Transcript ACTIVE GALACTIC NUCLEI and UNIFICATION SCHEMES Paul J. Wiita

ACTIVE GALACTIC NUCLEI
and UNIFICATION SCHEMES
Paul J. Wiita
Georgia State University, Atlanta, USA
Winter School on Black Hole Astrophysics
APCTP, Pohang, January 17-20, 2006
Outline
• Observational classification: peculiar vs.
active galaxies
• Key properties of different AGN classes
• Fundamental reasons for SMBH model
• Microvariablity of Different AGN types
• Unification schemes for AGN
Start with the Mildly Active or
Peculiar Galaxies
• STARBURST galaxies -- 100's of stars forming per
year, but spread over some 100's of parsecs.
• Other PECULIAR galaxies involve collisions or
mergers between galaxies.
• Sometimes produce strong spiral structure (e.g. M51,
the "Whirlpool")
• Sometimes leave long tidal tails (e.g. the "Antennae"
galaxies)
• Sometimes leave "ring" galaxy structures--an E
passing through a S.
Peculiar Galaxies: Starburst (NGC 7742) , Whirlpool (M51),
Antennae (NGC 4038/9) in IR, Ring (AM 0644-741)
Colliding Galaxies
• “Cartwheel” ring galaxy
• Antennae, w/ starbursts
and a simulation: a
collision in progress
4 MAIN CLASSES of REAL AGN
•
•
•
•
Radio Galaxies
Quasars
Seyfert Galaxies
BL Lacertae Objects (now more often called
Blazars with some Quasars included)
• All are characterized by central regions with
NON-THERMAL radiation dominating over
stellar (thermal) emission
Thermal vs. Non-Thermal Spectra
Normal galaxy spectra arise from stars,
AGN mostly synchrotron and inverse Compton
RADIO GALAXIES
• All (nearly) are in Elliptical galaxies, usually giant Es
• Two oppositely directed JETS emerge from the
galactic nucleus
• They often feed HOT-SPOTS and and LOBES on
either side of the galaxy
• Radio source sizes often 300 kpc or more --- much
bigger than their host galaxies’ optical extents.
• Head-tail and wide-angle-tail radio galaxies arise
when jets are bent by the ram-pressure of ICM/IGM
gas as the host galaxy moves through it.
• For powerful sources only one jet is seen: this is
because of RELATIVISTIC DOPPER BOOSTING:
the approaching jet appears MUCH brighter than an
intrinsically equal receding jet since moving so FAST;
• Can yield CORE DOMINATED RGs
Radio Galaxy: Centaurus A
Cygnus A and M87 Jet
M87 on all
Scales
1.3cm VLBI
down to 0.07 pc
(~100 RS) while
90 cm VLA
shows bubbles
out to 70 kpc
Radio Lobes Can Dwarf Big Host Galaxies
• Fornax A, about 400 kpc across
• 3C 296, about 150 kpc across (VLA images)
Fanaroff-Riley Classification
• FR I RGs (M87) are
weaker and have the
peak of their flux from the
inner portion (often jet or
plume dominated) 3C 31
(VLA 20 cm)
• FR II RGs (most
previous) are more
powerful, possess hotspots and dominated by
the extended lobes
• LR from 1041 to 1046 erg/s
More FR I RGs:
3C75; 3C449; 3C83.1 (at 6 and 20 cm from VLA)
Ledlow-Owen Relation & FR II/I
• Greater radio luminosity needed to make an FR II if
the jets emerge from a more luminous host galaxy
• Probably implies many FR II’s turn into FR I’s if they
entrain too much gas and slow from relativistic speeds
Core Dominated RG (M86)
Doppler Boosting and Apparent Velocity
• Dramatic increases in observed flux density if jet has
high v = c and small l-o-s angle, .
• Superluminal apparent transverse velocities also
seen frequently in VLBI measurements of knots
Sobs( )   3 Sem ( )
1

