its an illusion because the jets are pointed at us andmoving close to the speed of light.

B: The jets come out of a black hole.

C: The jets are very light.

D: The jets are made of tachyons.

23Compact Symmetric Objects (CSOs) 24CSO Ages

Gugliucci et al. 2005

9/23 sources haveages < 500 years

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Peck & Taylor (2001)

Spectral index map from1.3/5 GHz VLBI observations

Free-free absorption in1946+708

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HI absorption in1946+708

Peck & Taylor(2001)

“Global” VLBIobservations

core:

M ~ 108 Msun

27Hydra A

Taylor (1996)

core:

M ~ 2 x 107 Msun

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NGC 4258NGC 4258

image courtesy Lincoln Greenhill(see Miyoshi et al 1995 Herrnstein et al 1999)

Can estimate central massCan estimate central mass

Considered best evidence ofConsidered best evidence of a supermassive black hole a supermassive black hole

Can estimate distance toCan estimate distance to host galaxy host galaxy

29Black Hole Mass - Velocity Dispersion

Kormendy et al.

30Accretion

v = (2GM/R)1/2

= c (Rg/R)1/2

L = 0.5 M c2 (Rg/R)

L = ε M c2

c = speed of light v = velocityR = object radiusRg = gravitational radiusε = efficiency

.*

ε = 3 x 10-4 for a white dwarf, 0.15 for a neutron starε up to 0.5 for a rotating black holeCompared to 7 x 10-3 for hydrogen fusion

Accretion is a very efficient energy source

.

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31 32

Clicker Question:

What is the most efficient energy sourcein the Universe?A: Fusion of hydrogen

B: Accretion onto a black hole

C: Coal-fired power plants

D: Wind turbines.

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Clicker Question:

What sources dominate the sky at radiowavelengths?A: Stars

B: Active Galaxies

C: Normal Galaxies

D: Globular clusters

34EGRET Gamma-Ray SkyGLAST

– EGRET (100MeV< E< 10GeV), 1991-1994– Diffuse Galactic plane emission + 271 sources– ~60 Blazars, ~6 Pulsars

GLAST (Launch in May 2008)– >30x EGRET sensitivity– Expect 4000-10,000 Blazars, >200 Pulsars

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Study ofAGN andMasers withUnprecedentedResolution for AstronomicalImaging

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• Japan-US VLBI Space Observatory 2

Launch in2012