Download Quasars and Active Galactic Nuclei

Quasars and Active Galactic Nuclei
Type 2
Just narrow emission lines
Seyfert Galaxies
• Carl Seyfert, 1940’s
• Spirals
• Very bright unresolved nucleus
• Strong emission lines
• High ionization states
• Broad lines = large internal velocity dispersion
• 10,000 km/s
N+
O++
O+
Type 1
Broad + narrow
emission lines
Fe+6
Ne+4
3
2
1
NGC 1097
H
Gemini J-band image
+ diffraction ring??
H
H
H energy levels
Quasars
• Luminosity = (apparent brightness) x distance2
• Apparent brightness:
• Discovered quasars from their radio emission.
Orion
nebula
Radio
position
3C 273
• But… which object???
Apparent brightness 
redshift = 0
Quasar
3C 273
Redshift = 0.158
Parkes, Australia … 210’ radio
telescope.
• Distance: Now measure optical spectrum
Wavelength 
• Doppler shift of wavelength of light
 velocity of recession (redshift) due to expansion of Universe.
 huge distance  huge luminosity!
1
Classification
• Quasar = Quasi Stellar Radio Source
• QSO = Quasi Stellar Object
• radio-quiet
• 1000’s of times more numerous than Quasars
Active
Galactic
Nuclei
(AGN)
• Blazars (or BL Lac objects)
•
bright continuum source, but no emission lines
• Seyfert Galaxies
• Types 1 and 2
• Radio galaxies
• etc
Visible
X-ray
Radio
Cygnus A
Blackbody
Defining feature = non-thermal continuum
• Strong in Quasars, QSOs
• Weaker in Seyferts, radio galaxies
Measured Properties
Rapid brightness changes
(weeks, days. hours).
[CO Fig. 28.16]
QSOs are most
luminous objects
in universe on
107 yr timescales.
Not
detectable
[CO Fig. 28.19]
3C 273
Time 
 Size = light-weeks,
light-days, light-hours.
In centers of
galaxies
HST images
2
Most Quasars Lived and Died Long Ago
Star Formation Rate Density 
5.9
 time
2.2 1.6
0.8 Gyr since Big Bang
Hopkins & Beacom
2006, ApJ, 651,
142
 time
[CO Fig 28.17]
Number of Quasars
per unit volume
3.3
Rate at which stars are
formed in galaxies.
(corrected for reddening)
Observations show:
QSO
density
•
•
•
•
 time
 time
huge luminosity
from a tiny volume
at centers of galaxies
happened early in history of galaxies
What are they?
• Gas, stars fall into 106-108 Msun black hole.
• Grav. energy is released
[Fig 28.23]
[Fig 28.24]
[Fig 28.25]
•
•
•
•
•
Black hole
Accretion disk
Broad emission-line region
Obscuring torus
Narrow emission-line region
3
Viewing Angle Effects
Blazar or “BL Lac” object:
• Special-relativistic beaming
Continuum made vastly brighter .
• So only continuum is seen,
Type 1:
3
2
[Fig 28.25]
Broad + narrow emission lines
+ non-thermal continuum
1
Type 2:
Just narrow emission lines
The Source of the
Luminosity:
• Matter falls onto
accretion disk.
[Fig 26.17]
Accretion disk +
Black Hole Black Hole + Jets
4
Notation:
No G, no c
Spinning Black Holes
dd cross term  “frame dragging”
Kerr metric (1963)
where
J = Angular Momentum
Maximal spin: Jmax = M2
•
•
[CO 17.22]
(or = GM 2/c2 in CO units)
Usually ~ the case.
Then Event Horizon in equatorial plane is at
“Static limit”
Frame-dragging  c
Ergosphere
r=M

Infalling particle with no angular momentum:
r = 2M
[TW2, pg. F-14]
E/m
r = M+(M 2-a2)1/2
Remaining energy
(rest radiated away)
(unrealistic case with unstable
orbits, but gives an estimate
of available energy)
r/M
Both plots for equatorial plane only
The Special Case of Kerr (Rotating) Black Holes:
Direct Magnetic Coupling by the BZ Effect
BZ
PC
7
•
•
•
BP
Blandford
(2001; 2003)
Accreting plasma presses magnetic field onto Kerr hole
Magnetic field lines temporarily thread Kerr hole
Field extracts rotational energy and angular momentum
from hole
LBZ ~ 1046 erg s 1 m9 m j 2
 BZ  ?????
( From Meier & Nakamura
http://www.atnf.csiro.au/education/workshops/jaunceyfest/Talks/19.Da
vidMeier/Meier_DJ65.ppt)
Blandford & Znajek (1977)
5
Accretion Disks
Disk material loses energy
by black body radiation
Accretion
disk
L( r )  T ( r )4  2r dr 
[CO pgs. 661-665]
T ( r )  r 3 / 4
 total radiation = sum of black bodies.
•
Well-studied phenomena in
local binary star systems
•
Angular momentum 
material cannot fall directly
onto central mass.
Binary stars  “thin” accretion
disks
•
•
Material works its way in
toward center due to viscosity.
For QSO: Material eventually
falls into Black Hole
•
r
hotter
cooler
5
[Fig. 18.13]
4
Luminosity 
•
“cataclysmic variables”
log T (K) 
•
[Fig. 18.14]
From innermost stable orbit
log r 
log  (nm) 
Binary star results, but QSOs are similar.
Iron K profiles
X-ray emission line.
From inner electron shell.
Actual data
Colors indicate
wavelength shift
Changing inclination
Schwarzschild
Redshifted
Blueshifted
Frequency 
Wavelength
Fabian et. Al., 2000, PASP, 112, 1145
Kerr
Line of sight
Rotating vs. non-rotating
6
Continuum Source
Thermal
radiation
from dust
X-rays from
“inverse Compton scattering”
Thermal ra
d. from dis
k
Log  F 
Cloud of relativistic electrons
Thermal
radiation
from disk
X-rays from
“inverse
Compton
scattering”
Synchrotron
radiation
from jet
[Fig. 28.23]
[Fig. 28.4]
Log frequency 
Energetics
• Accretion rate & luminosity.
• mass falls into black hole:
Ldisk  
• Eddington limit.
• Radiation pressure = gravity:
.
dM 2
c  M c 2
dt
LEdd
GmM BH
m 
4r 2
4r 2
absorption
cross-section
  0 .1
.
M  1  10 M yr-1
Luminous QSOs:
L ~ LEdd
Seyferts, Radio Galaxies:
L << LEdd
7