(1  cos )
1


S(

)

v
(1  2 )1/ 2
 sin 
 app 
(1  cos )
Doppler factor, 
Lorentz factor,  and
spectral index,
Exponent = 3 for knots,
2 for continuous flow
QUASAR PROPERTIES
• QUASI-STELLAR-OBJECT: (QSO): i.e., it
looks like a STAR BUT: NON-THERMAL
SPECTRUM UV excess (not like a star)
• BROAD EMISSION LINES  Rapid motions
• VERY HIGH REDSHIFTS  not a star, but
FAR away. The current (2005) convincing
record redshift is z ~ 6.5, i.e., light emitted in
FAR UV at 100 nm is received by us in the
near IR at 750 nm
• HUGE DISTANCES  VERY LUMINOUS
“NEWER” QUASAR
DISCOVERIES
• Only about 10% are RADIO LOUD
• Most show some VARIABILITY in POWER
• OVV (Optically Violently Variable) QUASARS
change brightness by 50% or more in a year
and are highly polarized (> 3% linear in
optical)
• QUASARS are AGN: surrounding galaxies
detected, though small nucleus emits
10-1000 times MORE light than 1011 stars!
“Brighter than a TRILLION suns”
• Lbol > 1046 erg/s would qualify as a quasar
Quasar 3C 273
• Radio loud
• Rare OPTICAL
jet, but otherwise
looks like a star
• Relatively nearby
quasar
Redshifted Spectrum of 3C 273
Typical Quasar Appearance
• Most are
actually very
faint
• BUT their huge
redshifts imply
they are billions
of light-years
away and
intrinsically
POWERFUL
Quasar Host Galaxies
• Even by z ~ 3
many
QSOs were in
forming galaxies
with multiple
components
• Most quasar host
galaxies have
MB<-23 and
are extremely
luminous
themselves
Radio Loud Quasar, 3C 175
Most quasars do vary
with most changing
noticeably over the
course of a year or
less.
These rapid variations
imply small sizes.
Immense powers
emerging from a
volume smaller than
the solar system.
Quasar Emission Lines
• Broad emission lines have FWHM > 5000 km/s
• Usually have narrow cores w/ FWHM < 2000 km/s
• Diagnostics of T and density, implying TBLR  15000 K
and 108 < n < 1012 cm-3 for BLR
• Breadth implies lines form from rapidly moving gas:
clouds at < 1 pc from core, ~random or in disk wind
• Lower ionization state of NELs implies at much greater
distance from the ionizing core of AGN: ~100 pc
• Locations of BLR and BH mass can come from
reverberation mapping; line variability lags continuum
SEYFERT GALAXIES
• Sa, Sb galaxies (sometimes S0) with BRIGHT, SEMISTELLAR NUCLEI
• NON-THERMAL & STRONG EMISSION LINES
• VARIABLE in < 1 yr  COMPACT CORE
• Type 1: Broad Emission lines (like QSOs), strong in
X-rays; LX > 1043 erg/s
• Type 2: Only narrow Emission lines, weaker in optical
continuum and X-rays; LX > 1041 erg/s (observed)
• Occasionally one type evolves into another over a few
years -- indicative of viewing along edge of screen
• Type 2 are 2 to 3 times more common than Type 1
LIFETIMES OF SEYFERT
GALAXIES
• About 1% of all Spirals are SEYFERTS, so
• Either 1% of all S's are always Seyferts OR
• 100% of S's are Seyferts for about 1% of the time
(MORE LIKELY; active lifetimes ~108 yr )
• OR 10% of S's are Seyferts for about 10% of the time
(or any other combination of fraction and lifetime)
A Seyfert and Variability
• Circinus, only 4 Mpc away; 3C 84
More About Seyferts
• Seyferts are usually
weak radio emitters.
• CONCLUSIONS
ABOUT SEYFERTS
Fundamentally, they
are WEAKER QSOs
• Type 1: we see the
center more directly
Type 2: dusty gas torus
blocks view of the
center and more
reradiated IR is seen
BL Lacertae Objects
• NON-THERMAL SPECTRUM: Radio through X-ray
(and gamma-ray)
• Radiation strongly POLARIZED
• HIGHLY VARIABLE in ALL BANDS
• But (when discovered) NO REDSHIFT, so distances
unknown
• Later, surrounding ELLIPTICAL galaxies found
• CONCLUSION: greatly enhanced emission from the
AGN due to RELATIVISTIC BOOSTING of a JET
pointing very close to us.
• BL Lacs + OPTICALLY VIOLENTLY VARIABLE
QUASARS + HIGHLY POLARIZED QUASARS ARE
OFTEN CALLED BLAZARS
Optical Monitoring: Blazar Light Curve
AGN CONTAIN SUPERMASSIVE
BLACK HOLES (SMBHs)
• KEY LONGSTANDING ARGUMENTS:
• ENERGETICS: Powers up to 1048 erg/s (1041W)
Even at 100% efficiency
would demand conversion of

