Observational Constraints of of Observational Constraints of of Reionization History in the JWST EraReionization History in the JWST Era

Xiaohui FanXiaohui FanUniversity of ArizonaUniversity of Arizona

Background: 46,420 Quasars from the SDSS Data Release Three

Astrophysics in the Next DecadeSep 26, 2007

From Avi Loeb

reionization

Two Key Constraints:1. WMAP 3-yr: zreion=10+/-32. IGM transmission: zreion > 6

Outline• Current Observational Constraints• Probing reionization history in the next decade

– Finding high-z sources– Observational tests for the neutral era

• Two critical tasks related to JWST– Wide-field IR surveys for z>8 quasars– Comprehensive Ly galaxy surveys at z~10

• Will not talk about:– 21cm probe– Future CMB polarization measurements– IR background and first stars

Open Questions:• When did it happen: fHI vs. z

– z~6: late– z~15: early– Extended or phase transition?

• How did reionization proceed:

– Homogeneous or large scatter? (fHI) vs. z– Topology of overlap; fHI vs.

• What did it: (gal, qso) vs. z– AGN?– Star formation?– Decay particles?

• Observational goals– Map the evolution and spatial distribution of ionization state– Find highest redshift galaxies and quasars: source of reionization

WMAP: early reionization?

• WMAP third year: = 0.09+/- 0.03– Larger signal comparing to

late reionization model (but marginally consistent!)

• However, no direct conflict to Gunn-Peterson result, which is sensitive only to ~1% neutral IGM

• Overlapping could still be at z~6

• IGM could have complex reionization history

direct observation of high-z sources

Page et al., Spergel et al. 2006

zreion = 6

Gunn-Peterson Test

• Classic G-P (1965) effect:

– Saturates at low neutral fraction• G-P damping wing (Miralda-Escude 1998)

– Sensitive to neutral IGM– Attenuates off-resonance transmissions

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GP ~105(nHI /nH )

Damping wing

Evolution of Lyman Absorptions at z=5-6

z = 0.15

Accelerated Evolution at z>5.7• Optical depth evolution

accelerated– z<5.7: ~ (1+z)4.5

– z>5.7: ~ (1+z)>11

– End of reionization?

• Evolution of neutral fraction

– fHI > 10-3 - 10-2 at z=6– Order of magnitude

increase from z~5– G-P absorption saturates;

needs more sensitive tests

(1+z)4.5

(1+z)11

XF et al. 2006

Beyond Gunn-Peterson Optical Depth:HII Region Sizes and Dark Gap

Distributions

• Size of HII region Rs ~ (LQ tQ / fHI )1/3

• Best estimate: fHI ~ a few percent at z~6

• Can be applied to higher z and fHI with lower S/N data

Shapiro, Haiman, Mesinger, Wyithe, Loeb,Bolton, Haehnelt, Maselli et al.

• Dark gap statistics – Sensitive to the topology of reionization

• z~6 observations:– Dramatic increase in gap length:

• Consistent with overlap at z~6-8– Existence of transmission at z>6 places an upper limit of average neutral fraction <30% (Gallerani et al. 2007)

Gallerani et al.

zem

Iye et al. 2006Kashikawa et al. 2006Ota et al. 2007

Ly Galaxy LF at z>6

• Neutral IGM has extended GP damping wing attenuates Ly emission line• New Subaru results

– Declining density at z~6-7 (2-3 result)– Reionization not completed by z~6.5– fHI ~ 0.3 - 0.6 at z~7– Overlapping at z=6-7?– cf. Malhotra & Rhoads, Hu et al.: lack of evolution in Ly galaxy density

GRBs as Probes of Reionization

• Detected to z=6.30• Advantages:

– Bright– Small surrounding HII

regions: could use damping wing of Gunn-Peterson trough to probe high neutral fraction

• Constraining neutral fraction– How to distinguish internal absorption

from IGM damping wing??– Using 050904: fHI < 0.6 (2-sigma) by

fitting both DLA and IGM profiles

Damping wing? GRB050904

Kawai et al. 2005

What Ionized the Universe? AGNs or Galaxies

SFR of galaxies Density of quasars

• Depends on:– Luminosity density:

• Detailed LF and IMF– Escape fraction of ionizing

photons to the IGM:• Quasar: fesc~1• Galaxies??

