6 - 10 - 176 - 10 - 17

Nick Gnedin

(Once More About Reionization)(Once More About Reionization)

Co-starringCo-starring

OutlineOutline

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

All You Need to Know About All You Need to Know About the Lyman-alpha Forestthe Lyman-alpha Forest

Lyman-alpha emission line

Intrinsic QSO spectrum

Absorbed flux Transmitted flux

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 ReionizationRedshift of ReionizationPre-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 ReionizationRedshift of Reionization

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

Dwarf GalaxiesDwarf Galaxies

Local Group dwarfs

Dark matter halos

Dwarf Galaxies IIDwarf Galaxies II

Real Local Group dwarfs Virtual dwarfs

$2,000

Quiz: how much is one blue square?

But… But… (as of Feb 2003)(as of Feb 2003)

= 0.17 = 0.06 = 0.17

But…But…(as of Oct 2003)(as of Oct 2003)

=17+4%

=12+6%

=10+6%

Polarization

TemperatureGalaxy clustering

Important ConclusionImportant Conclusion

Spectra of SLOAN quasars are unambigious:

zREI = 6.2 + 0.3

WMAP result suggests:

Ionization history may be non-trivial

Lyman-Lyman- Absorption Absorption

• Post-overlap stage: the most powerful method to probe the ionization state of the IGM.

• Pre-overlap: only useful for studying very large HII regions around very rare quasars.

We need to use a different band of the EM spectrum to study the pre-overlap

stage!

Why Radio?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) cm21(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 Why You Shouldn’t Watch TV (and listen to radio too)(and listen to radio too)

130 MHz

z=10

160 MHz

z=8

200 MHz

z=6.2

108 MHz

z=12

Nothing can be observed at z>12

FM Radio band Broadcast TV bands

Observing Reionization:Observing Reionization:Angular FluctuationsAngular Fluctuations

1o degree

• Large-scale density fluctuations

• Individual HII regions from high-z quasars

Sources of fluctuations:

Radio point sources killthem all

Observing Reionization:Observing Reionization:Frequency FluctuationsFrequency Fluctuations

Foregrounds

Mean signal

Observational error in 10 days

Is It For Real?Is It For Real?

1

5

25

Radio ForestRadio Forestz~4 z~10

Ly-

21cm

Radio Forest IIRadio Forest II

Strong absorption lines

Radio Gunn-Peterson trough

Are There Sources at High Are There Sources at High Redshift?Redshift?

Sour

ces

on th

e sk

y

10

102

103

104

7 8 10 11 129 13

RedshiftExtrapolation of QSO evolution

Constant comoving density

Truth is somewhere here(pre-WMAP)

Truth is somewhere here(post-WMAP)

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).• During the overlap isolated HII regions merge together (looks like a mess). It happened at zREI = 6.2 + 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

• 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 IIIConclusions III

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

The EndThe End

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