Solving the Reionization Conundrum….1/23 What Constraints Can we Get on the Reionization History...

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1/23 What Constraints Can we Get on the Reionization History from the Optical/Near-Infrared? Ranga Ram Chary Planck/Spitzer/Caltech

Transcript of Solving the Reionization Conundrum….1/23 What Constraints Can we Get on the Reionization History...

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What Constraints Can we Get on the Reionization History from the

Optical/Near-Infrared?

Ranga Ram CharyPlanck/Spitzer/Caltech

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WMAP constrains large HI fractions…..weakly

WMAP 1σ range

=0.084±0.016

z<6 contributes ~0.04

So 0.044+/-0.016measures reionization history.

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End Stages of Reionization: Constrained by Sloan QSOs

•Fan et al., Becker et al., Djorgovski et al. spectra of Sloan quasars showing the Gunn-Peterson trough•Evidence for N_H~<10-3.5

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We can measure the comoving rate density of ionizing photons i.e. the SFR

Δz~3; ≤400 Myr

Δz~9; ~700 Myr

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λ<912Å photon

Need 1 photon/baryon to start reionization

Need ~3-10 photons/baryon to maintain ionized hydrogen due to recombinations

Sensitive to:1. Clumpiness of the

gas2. Temperature of the

gas3. Co-moving electron

density

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Clumping Factor of Gascan only be estimated from simulationse.g. Trac & Cen

Photon Production Rate =Hydrogen Ionization + Recombination Rate

There are some nuisance parameters

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And the Escape Fraction is poorly known

Siana et al. 2010

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Minimum Required Evolution of UV Luminosity Density for Reionization

Slow

Fast

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Some uncertainty in the faint end slope of the UVLFBut clear evolution in L* between 6 and 7

Solid lines: Required for ReionizationDashed lines: Measured

Data/fits fromBouwens et al. ‘08Bouwens et al. ‘10

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6 7 10 13 14

6 7 10 13 14 22 23 24

Fast Reionization

Slow Reionization

z Age(Gyr)

6 0.95

7 0.78

10 0.48

13 0.34

14 0.30

22 0.16

But L* has to be fixed at z>7!

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The Faint End of the Galaxy LF cannot be steeper than the Halo Mass Function

Slow reionizationEvolving L*

Slow reionizationConstant L* at z>6

Fast reionizationConstant L* at z>6

Fast reionizationEvolving L*

Dark Matter HaloMass Function

Chary & Cooray ‘10

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But to see the action, need the faint galaxies.And to see faint galaxies, need cosmic explosions

which are x1000 brighter than the galaxy.

GRB 050904z=6.295Kawai et al., Haislip et al.

J-band R-band

Can measure gas and metalsin the galaxies.

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Hint of a higher SFR at z~6 from GRB Hosts

Chary, Berger & Cowie 2007

WFC3 UDF(Bouwens)

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GRBs suggest a larger ionizing photon flux from faint galaxies

But we need at least two pieces of evidence….

The integral of the star-formation history is preserved in the stellar mass density of galaxies

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Constraints from the Spitzer Measured Stellar Mass

ObservedLabbe et al. 2010

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Astronomical Archaeology

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Population III Stars: Fluctuations in IR Background ?

Power (C_l) peaks at l~1E2-3 corresponding to degree scales

Cooray et al. ‘07, Sullivan et al.

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Spitzer image with detected sources masked

Now also being done with shallower, Akari data

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No evidence for a contribution from PopIII stars in IR Background Fluctuations

Mostly 0<z<2 dwarf galaxies which contain ~20% of the stellar mass density at these redshifts.

Chary, Cooray, Sullivan ‘08; Cooray et al 2007

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In principle, absolute CIB measurements are more insightful

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2.2 micron contributions

74%

14%

12% 0%Zodiacal LightStarsCIRBISM

140 micron contributions

37%

27% 36%

Zodiacal LightCIRBISM

Unfortunately Sky Background at Infrared Wavelengths is Dominated By Zodiacal Light

CIRB (nW m-2 sr-1)λ νIν2.2: 22.4±6.03.5: 11.0±3.3140: 25±7240: 14±3

We are literally searching for a needle in a haystack!

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COBE

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Options• Gamma-ray Bursts: Prompt spectroscopy

– luck & good IR Spectrograph on a 8-10m ‘scope

• Measuring Cosmic Infrared Background at 1/100 level from outer zody– An outer planets mission, compact, high-performance

absolute calibrated instrument (ZEBRA; PI: J. Bock; http://zebra.caltech.edu)

• Infrared Background Fluctuations– Mapping a 1-2 deg wide area and a moderately deep

survey to mask out foreground galaxies

• Deeper, larger rest-frame UV surveys e.g. JWST– 6-7 Billion $

Increasing Cost