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Galaxy Formation

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

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Galaxy Formation

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  1. Galaxy Formation • Formation of galaxies in cold dark matter universe

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

  3. 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

  4. 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

  5. Edge-on Spiral Galaxy • NGC 891 - we think our Galaxy looks like this This is an infrared composite image from KPNO

  6. Spiral sequence • Hubble Space Telescope • Sandage NGC 7537/Sbc

  7. NGC 1232/VLT NGC 1288 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.

  8. Spiral sequence • Hubble Space Telescope • Sandage NGC 5838/S0

  9. Spiral sequence • Hubble Space Telescope • Sandage NGC 5689/Sa

  10. 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

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

  12. 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

  13. 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

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

  15. 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.

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

  17. Galaxy Collision

  18. Galaxy Collisions, Part 2

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

  20. Center of M31 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 Mo

  21. Cartwheel Galaxy • Wheel shape was formed from collision of two galaxies • Bright stars are forming at the edges of the wheel (105 light years in diameter) • Intruder galaxy is no longer visible This is from HST

  22. 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

  23. 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

  24. 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

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

  26. 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

  27. 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

  28. Symbiotic relationship 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

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