Review of spiral, elliptical, irregular and lenticular galaxies
Unlike stars, galaxies aren’t born every day.
So we need to look back in time. The Hubble Deep Field.
Protogalactic clouds condense until first stars form.
Then galaxies form their halo (population II stars)
Elliptical Galaxies can form in these situations:
Interstellar gas can be stripped out if the galaxy flies through the center of a dense galaxy-cluster
NGC 2207 and IC 2163 and
can make elliptical galaxies (computer simulation model)
and momentarily irregular looking galaxies (example NGC 6240)
The biggest ellipticals are the galactic cannibals called Central Dominant Galaxies
The timeline shows many irregular galaxies early in Universe's history
Another test on the formation hypotheses
We can detect protogalactic clouds by their absorption of distant quasar light
Starburst galaxies = galaxies with very large star formation rates
Collisions can trigger a starburst
Cartwheel Galaxy and "intruder" galaxy
compare with waves in a pond
Even "close encounters" can trigger a starburst
Large Magellanic Cloud
locations of M81 and M82
M81 and M82
Example of tidal effect Earth tides
The underlying galaxy is almost always a spiral or irregular
exceptional case of elliptical galaxy NGC3928, in which the
central starburst resulted from the absorption of a small spiral galaxy ApJ
Starbursts can use up most or all of the gas in a galaxy,
This causes a lull in subsequent star formation as the
galaxy waits for its ISM to rebuild from stellar winds and SN
Many galaxies have had starburst episodes in their past
How would a galaxy that had a starburst 5 billion years ago look today?
Variations on the theme: Quasars, Seyfert galaxies, radio galaxies
example, visible light, redshifted
Discovery of Quasars (Quasi-Stellar Radio Sources) in 1960's
Absorption lines that were redshifted
Calculated velocity, distance, luminosity
Luminosity was huge
Bright in broad range of wavelengths: spectrum
Active Galactic Nucleus (AGN)
AGN = extremely bright center of a galaxy, where see galaxy, too Examples, NGC5548 vs normal galaxy NGC3277 , NGC 1068 = M77 Same spectra as quasars Can have jets, example: nucleus and jet of M87 Radio Galaxies and Jets Core-Jet-Lobe structure Examples: Cygnus A, 3C 353 Cartoon More examples: Centaurus A 3C 219 3C 31 NGC 1265 Compare Cygnus A with "Herbig Haro Objects" (jets from protostar) protostellar jets model is similar to radio galaxy model Radio Galaxies have molecular cloud donuts: Cartoon Radio Galaxies are really AGN viewed from different angle Where does the energy come from ? !! Material flowing into huge black hole in center Jets are material flowing along twisted magnetic field Cartoon Another cartoon of a supermassive black hole with accretion Finding the black hole mass from Kepler's 3rd law applied to orbits in accretion disk M87 Example
Nearby fainter ones are called Seyfert galaxies.
Quasars –strong emission lines, very redshifted, some are radio-loud
The power source - a supermassive black hole with accretion
Why do you need a black hole? It is 100 more efficient than fusion.
Do we have it right? Weighing supermassive black holes
radio galaxy model