Galaxy Formation Formation of galaxies in cold dark matter universe

Hubble Galaxy Sequence Ellipticals (round through oval) Spirals (centrally condensed with arms) Barred Spirals (distinct bar shape with bulge)

Shapes of Galaxies Spirals disk shaped with spiral arms often have bright bulges in center contain interstellar gas, nebulae, star forming regions, open clusters and globular clusters Barred Spirals spiral arms emerge from end of bar gas from outer part of galaxy funneled to center through the bar, forming new stars in bulge

Shapes of Galaxies Ellipticals range from spherical to foot-ball shapes lots of old stars and globular clusters star formation is over or just restarting maybe the result of collision and merger of smaller galaxies Irregulars lots of gas and new stars forming rather small compared to spirals and ellipticals

Edge-on Spiral Galaxy NGC we think our Galaxy looks like this This is an infrared composite image from KPNO

Spiral sequence SandageHubble Space Telescope NGC 7537/Sbc

Spiral Galaxies Bulges formed over a short period very early in the young universe, perhaps through the collapse of a single cloud of hydrogen or merger of primeval star clusters. NGC 1232/VLT NGC 1288

Spiral sequence SandageHubble Space Telescope NGC 5838/S0

Spiral sequence SandageHubble Space Telescope NGC 5689/Sa

Barred Spiral M61 Bar across central region is made of stars, gas, and dust Small bulge is dominated by a disk of material Spiral arms begin at both ends of the bar The bar is funneling material into the hub, which triggers star formation and feeds the bulge

Barred Spiral NGC1365 Optical/Sandage Optical/HST WFPC2 IR/HST NICMOS

M87 Optical Giant elliptical galaxy At center of Virgo cluster Many globular clusters surround it Little dust and gas in the galaxy 50 million light years away

M87 Optical Jet HST IR and UV composite Globular clusters also seen Note shock waves and knot patterns in jet Bright point at central black hole

Irregular Galaxies NGC 4753/I0 Sextans A 5000 light years across 5 million light years away

Galaxy Evolution A computer simulation of a flat disk-type galaxy colliding with a dwarf galaxy. The dwarf galaxy cannot be seen, but its gravitational influences trigger the production of spiral arms in the gas-rich disk.

Collisions and Mergers Note: galaxies do not make noise when they collide!

Galaxy Collision

Galaxy Collisions, Part 2

M31/Andromeda Our nearest spiral neighbor 2 million light years away Center of M31 has two optical nuclei

M31/Chandra X-ray Image of central part of our neighbor M31 Bright X-ray sources are binaries with black holes or neutron stars Central BH is very cool, 30 million M o Center of M31

Cartwheel Galaxy Wheel shape was formed from collision of two galaxies Bright stars are forming at the edges of the wheel (10 5 light years in diameter) Intruder galaxy is no longer visible This is from HST

Active Galaxies Quasars Quasi-stellar radio source. (A radio source that is so far away that it looks like a star.) Bright nucleus Highly variable Most produce strong X-rays Seyfert galaxies Spiral galaxies with bright nucleus Seyfert 2 galaxies are viewed through gas disk

Active Galaxies Radio galaxies quasars with radio emission (original quasars) some have two lobes, connected by jets some are wildly variable and have X-rays not especially bright in visible light often giant elliptical galaxies Blazars wildly variable, have lots of X-rays and gamma- rays

Unified Model of AGN All AGN are the same: central BH plus disk and jets Differences in lines, jets, & spectra are due to different viewing angles Also possible that BHs are being fed at different rates

Centaurus A/Optical Giant elliptical galaxy 10 million light years away Dark dust lane obscures the central region

Centaurus A/Radio Double Lobe Radio Galaxy Image shows radio lobes superposed on optical image Central black hole must be producing radio jets and lobes

Centaurus A/X-ray X-ray image from Chandra Bright nucleus can be seen in center at location of black hole Small jet to lower right ends in shocked region

Centaurus A/IR IR map shows a second galaxy (barred spiral) hiding inside Cen A’s dust lanes Elliptical’s gravity helps barred spiral maintain its shape Material funneled along the spiral's bar fuels the central black hole which powers the elliptical's radio lobes Symbiotic relationship