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!

First: Copernican Principle, Expanded VERY IMPORTANT POINT: The expansion of the Universe shown by the Hubble Law should be independent of location in the Universe. EVERYONE WOULD SEE AN EQUIVALENT EXPANSION AWAY FROM THEM. In other words, we do not believe we are at a “special” place in the universe.

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? 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 Stat here on 4/14

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, 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 Start here on 11/12