Active Galactic Nuclei

Ay 16, April 8, 2008

AGN

DEFINITION

PROPERTIES

GRAVITATIONAL LENSES

BLACK HOLES

MODELS

WHAT IS AN AGN?Objects that emit significant amounts of

radiation from non-thermal sources

(i.e. not stars or dust or thermal gas).

In order of discovery:

Seyfert Galaxies

Radio Galaxies

Quasars

BL Lac Objects

LINERS (Low Ionization Emission Regions)

Early History

Carl Seyfert & strange emission line galaxies (1943)

Birth of Radio Astronomy & discovery of strong sources = radio galaxies (40-50’s)

Greenstein & Schmidt & QSO’s (1963)

Surveys of Extremely Blue Objects (60-70’s)

Surveys at other Wavelengths (70’s > )

SY1

AGN

Spectra

SY2

QSO

Mean UV QSO Spectrum

LBQSO Spectrum

NGC 4151

Typical

SY1

Seyfert 1 galaxy and quasar spectra are dominated by broad line regions, lines often showing doppler velocities of 0.1c

Seyfert 2 galaxies spectra are dominated by narrower lines, ~ 1-2000 km/s wide

LINER spectra are dominated by stars plus emission lines from multiple ionization states indicative of non-thermal excitation

BL Lac spectra show almost no features but strong continua

M87 Core

In

X-rays

Markarian 231

Markarian 421

BL Lac in an E Galaxy

TeV Source

•

BL LAC

SED’s

Radio Galaxies

M87 = Virgo A

M87 in the Radio

(VLA)

M87

Central

Jet

M87

Jet

In 3 bands

Centaurus

A

Radio on

Optical

Image

Cygnus A (VLA Conway & Blanco)

Synchrotron Power

= related to kinetic enegy of electron

= (1 - (v/c)2)-1/2 = (1 - 2)-1/2

where = v/c

Synchrotron Spectra

Baldwin, Phillips

& Terlevich

AGN

LINERS

NORMAL

Ly Alpha Forest

Eddington LuminosityLargest Luminosity that can pass through

a gas in hydrostatic equilibrium :

Outward Force of Radiation Pressure

> Inward Force of Gravity

Gravity dP/dr = -g = -GM/r2

Luminosity dP/dr = -(T/mpc) (L/4r2)

T = Thomson Cross section

LEdd = 4GMmpc/T

= 3.3 x 104 L(M/M)

Gravitational Lensing

Deflection of Light passing at a distance b by an object of mass M:

= 4GM/bc2

Bending of light by the Sun:

r = 6.96 x 1010 cm M = 1.989 x 1033 g

= 8.47 x 10-6 radians = 1.74”

Gravitational lensing:

2237+0305 = Einstein’s Cross

Gravitational Redshift

Photons lose E as the move out of a gravity well.

For a photon E = hc/, “m” = E/c2 = h/c Gravitational Potential E = -GMm/r

E = -GMh/cr

/ = GM/rc2

which generally is pretty small except for NS and BH

Black Holes

Curvature around a point mass has a critical radius = Schwarzchild Radius

Inside this is a singularity

RS = 2GM/c2

In units we know

RS = 3.0 km (M/M)

Gravitational redshift from RS =

NGC 4261 X-ray vs Optical

V = 1100 km/s

M87’s central mass:

Given the HST observations, what’s the enclosed mass?

v = 1100 km/s ~ 1” D = 16.1 Mpc

R = 0.078 kpc (78 pc)

GMm/R = 1/2 mV2 for circular orbits

M = 0.5 V2R/G

G = 4.309 x 10-6 kpc (km/s)2 / M

Mcore ~ 1010 M

Reverberation Mapping

NGC5548

Lag ~ 20 days Size ~ 20 light days ~ 0.02 pc

Maggorian Relation (Nuker team)

Almost every large galaxy has a central BH, and the BH mass is directly correlated with the galaxy’s total bulge mass!

A Unified Model of AGN’s

We have come to believe that all AGN are essentially driven by the same phenomena --- a central black hole surrounded by an accretion disk, hot clouds of gas and dust. The disk is hot, 105 K plus. The AGN is powered by accretion onto the BH.

And what you actually see is driven by the viewing angle.

Unified AGN ModelBH + Disk + Torus

SY2 SY1 BL Lac

edge on tilted down the pipe