Presentation on theme: "ACTIVE GALAXIES and GALAXY EVOLUTION Quasars, Radio Galaxies, Seyfert Galaxies and BL Lacertae Objects Immense powers emerging from ACTIVE GALACTIC NUCLEI:"— Presentation transcript:
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? M87 NGC 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 '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 )
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 times MORE light than 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 distant B. They were more common early in time C. Galaxy collisions might turn them on D. 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 distant B. They were more common early in time C. Galaxy collisions might turn them on D. 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 erg/s (10 41 W) 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 M BH Mdot / R, with R the main distance from the Super Massive Black Hole (SMBH) where mass is converted to energy.
Time Variability t VAR = R / c t VAR = 10 4 s R = 3 x cm = pc For L = erg/s, M_dot = 10 M /yr we get M BH = 3 x 10 8 M and R S = 9 x cm So, R = 3 R S 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: M BH ; the accretion rate, M_dot, and viewing angle to the accretion disk axis, Main ingredients: SMBH > 10 6 M pc < accretion disk < 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 < 10 2 pc to maybe 10 6 pc!)
Unification for Radio Quiet and Radio Loud RADIO QUIET High M BH, M_dot: small: QSO is seen including AD and BLR large: only NLR plus radiating torus: seen as UltraLuminous InfraRed Galaxies (ULIRGs) Low M BH, M_dot: small: Seyfert Type 1 big: Seyfert Type 2 RADIO LOUD (Jets) High M BH, M_dot: very small: Optically Violently Variable Quasar small: radio loud quasar (QSR) large: classical double radio galaxy (FR II type) Low M BH. 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
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