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

But why do some galaxies end up looking so different?

M87NGC 4414

Why do galaxies differ?

Why don’t all galaxies have similar disks?

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

Conditions in Protogalactic Cloud?

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. They are generally very distantB. They were more common early in timeC. Galaxy collisions might turn them onD. Nearby galaxies might hold dead quasars

Thought Question

All of the above!

What can you conclude from the fact that quasars usually have very large redshifts?

A. They are generally very distantB. They were more common early in timeC. Galaxy collisions might turn them onD. Nearby galaxies might hold dead quasars

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 AnglesLuminous: Quasars seen close to perpendicular to disk and Ultraluminous Infrared Galaxies near disk planeWeaker: Type 1 or Type 2 Seyferts

If jets are important:BL Lacs along jet axis,Quasars at modest angles & Radio Galaxies at larger angles

• 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

Black Holes in Galaxies

Galaxies and Black Holes

• Mass of a galaxy’s central black hole is closely related to mass of its bulge