about 18 M /yr ( M) into energy.
• Nuclear processes produce < 1% efficiency.
• GRAVIATIONAL ENERGY via ACCRETION can

produce between
6% (non-rotating BH) and 32%
(fastest-rotating
BH),and the Luminosity is crudely

• L = G MBH M/ R,
• with R the main distance from the Super Massive
Black Hole (SMBH) where mass is converted to

energy.
Reminder: Orbits around BHs
• GR gives rise to an effective potential which yields
orbits depending on the energy and angular
momentum of the matter near a BH
• Once beyond about 50 Rs orbits are ~ Newtonian
• Unlike Newtonian case we find an innermost stable
orbit at Rms=3Rs = 6GM/c2 for Schwarzschild BH
There is also the last possible, or marginally bound,
orbit at Rmb=2Rs (where accretion efficiency = 0)
• A pseudo-Newtonian potential: =GM/(r-RS)
reproduces the above results (Paczynski & Wiita)
• If we look for orbiting photons, instead of massive
particles, there is a last stable orbit at Rph=1.5Rs

Kerr(-Newman) Black Holes
• Rotating BH: key results are the presence of a static
limit, inside of which one must co-rotate with the BH
• The horizon moves further inward the faster the BH
spins. This implies Rms and Rmb also move inward.
• The amount of binding energy that is extracted from
infalling matter goes up from <0.06 to ~0.42 m(c2)
rstatic( )  M  M 2  Q2  a 2 cos 2 
r  M  M 2  Q2  a 2  M(G /c 2 ) as a  M
Cosmic censorship hypothesis:
a < M so no naked singularities exist
Time Variability
•
•
•
•
•
tVAR = R / c
tVAR = 104 s 
R = 3 x 1014 cm = 10-4 pc
For L = 1047 erg/s,

