Active Galactic Nuclei Ay 16, April 8, 2008. AGN DEFINITION PROPERTIES GRAVITATIONAL LENSES BLACK...
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Transcript of Active Galactic Nuclei Ay 16, April 8, 2008. AGN DEFINITION PROPERTIES GRAVITATIONAL LENSES BLACK...
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