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From Darkness, Light: Computing Cosmological Reionization Romeel Davé

Movie by T. di Matteo. From Darkness, Light: Computing Cosmological Reionization Romeel Davé With: Kristian Finlator , Ben Oppenheimer, Peng Oh, Feryal Ozel. Reionization : A Multiwavelength Campaign. Planck: CMB at high precision. Atacama Large Millimeter Array.

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From Darkness, Light: Computing Cosmological Reionization Romeel Davé

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  1. Movie by T. di Matteo From Darkness, Light: Computing Cosmological Reionization Romeel Davé With: KristianFinlator, Ben Oppenheimer, Peng Oh, FeryalOzel

  2. Reionization: A MultiwavelengthCampaign Planck: CMB at high precision Atacama Large Millimeter Array James Webb Space Telescope “First Light Machine” Extremely Large Telescope Square Kilometer Array

  3. Fundamental Questions of Reionization When did reionization occur (start and end)? What are the sources that reionized the Universe? How did reionization proceed in space and time?

  4. Observational Constraints: HI Optical Depth SDSS Fan+06

  5. Observational Constraints: CMB Polarization CMB T-E cross-correlation @ low-l shows enhanced signal from free electrons. zreion~10±1

  6. Observational constraints: z>6 Lyman break galaxies JWST z=4 z=5 z=6 z=7 Bouwens et al. (2008) Robertson et al (2010) Hundreds of (putative) z>6 galaxies now seen, a handful spectroscopically confirmed. Optimistically, can reionizeif no recombinations.

  7. Observational constraints: Lyman a emitters LAE number density shows a significant and sudden drop at z>6 relative to continuum sources: Lya is absorbed by IGM? Kashikawa+11 Dikstra+14 z=5.7 z=6.5 z=6.96: Iye et al (2008)

  8. Observational constraints: The contribution from quasars (black holes) Quasars show a rapidly dropping total emissivity, shouldn’t contribute much to reionization. BUT: Obscured quasars? Very early mini-quasars? Haardt&Madau 2012

  9. So observations tell us… - Reionization began at z>~10 (0.5 Gyr) - Reionization ended at z~6-7 (1 Gyr) - There are many galaxies (and few quasars) at z>~6. What can we learn about reionization from this? Fan+06

  10. Analytic Reionization 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. z=9, 1 Mpc/h, dark matter

  11. Topology of Reionization 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!

  12. Simulating Reionization: Physics (1) galaxy formation with gas (including cooling, SF, feedback…) (2) sources of photons (normal stars, Pop III stars, BHs?, exotica?) (3) non-equilibrium thermal state (4) non-equilibrium ionization state (5) radiation transport Must do all this concurrently!

  13. 1 2 3

  14. Code Comparison Code method c=? shadows scaling comments C2-ray ray-tracing ∞ yes N*Nx3 n-body ART ray-tracing ∞ ? N*Nx3 FLASH-HC ray-tracing ∞ yes N*Nx3 TRAPHIC ray-tracing c yes NcNSPHmass resolution limit? CRASH Monte carlo ∞ yes N*Ng time dependence? OTVET* moments << c ? Nx3 optically-thin fEdd MARCH* moments c yes Nx~4 Zel'dovich approximation +irradiated boundary accurate fEdd; highly flexible; use SPH sim's * Have been implemented into a cosmological radiation-hydro code

  15. The Moments of the Transfer Equation Eddington tensor See also Auer & Mihalas (1970); Stone, Mihalas, & Norman (1992) - Previous: Assume optically-thin f (OTVET). - Derive fEdd from accurate long-characteristics → minimize artifacts; enhance shadowing

  16. Cosmological rad-hydro: MARCH + Gadget-3 Gadget-3 includes: - Gravity, starting w/cosmological perturbations - Hydrodynamics using EC-SPH - Cooling (H,He,metal) - Star formation - Galactic outflows - Non-equilibrium ionization & thermal evol - Baryonic physics tuned using z<6 observations - Star formation provides photons; computed using population synthesis models. For now: Only normal SF (Chabrier IMF) - Assume an escape fraction from galaxies.

  17. LBG Luminosity Functions: Ionization vsWinds Without outflows, LF suppressed at low-luminosities With outflows, little suppression! In realistic model, radiative feedback is sub-dominant.

  18. Constant escape fraction? Assume fesc=0.15: Doesn’t quite work. Correct Jn @ z~6 (w/winds), but reionizeslate, and te low. Finlator+12

  19. Evolving escape fraction

  20. Clumping Factor Versus Redshift Clumping factor of ionized gas is low: CHII~5 at end of EoR. Outflows suppress CHII. Gnedin& Ostriker (1997) Bolton & Haehnelt (2008) Finlator+13

  21. A New Probe: Metal Absorbers at z>~5 HI is opaque, but not metals! Quasars now seen to z~7. Many lines, high resolution -> Constrains shape and amplitude of local flux. D’Odorico+13 Velocity

  22. OI is charge-locked to HI; only need GHI Direct prediction is pretty close, but ~2s low OI absorbing region does not fill Rvir; if it did, would strongly overproduce OI. OI doesn’t really trace IGM reionization (outside halos), unfortunately.

  23. Summary Reionization is a frontier for both observations and theory. Current observations constrain: - CMB polarization: Total optical depth to z~1100. - HI absorption: Optical depth and photon budget at z~6 - Lyman break galaxies: Number of star-forming galaxies - Lyman alpha emitters: Low-dust galaxies + IGM attenuation Interesting results: - Galaxies with normal star formation can reionize, butcurrent observations don’t see the majority of galaxies responsible. - Matching WMAP t_e and “photon-starved” reionization needs lots of early photons, e.g. a rapidly evolving fesc. - Clumping factor of ionized gas is fairly low, more like outside-in reionization. Makes reionization easier. - Metal absorbers offer a new & unique probe of reionization!

  24. 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

  25. The Topology of Reionization Inside-Outside-Middle! Filaments reionize last. http://norno.as.arizona.edu/~kfinlator/rt/index.html

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