Download ACTIVE GALAXIES

ACTIVE GALAXIES and
GALAXY EVOLUTION
Quasars,
Radio Galaxies,
Seyfert Galaxies and
BL Lacertae Objects
Immense powers emerging from
ACTIVE GALACTIC NUCLEI:
it’s just a phase they’re going through!
How do we observe the life
histories of galaxies?
Deep
observations
show us very
distant
galaxies as
they were
much earlier
in time
(Old light
from young
galaxies)
How did galaxies form?
We still can’t directly observe the earliest galaxies
Our best models for
galaxy formation
assume:
• Matter originally
filled all of space
almost uniformly
• Gravity of denser
regions pulled in
surrounding
matter
Denser regions
contracted, forming
protogalactic
clouds
H and He gases in
these clouds
formed the first
stars
Supernova
explosions from
first stars kept
much of the gas
from forming
stars
Leftover gas
settled into
spinning disk
Conservation of
angular
momentum
NGC 4414
M87
But why do some galaxies end up looking so different?
Why do galaxies differ?
Why don’t all galaxies have similar disks?
Conditions in Protogalactic Cloud?
Spin: Initial angular momentum of protogalactic cloud
could determine size of resulting disk
Conditions in Protogalactic Cloud?
Density: Elliptical galaxies could come from dense
protogalactic clouds that were able to cool and form
stars before gas settled into a disk
Elliptical vs. Spiral Galaxy
Formation
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.
• Sometimes see shells of stars around Es
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
• Collision Simulation Movie
Collisions
may explain
why
elliptical
galaxies
tend to be
found where
galaxies are
closer
together
Giant elliptical
galaxies at
the centers of
clusters seem
to have
consumed a
number of
smaller
galaxies
Starburst
galaxies are
forming
stars so
quickly they
would use
up all their
gas in less
than a
billion years
4 MAIN CLASSES of AGN
•
•
•
•
Radio Galaxies
Quasars
Seyfert Galaxies
BL Lacertae Objects (or Blazars with some
Quasars and some Radio Galaxies)
• All are characterized by central regions with
NON-THERMAL radiation dominating over
stellar (thermal) emission
Thermal vs. Non-Thermal Spectra
Normal mostly from stars,
Active mostly synchrotron
RADIO GALAXIES
• All are in Elliptical galaxies
• 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.
• Head-tail radio galaxies arise when jets are bent by
the ram-pressure of 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
Radio Lobes Dwarf Big Galaxy
Core Dominated RG (M86)
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 (2008) convincing
record redshift is z = 6.4, i.e., light emitted in
FAR UV at 100 nm is received by us in the
near IR at 740 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
• QUASARS are AGN: surrounding galaxies
detected, though small nucleus emits
10-1000 times MORE light than 1011 stars!
“Brighter than a TRILLION suns”
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
Radio Loud Quasar, 3C 175
Thought Question
What can you conclude from the fact that quasars
usually have very large redshifts?
A.
B.
C.
D.
They are generally very distant
They were more common early in time
Galaxy collisions might turn them on
Nearby galaxies might hold dead quasars
Thought Question
What can you conclude from the fact that quasars
usually have very large redshifts?
A.
B.
C.
D.
They are generally very distant
They were more common early in time
Galaxy collisions might turn them on
Nearby galaxies might hold dead quasars
All of the above!
Birth of a Quasar Movie
• Fast
variability
implies
small size
• Immense
powers
emerging
from a
volume
similar to
the solar
system!
SEYFERT GALAXIES
• Sa, Sb galaxies with BRIGHT, SEMI-STELLAR
NUCLEI
• NON-THERMAL & STRONG EMISSION LINES
• VARIABLE in < 1 yr  COMPACT CORE
• Type 1: Broad Emission lines (like QSOs), strong in
X-rays
• Type 2: Only narrow Emission lines, weak in X-rays
• 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)
• OR 10% of S's are Seyferts for about 10% of the time
(or any other combination of fraction and lifetime)
A Seyfert and X-ray Variability
• Circinus, only 4 Mpc away; 3C 84
More About Seyferts
• Seyferts are 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
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 ARE OFTEN CALLED BLAZARS
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 (=Mdot) 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
• L = G MBH Mdot / R,
• with R the main distance from the Super Massive
Black Hole (SMBH) where mass is converted to
energy.
Time Variability
•
•
•
•
•
tVAR = R / c
tVAR = 104 s 
R = 3 x 1014 cm = 10-4 pc
For L = 1047 erg/s,
M_dot = 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.
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
• Disks have been seen via MASERS in some
nearby Seyfert AGN.
• VLBI: radio jets formed within 1 pc of center.
• There are several other more technical lines
of evidence also supporting the SMBH
hypothesis for AGN.
Rapidly Rotating Gas in M87 Nucleus
M87 zoom toward black hole
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
SMBH Model for AGN
UNIFIED MODELS FOR AGN
• Three main parameters: MBH;
the accretion rate, M_dot, and
viewing angle to the 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_dot:
•  small: QSO is seen
including AD and BLR
•  large: only NLR plus
radiating torus: seen as
UltraLuminous InfraRed
Galaxies (ULIRGs)
• Low MBH, M_dot:
•  small: Seyfert Type 1
 big: Seyfert Type 2
• RADIO LOUD (Jets)
• High MBH, M_dot:
•  very small: Optically Violently
Variable Quasar
•  small: radio loud quasar
(QSR)
•  large: classical double radio
galaxy (FR II type)
• Low MBH. M_dot:
•  very small: BL Lac object
•  small: broad line radio galaxy
(FR I type)
•  large: narrow line radio
galaxy
Different AGN from Different Angles
Luminous: Quasars seen
close to perpendicular to
disk and Ultraluminous
Infrared Galaxies near
disk plane
Weaker: Type 1 or Type 2
Seyferts
If jets are important:
BL Lacs along jet axis,
Quasars at modest
angles & Radio Galaxies
at larger angles
Black Holes in Galaxies
• Many nearby galaxies – perhaps all of them –
have supermassive black holes at their
centers
• These black holes seem to be dormant active
galactic nuclei
• All galaxies may have passed through a
quasar-like stage earlier in time
Galaxies and Black Holes
• Mass of a
galaxy’s
central
black hole is
closely
related to
mass of its
bulge