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The Birth of Galaxies
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  1. Rob Simcoe March 8, 2007 The Birth of Galaxies

  2. Distribution of Matter in the Local Universe: 385,600±4000 Years after the Big Bang Million atoms per m3

  3. Distribution of Matter in the Local Universe: 13.7 Billion Years Later (i.e. Today) Milky Way Intergalactic gas r~ 1atom per 6.5 m3 ~1 atom / cm3 Andromeda (M31) M33 Stars: ~1026 atoms/cm3

  4. How did all the matter end up in small volumes? Structure formation movie Collapse of cosmic structure from gravitational runaway

  5. First Stars Star Formation Peaks 5 10 Gyr 1 Big Bang t=0 Today: t=13.7 Gyr z 5 4 3 2 1 Galaxy Assembly “Coasting” Turn Back the Clock:Out in Space = Back in Time First microbial life? Dinosaurs extinct (13.63 Gyr) Earth Forms (9.2 Gyr)

  6. Early Epochs are Studied Using Highly “Redshifted” Objects • Big Bang • Cosmic expansion • Deeper meaning: size scale of expanding universe Observed Flux

  7. Early Epochs are Studied Using Highly “Redshifted” Objects • Template matching • See object as it was when light was emitted • Similar objects have similar spectra • Differences interesting! • Evolving populations • Intervening matter Redshift is the fundamental tool we use to identify sources from the early universe

  8. A useful way to visualize the (real!) universe Credit: SDSS, WMAP, COSMUS

  9. How far can we see? z ~ 0.5: Wide-field galaxy surveys z ~ 1100: Cosmic Microwave Background (photon limit) z ~ 3: quasars, deep galaxy spectra z ~ 6: ultra deep fields, most distant observable objects ??

  10. Two “Standard” Approaches for Observing Early Galaxy Formation • Direct • Find & study actual galaxies • Indirect • Look at effects the objects have on their surroundings

  11. Method 1. Brute Force: Add up Starlight

  12. Neutral Hydrogen Atoms Interact with Light EMIT light at radio wavelengths ABSORB light at Ultraviolet wavelengths l = 122 nm p+ e- Both processes involve an electron-proton pair Neither works if electron removed! l= 21 cm n = 1420 MHz

  13. 7.9 7.6 8.3 8.5 z = 12 10.5 10 11 9 The First Stars Strip Electronsfrom Intergalactic Gas = Ionized (electron removed) = Neutral (electron attached) Redshift Time

  14. Ionized Neutral Method 2. Indirect Effect of Stars:Neutrality of Intergalactic Gas • Quasar spectra • >1000x brighter than gals • Handful known at z>6 • Flux completely absorbed at z ~ 6 • Stars were shining <1 Byr after Big Bang • Dynamic range issues hydrogen

  15. Large Modern Telescopes Observe Distant, Faint Sources

  16. Data Template Observational Power of Magellan

  17. Early Universe was Filled with Heavy Elements! • Quasar spectra: core samples of intergalactic matter Signature of carbon atoms

  18. Mileura Widefield Array: MWA First Photons! Mileura Station, Australia

  19. Next Generation Telescopes: Optical/IR James Webb Space Telescope: NASA 20-30 meter ground-based telescopes Giant Magellan Telescope MIT: Schechter Decadal survey priorities

  20. Future Facilities: Radio

  21. Toward “First Light” z ~ 6: most distant observable objects (2007) Redshift 6 – 15: The First Gyr JWST Giant Telescopes 21 cm (MWA/SKA)