M = 10 M /yr we get MBH = 3 x 108 M and
RS = 9 x 1013 cm
• So, R = 3 RS
• MUTUALLY CONSISTENT POWERS AND
TIMESCALES.
Big Blue Bump in QSO SED
• This peak is commonly seen in the blue/Near UV
(restframe) for quasars and is nicely modeled by the
quasi-thermal emission from a disk accreting at
substantial rates (T~50,000 K): composite of ~2200 (!)
SDSS quasars (Vanden Berk et al 2001)
RECENT OBSERVATIONAL
SUPPORT
• The Hubble Space Telescope has revealed
that star velocities rise to very high values
close to center of many galaxies and gas is
orbiting rapidly, e.g. M87, but dozens of cases
now known
• Disks have been seen via MASERS in some
nearby Seyfert AGN.
• VLBI: radio jets formed within 1 pc of center,
as seen earlier for M87.
Rapidly Rotating Gas in M87
Nucleus
Direct Evidence for Rotating Disk
Masers formed in warped
disk in NGC 4258 (and a
few other Seyfert galaxies)
Evidence for Supermassive Black Holes
NGC 4261: at core of radio emitting jets is a clear disk
~300 light-yrs across and knot of emission near BH
Similar Optical Microvariability in
Radio Quiet QSOs and Blazars?
• Lots of debate about RQQSOs: some claimed fairly frequent
detections of INOV (e.g. de Deigo et al. 1998); others say no (e.g.
Rabette et al. 1998; Romero et al. 1999) but temporal sampling
and/or sensitivity and/or comparison choices were inadequate
• We claim the first convincing evidence for such optical INOV in
true radio “silent” quasars (Gopal-Krishna et al. 2003; Stalin et al.
2004a,b; Sagar et al. 2004)
Observations mostly at 104cm telescope, Nainital, India
• Both duty cycle and amplitude are lower in RQQSOs than for
blazars; but differences between RQQSOs and radio-loud
quasars (and even low-polarization core-dominated quasars)
are small in our matched sets of 6 or 7 of each type of AGN
• Differences observed can arise from simple Doppler boosting
RQQSO INOV
BL Lac INOV
Radio-Loud Lobe Dominated Quasar INOV
Comparison of RQQ and BL Lac INOV
• Duty cycles for low amplitude variations are very
similar, around 20%
• High amplitude variations: all BL Lac
Comparison of CDQ and BL Lac INOV
• Low polarization CDQs
have properties similar
to RQQs and LDQs,
with duty cycles of
10-25% when
observed for > 4 hours
• High polarization CDQ
is similar to BL Lacs,
with duty cycles >50%
Doppler
Boosting
Factors
• Typical INOV amplitude
from blazar at small
angle is converted to
lower amplitude and
longer timescale at
larger viewing angles
and would appear just
like RQQSO
INOVsimilar
mechanism.
• Is an optically emitting
jet always present?
• Do disk perturbations
get amplified in a jet?
SMBH Model for AGN
Most (all?) Galaxies Have Central SMBHs
Roughly, SMBH mass
is 0.003 of the BULGE
mass;
for ellipticals, the bulge
mass is the entire star
mass; for most spirals,
just a fraction.
So BH and galaxy
probably grow up
together.
Better correlation with
bulge velocity
dispersion or perhaps
galactic potential
energy.
Wide Span of SMBH Mass vs Galaxy
Velocity Dispersion
• Compiled by Greene &
Ho -- includes active
and inactive galaxies
• MBH = f R V2/G with
f=0.75 for spherical BLR
• RBLR  L51000.64
• V from FWHM(H)
• Best fit: M  3.65 for all
while M  4.02 for
inactive only
Unification through Orientation
• For Seyferts: scattered BL and continuum can
be seen in polarized light for Type 2’s
(Antonucci & Miller)
• For RGs: quasars are shorter than similar
powered and redshifted FR IIs (Scheuer;
Barthel; Gopal-Krishna et al)
• FR I RGs are statistically the parent
population of BL Lacs for the BL Lacs w/in a
few degrees of l-o-s (Padovani & Urry)
Seyferts and Unification
• Narrow line spectrum of Seyfert 2
• But, when polarized radiation observed, broad lines,
scattered by electrons are also visible
• Also explains much lower x-ray and continuum in Sy2
UNIFIED MODELS FOR AGN

• Three main parameters: MBH, M , and
viewing angle to the BH and accretion disk
axis, 
• Main ingredients:

• SMBH > 106 M
• ~10-5 pc < accretion disk < ~10-1 pc (AD)
• broad line clouds < 1 pc (BLR)
• thick, dusty, torus < 100 pc
• narrow line clouds < 1000 pc (NLR)
• sometimes, a JET (usually seen from < 102 pc
to maybe 106 pc!)
Unification for Radio Quiet and Radio Loud
• RADIO QUIET

• High MBH, M :
•  small: QSO is seen
including AD and BLR
• 
large: only NLR plus
radiating torus: seen as
UltraLuminous InfraRed
Galaxies (ULIRGs)

• Low MBH, M :
•  small: Seyfert Type 1
 big: Seyfert Type 2

• RADIO LOUD
(Jets)

• High MBH, M :
•  very small: Optically Violently
Variable Quasar
• 
small: radio loud quasar
(QSR)
•  large: classical double radio
galaxy (FR II type)
• Low MBH. M :
•  very small: BL Lac object
•  small: broad line radio galaxy
(FR I type)

•  large: narrow line radio
galaxy
Different AGN from Different Angles
If jets are important:
BL Lacs (and OVVs)
along jet axis,
RLQSO at modest angles
& Radio Galaxies at
larger angles
No jets: Luminous:
Quasars seen close to
perpendicular to disk and
Ultraluminous Infrared
Galaxies near disk plane
Weaker: Type 1 or Type 2
Seyferts
Key Conclusions
• AGN make up a small fraction of galaxies
at any given time, though all may have
undergone such a phase when young
• SMBHs provide the ultimate energy
source for AGNs (masses 106 to >109M)
• The zoo of AGN types can be tamed
through unified schemes (though
complications, such as critical angle rising with
central luminosity are probably needed)