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From Darkness, Light: Computing Cosmological Reionization


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Talk by Prof. Romeel Dave' at the SuperJEDI conference, July 2013

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From Darkness, Light: Computing Cosmological Reionization

  1. 1. From Darkness, Light:From Darkness, Light: Computing Cosmological ReionizationComputing Cosmological Reionization Romeel Davé With: Kristian Finlator, Feryal Özel, Ben Oppenheimer Movie by T. di Matteo
  2. 2. HI
  3. 3. James Webb Space Telescope “First Light Machine” Planck: CMB at high precision Atacama Large Millimeter Array Square Kilometer Array Reionization: A Multiwavelength Approach
  4. 4. When did reionization occur (start and end)? What are the sources that reionized the Universe? How did reionization transpire in space and time? Fundamental Questions of Reionization
  5. 5. Observational Constraints: HI Optical Depth Bolton & Haehnelt (2007) Quasar spectra show sudden rise in τHI at z~6. SDSS
  6. 6. Observational Constraints: CMB Polarization CMB T-E cross-correlation @ low-l shows enhanced signal from free electrons. zreion~10±1
  7. 7. Observational constraints: z>6 galaxies Bouwens et al. (2008) z=4 z=5 z=6 z=7 z=6.96: Iye et al (2008) Hundreds of (putative) z>6 galaxies now seen. No unambiguous signature of reionization. JWST
  8. 8. - Reionization began at z>~10 (0.5 Gyr) - Reionization ended at z~6 (1 Gyr) - There are plenty of galaxies (and very few quasars) seen at z>~6. Do galaxies alone emit enough photons to reionize? Observations tell us…
  9. 9. QI = Volume-averaged filling factor of ionized gas nph = # of ionizing photons per unit volume trec = recombination time Clumping factor CHII = <nHII ne>/<nHII><ne> Can (in principle) measure dnph/dt. But to solve reionization, need CHII , i.e. topology. Analytic Reionization z=9, 1 Mpc/h, dark matter
  10. 10. Outside-in: Voids reionize first, then dense regions Inside-out: Regions around galaxies ionize first, then voids Competition between: - Sources forming in overdense regions - Galaxies are highly clustered at early epochs vs. - High recombination rates in dense regions - Dense regions more self-shielded (shadowing) Analytic results highly assumption-dependent. Simulate! Topology of Reionization
  11. 11. Simulating Reionization: Physics (1) structure formation with gas (density, temperature evolution) (2) sources of photons (normal stars, Pop III stars, AGN, exotica) (3) non-equilibrium thermal state (4) non-equilibrium ionization state (5) radiation transport
  12. 12. 1 2 3
  13. 13. Code Comparison Code method c=? shadows scaling comments C2-ray ray-tracing ∞ yes N* Nx 3 n-body ART ray-tracing ∞ ? N* Nx 3 FLASH-HC ray-tracing ∞ yes N* Nx 3 TRAPHIC ray-tracing c yes Nc NSPH mass resolution limit? CRASH Monte carlo ∞ yes N* Nγ time dependence? OTVET* moments << c ? Nx 3 optically-thin fEdd MARCH* moments c yes Nx ~4 accurate fEdd ; highly flexible; use SPH sim's Zel'dovich approximation +irradiated boundary * Have been implemented into a cosmological radiation-hydro code
  14. 14. The Moments of the Transfer Equation - Derive fEdd from accurate long-characteristics → minimize artifacts; enhance shadowing See also Auer & Mihalas (1970); Stone, Mihalas, & Norman (1992) Eddington tensor
  15. 15. The Future: HI 21cm maps Redshifted 21cm (~100 MHz) traces HI directly. dTbright~xHI(Tspin-TCMB) In principle, map HI distribution and get clumping factor. Kinetically coupled to gas Ts~(1+z)2 Returns to CMB Ts~(1+z)Santos+10
  16. 16. Summary Reionization is a frontier for both observations and theory - Planck, JWST, LOFAR, SKA, … all will play major roles - Simulations will require next-gen techniques + technology Our new fast & accurate cosmological rad-hydro code… - Makes no physical approximations (outside of galaxies) - Moment-based; doesn’t scale with # of sources - Still limited by dynamic range Interesting early results: - Galaxies with normal star formation can reionize - But… hard to match all current constraints with normal SF - Topology of reionization: inside-outside-middle - Clumping factor decreases rapidly with time; ~2-3 by z~6