Cosmological ReionizationCosmological Reionization

Nick Gnedin

OutlineOutline

•The brief history of time•What we know about reionization•Reionization: ABC•Data vs theory•Conclusions

The Brief History of TimeThe Brief History of Time

Today:z=0

t=13.7 Gyr

End of inflation:z=1027

t=10-36s

Recombination:z=1089

t=379 kyrionized neutral ionized

RE-IONIZATIONRE-IONIZATION

What We Know About What We Know About ReionizationReionization

Ly- Ly-

What We Know About What We Know About Reionization: A or B?Reionization: A or B?

Sloanquasars

Frac

tion

of fl

uxtr

ansm

itted

“…the universe is approaching the reionization epoch at z~6”

(Becker et al. 2001)

SimulationsSimulations

• 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 Cosmological Parameters 20032003

Baryons: 4%Dark matter: 23%Dark energy: 73%

…

How It All Happens… How It All Happens…

GalaxiesHII regions

Neutral hydrogen

4 chimps

How It All Happens… How It All Happens…

How It All Happens: ABCHow It All Happens: ABCPre-overlap: HII regions

expand in the low density gas.

Overlap: HII regions merge – the moment of reionization.

Post-overlap: High density regions are being ionized from the outsize.

Redshift of OverlapRedshift of OverlapPre-overlap

Overlap Post-overlap“A redshift of reionization”

Redshift of OverlapRedshift of Overlap

zREI = 6.1 + 0.3 (2)

WMAP modelWMAP 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 quasarsSLOAN quasars

Lyman-Break Galaxies Lyman-Break Galaxies Observed LB galaxies Simulated galaxies

L

Obs

erva

tions

Sim

ulat

ions

Dwarf GalaxiesDwarf Galaxies

Real dwarfs

Virtual dwarfs

Star FormationStar Formation

MetallicityMetallicity

KinematicsKinematics

But But

= 0.17 = 0.06 = 0.17

Conclusions IConclusions I• Reionization proceeds in 3 stages:• In the pre-overlap stage more-or-less isolated HII regions expand into the neutral IGM (bubbles of ionized gas in the sea of neutral gas). Measurement of high indicates that new physics was present in this stage. • During the overlap isolated HII regions merge together (looks like a mess). It happened at zREI = 6.1 + 0.3.

• 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 IIConclusions II

• Our theoretical models reach the stage when we are able to make a quantitative comparison between theory and all existing observational data.• Future observations will be matched by the adequate progress in our abilities to model formation of early galaxies and supermassive black holes.• If this decade is a decade of CMB in astronomy, the next one will be a decade of reionization.

The EndThe End

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