Post GP-WMAP Reionization: the morning after

We need quantitative measures of

•Epoch of reionization (Zreion)

•Neutral fractions

•Volume fraction of ionized/neutral gas

• duration of reionization (Zreion)

•Sizes of bubbles: topology

Measuring reionization with Lyman- emitters

Lyman- galaxy test: neutral fractions, volume fractionslocalscaleable

relevant at neutral fractions of <f(HI)>~0.1-0.5Can be done with today’s technology (some progress already made)

Complements GP, WMAP and 21 cm.

The Lyman- ReionizationTest

To

Observer

Ionized IGM

Young starburst

Lyman- photons

Continuum Photons

(Damping wing is a feature, not a bug)

The Lyman- Test

To

Observer

Neutral IGM

Young starburst

Lyman- photons

Continuum Photons

(Miralda-Escude 1998; Miralda-Escude & Rees 1998;

Haiman & Spaans 1999; Loeb & Rybicki 1999)

To

Observer

Neutral IGM

Young starburst

Lyman- photons

Continuum Photons H II

region

(Madau & Rees 1999; Rhoads & Malhotra 2001;

Haiman 2002)

The Lyman- Test, First Order Concerns: HII Regions

historyLy- lines were expected to be invisible in a neutral IGM until Hu

et al. 2002 found a source at z=6.6.

Then everyone rushed to explain why we could see Ly- even in a neutral IGM: ionized bubbles, winds …

But hard to avoid attenuation of factors of 2-3 (Santos 2004)

How do you know that any individual object was not intrinsically brighter?

Statistical test on the population

Lyman- Luminosity Functions• Luminosity function fits on all

available data at z=5.7 and 6.5– Santos et al. 2004, Taniguchi et al.

2004, Rhoads et al. 2004, Kurk et al. 2004, Tran et al. 2004, Hu et al. 2002, Hu et al. 2004, Ajiki et al. 2004, Rhoads et al. 2003, Rhoads & Malhotra 2001 (few tens of nights on large telescopes)

• z = 6.5 plot shows two hypotheses:

– z = 5.7 LF, or– z = 5.7 LF reduced by a factor

of 3 in luminosity to approximate IGM absorption.

• No evidence for neutral IGM!

Charting ReionizationThere is no contradiction between the GP effect at z=6.2 and

the Ly test at z=6.5; remarkable agreement with the dark gap tests (Fan et al. 2005)

1st order concern 1.Cosmic variance in samples

Monte Carlo simulations to account for cosmic variance: All observed densities allowed to vary by factor of 2.– Circles: z = 5.7

– Triangles: z = 6.5

– Squares: z = 5.7 with L* divided by 3.

1st order concern 2.Picket fence effect

Suppose you obliterate some fraction of the sources completely, and the other half remains untouched in luminosity.

Then phi* should decrease

- it is seen to increase slightly at z=6.5 compared to z=5.7

Concern 3: redshift evolution:

none seen so far! LALA Lum Fn at z=4.5

(Dawson et al. 2005)

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

LALA Lum fn at z=4.5

4. Bright end of luminosity function

• See Haiman & Cen 2005, for luminosity dependent attenuation: the conclusions do not change significantly.– Higher luminosity objects

possibly create larger ionized bubbles around themselves.

• Furlanetto et al. 2005, conclude that neutral fraction is 50% compared to ~30% as in MR04.

Stromgren spheres:

• Rss= 0.7 Mpc/(1+z) {L43t8 (fesc/(1-fesc))}1/3

L* = 42.5

Age < 10 8 years

Best estimate of Rss < 0.7x0.3 Mpc

= 1.2 Mpc / Rss ~ 5 : optical depth at the line center

Concern 5: Clustering around Ly-a sources

1. What about clustering and Stromgren spheres created by unseen sources around Lyman-alpha emitters at z=6.5?

• Need to boost the ionizing flux by a factor of 10: possible in simulations: Wyithe & Loeb 2004, Furlanetto et al. 2004:

• deep ACS imaging around one z=6.5 source shows no dramatic overdensity (Rhoads et al. in prep.) Stiavelli et al. 2005 see an overdensity at z=5.9 around a Sloan quasar at z=6.2

Agnostic about this possibility

The volume test:(Malhotra & Rhoads, 2006, submitted)

• We know the space density of Lyman- galaxies at z=6.5 > 1x10-4 cMpc-3 (Taniguchi et al. 2005)

• Place each one in a ionized bubble of the smallest size to enable escape of half of the line flux in an otherwise neutral medium– [V(I)] > 4/3(RssMpc)3

Suppose each Lyman- emitter is visible because of a local Stromgren sphere, created by neighboring undetected dwarf

galaxies, hidden AGNs, tooth fairies …

Getting the volume (details):

V=250 Km/s• T=50%

• Rss=1.2 pMpc=1.2x7.5 cMpc

• Number density – n > 1.2-1.8e-4 cMpc3

Improvements:

• Better luminosity functions: better constraints on T. At present T > 50%, but how much more?

• Fainter sources, higher source density.

• Velocity offsets.

• Clustering of Ly-alpha galaxies.

Shimasaku et al. 2005 at z=5.7

Extension to redshifts z > 7

• Windows in the atmospheric OH spectrum continue into the J and H bands, though narrower.

• Newest NIR cameras have A sufficient for plausible Ly- searches.

• Several efforts under way…– Horton et al 2004 (DAzLE project): VLT + DAzLE) z ~ 7.7– Smith et al (see Barton et al 2004): Gemini + NIRI, z ~ 8.2– Willis et al (“ZEN” project): VLT +ISAAC, z ~ 8.8– Cuby et al: VLT +ISAAC, z ~ 8.8

Summary

• Ly-a luminosity function test at z=6.5 implies neutral fraction x(HI)<50% at z=6.5

• Space density of observed Ly-a implies a volume fraction of ionized gas V(I) > 30%.

• Limits on V(I) can be improved by going fainter and finding more galaxies, better luminosity functions and velocity offesets between Ly-a and other lines : JWST.

• Can go to higher redshifts and track the evolution of reionization as a function of z: WFC3, JWST