Nick Gnedin (Once More About Reionization)

Co-starring Gayler Harford Katharina Kohler Peter Shaver Mike Shull Massimo Ricotti

Outline 6! (Are we there yet?) 17? (Graduate students, cheer up!) 10?! (Why you shouldn’t watch TV.) Conclusions

The Brief History of Time Today: z=0 t=13.7 Gyr End of inflation: z=10 27 t= s Recombination: z=1089 t=379 kyr ionized neutralionized RE-IONIZATION

All You Need to Know About the Lyman-alpha Forest Lyman-alpha emission line Intrinsic QSO spectrum Absorbed fluxTransmitted flux

What We Know About Reionization Ly-  Ly- 

What We Know About Reionization: A or B? Sloan quasars Fraction of flux transmitted “…the universe is approaching the reionization epoch at z~6” (Becker et al. 2001)

Simulations dark matter dynamics gas dynamics star formation metal cooling exact physics of primeval plasma fine print (secondary electrons, Ly-  pumping, …) radiative transfer That’s the key!  the only phenomenology! Note: non-existing things are not included

Cosmological Parameters 2003 Baryons: 4% Dark matter:23% Dark energy:73% … WMAP

Star Formation Schmidt Law: Parameters: star formation efficiency  SF UV emission efficiency  UV ( =E UV /M * c 2 )

How It All Happens… Galaxies HII regions Neutral hydrogen 4 chimps

How It All Happens…

How It All Happens: ABC Pre-overlap: H II regions expand in the low density gas. Overlap: H II regions merge – the moment of reionization. Post-overlap: High density regions are being ionized from the outsize.

Redshift of Reionization Pre-overlap Overlap Post-overlap “A redshift of reionization” Reinstate (v.t.): to restore to a former state. Reionization (noun): moment in the history of the universe when last 1(0.1)% by mass (volume) of neutral hydrogen disappears in the low density IGM. Reiterate (v.t.):

Redshift of Reionization z REI = (2  )

WMAP model Individual spectra of bright quasars are very similar to that of SLOAN quasars. Large galaxies at z~4 have colors identical to observed Lyman Break Galaxies. Star formation rate is consistent with observational measurements at z~4. Smallest galaxies formed in the simulation look like dwarf spheroidals in all their properties, including abundance (no satellite problem). Lyman-alpha forest (including metal absorption systems) is consistent with observations. but …

SLOAN quasars

Lyman-Break Galaxies Observed LB galaxies Simulated galaxies

Dwarf Galaxies Local Group dwarfs Dark matter halos

Dwarf Galaxies II Real Local Group dwarfs Virtual dwarfs $2,000 Quiz: how much is one blue square?

But… (as of Feb 2003)  = 0.17  = 0.06  = 0.17

But… (as of Oct 2003)  =17+4%  =12+6%  =10+6%  Polarization Temperature Galaxy clustering

Important Conclusion Spectra of SLOAN quasars are unambigious: z REI = WMAP result suggests: Ionization history may be non-trivial

Lyman-  Absorption Post-overlap stage: the most powerful method to probe the ionization state of the IGM. Pre-overlap: only useful for studying very large H II regions around very rare quasars. We need to use a different band of the EM spectrum to study the pre-overlap stage!

Why Radio? We need to study hydrogen. All hydrogen is in the ground state. There are only two observable transitions from the ground state of atomic hydrogen: Lyman-  21 cm Lyman-  is not good (it is an allowed transition). So…

21(1+z) cm 21 cm   1420 MHz Redshift to 6.2   200 MHz Redshift to 8   160 MHz Redshift to 10   130 MHz

Why You Shouldn’t Watch TV (and listen to radio too) 130 MHz z= MHz z=8 200 MHz z= MHz z=12 Nothing can be observed at z>12 FM Radio band Broadcast TV bands

Observing Reionization: Angular Fluctuations 1 o degree Large-scale density fluctuations Individual H II regions from high- z quasars Sources of fluctuations: Radio point sources kill them all

Observing Reionization: Frequency Fluctuations Foregrounds Mean signal Observational error in 10 days

Is It For Real? 11 55 25 

Cosmic Equation of State Cosmological constant  : p = -  Something very exotic: p = f(  ) z=0z~10 growth rate  equation of state  LOFAR

30%10%3% Cosmic Equation of State II Let’s assume: p = (-1 + w 0 + w 1  /  0 )  (linear and quadratic terms). Measure growth rate to:

Radio Forest z~4z~10 Ly-  21cm

Radio Forest II Strong absorption lines Radio Gunn-Peterson trough

Are There Sources at High Redshift? Sources on the sky Redshift Extrapolation of QSO evolution Constant comoving density Truth is somewhere here (pre-WMAP) Truth is somewhere here (post-WMAP)

Conclusions I Reionization proceeds in 3 stages: In the pre-overlap stage more-or-less isolated H II regions expand into the neutral IGM (bubbles of ionized gas in the sea of neutral gas). During the overlap isolated HII regions merge together (looks like a mess). It happened at z REI = In the post-overlap stage the remains of the neutral gas are being ionized from the outside – most of them become Lyman-limit systems (bubbles of neutral gas in the sea of ionized gas).

Conclusions II First detection of 21 cm emission from pre-reionization era should be attempted in frequency domain within the single beam. These observations will allow to probe the global reionization history and large scale perturbations (including high- z quasars). Observations of radio absorption lines will compliment emission studies by probing small scales.

Conclusions III A professional duty of every astronomer is to stop listening to FM radio and watching broadcast TV until such a measurement is completed.

Imagine If You Were a Hydrogen Atom…

The End

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