Probing Reionizationwith z>6 Quasars

Richard L. WhiteSpace Telescope Science Institute

STScI Workshop, 2006 March 13

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CollaboratorsRick White (STScI)

Bob Becker (UCD/LLNL)Xiaohui Fan (Arizona)Michael Strauss (Princeton)

… and the Sloan Digital Sky Survey Consortium

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Quasar composite spectraV

anden B

erk et al. 2001, A

J, 122, 54

9

Rest Wavelength (Å)

Flu

x D

ensi

ty f

(A

rbit

rary

Uni

ts)

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Quasar colors in SDSS filtersR

ichards et al. 2001, A

J, 121, 230

8

Blue Red

Re

dB

lue

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Quasar colors vs. redshiftR

ichards et al. 2001, A

J, 121, 230

8

Re

dB

lue

u -

g

g -

r

r -

i

i - z

The Lyman forest

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Selecting high-z quasars with

SDSS + infrared

Fan et al., 2003, AJ, 125, 1649

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Echelle Spectrograph & Imager Keck ESI raw spectrum

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19 quasars

with z>5.7

Fan et al., astro-ph/0512082

And they’re still coming…• 5 new z > 6

quasars found at Keck since January 2006

• Including the first z>6 quasar found without SDSS:a FIRST radio-selected quasar at z=6.1

~

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SDSS J1030+0524 z=6.31

White et al., 2003, AJ, 126, 1

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SDSS J1148+5251 z=6.42

White et al., 2003, AJ, 126, 1

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Gunn-Peterson troughs at z=6W

hite et al., 2

003, AJ, 126, 1

15

(Ly ) vs. redshiftF

an et al., astro-ph/0512082

16

(Ly ) vs. redshiftF

an et al., astro-ph/0512082

17

Evolution in photoionization rateF

an et al., astro-ph/0512082

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Line profiles at blue edge of Lyman emission

Fan et al., astro-ph/051208

2

z>6.1z=5.9–6.1z=5.7–5.9

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H II region sizes around quasars

• Size of ionized Strömgren sphere:

– Increases with number of ionizing photons emitted in quasar’s lifetime

– Decreases if IGM becomes more neutral– Decreases at higher redshift

• Assumes recombinations are not important rec ~ 5x107 yrs at z=6.4

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Observed H II region sizes around quasars

Fan et al., astro-ph/051208

2

• Conclusion:– Sizes decrease by

factor of 2.7 from z = 5.7 to 6.4t = 1.4x108 yrs

– Implies neutral fraction increases by factor of 14

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Summary of neutral hydrogen constraints from quasar spectra

Fan et al., astro-ph/051208

2

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Summary

• Quasars are the most easily studied probes of the intergalactic medium at z > 6– But only one bright z > 6 quasar per 500 square degrees

• z = 6 probably marked the end of reionization– Neutral fraction still fairly low, fHI ~ 0.03 at z = 6.4

• Strongest limits:– Absorption in Ly and Ly Gunn-Peterson troughs

– H II region sizes in proximity zone measured fromLy line profiles