– Clumpiness of the IGM• Can quasars do it? Not likely

– Too few quasars unless QLF remains to be steep to AGN luminosity

– Extra constraints from X-ray background

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˙ N ion ∝ ρ 912ΑL fescCIGM

Reionization Budget

Reionization by stellar sources?Reionization by stellar sources?

Necessary for reionization 6<z<9 (Stiavelli et al 2003)

• Large uncertainties in reionization photon budget:– IGM clumpiness; IMF; escape efficiency– Large cosmic (sample) variance in deep field data– Galaxy luminosity function at high-z

• Sources of reionization have not been identified!– Most likely dwarf galaxies

Bouwens & Illingworth;Bunker et al. ; GnedinYan and Windhorst

Probing Reionization History

Fan, Carilli & Keating 2006

Quest to the Highest Redshift

Next Generation Quasar Surveys

• Optical surveys: limited to z<7• New generations of red-sensitive CCD devices

– Improved QE at 1 micron (Y band)– SUBARU/Princeton (2010+): a few hundred deg, Y<25;?– Pan-Starrs (2008+): 3: Y<22.5; 1000 deg2: Y<24; 30 deg2: Y<26– LSST (2013+): 3: Y< 25– Discovery of large number of quasars at z<7.5

• New generation of Near-IR surveys:– UKIDSS (2005 - 2012?): 4000 deg2: JAB<21

– VISTA/VHS (2008+): 20000 deg2: JAB<21

– VISTA/VIKING (2008+): 1500 deg2: JAB<22

– VISTA/VIDEO (2008+): 15 deg2: JAB<24.5– Discovery of a handful of quasars at z=7-9

Probing the Neutral Era with JWST Quasar Spectroscopy

• Measuring G-P optical depth– R~100 mode for faint AGNs– Insensitive to neutral era

• Measuring HII region sizes– R~1000 mode– Sensitive to high fHI

– Radiative transfer effects causing large scatter for individual object

– Modest S/N but require large sample – JAB<24.5 (deep surveys)

JWST/NIRspec300k sec

• Probing reionization using dark gap distribution:– R~2700 mode– Sensitive to overlap

topology– JAB<22.5 (wide surveys!)

Evolution of IGM Metals• Early Enrichment of the

IGM by First stars– Lack of evolution in metal

line density up to z~6• OI Forest (Oh 2002)

– OI and H have almost identical ionization potentials

– In charge exchange equilibrium with H but much lower abundance

– Fluctuating OI forest during neutral era to probe ionization topology and metal pollution in the IGM

OI system at z=6.26

Becker et al. 2006

Ryan-Weber et al.

Evolution of CIV systems

Will there be enough quasars?

• For z>9 (assuming quasar LF evolution has not steepened)– Bright (AB<22.5): 0.2/100

deg2

– Faint (AB<24.5): 1-10/100 deg2

• difficult for current or planned ground-based IR surveys to find enough quasars for JWST reionization probes…

Number expected Based on z~6 QLF

Spitzer Warm Mission Survey?

• Wide-field IRAC survey as path-finder to JWST (Gardner, XF, Wilson, Stiavelli)– 500 deg2 to SWIRE depth– Combined with deep optical/near-IR data for selection

4yr

½yr eROSITA

e-ROSITA• All sky X-ray survey

– PI. G. Hasinger– Launch 2011– Expect:

• 60 quasars at z>7• 20 at z>8• 5 at z>9

Lyman Emitter at z~10?

• Keck blind spectroscopic survey along critical lines of high-z clusters– Six promising Ly emitter candidates

at z=8.7 - 10.2– Large abundance of low-L galaxies;

providing sufficient reionization photons

– Limit of ground-based search; extremely difficult to confirm spectroscopically Stark, Ellis et al.

Ground-based Ly surveys• DAZEL - The Dark Age

Z(redshift) Lyman- Explorer on VLT: – dedicated Ly narrow band

survey instrument for z=7 - 10– ~ 1 object per 10 hour field

• New generation of OH suppression technique and AO:– Ground-based surveys could

find Ly emitters at z<12

McMahon et al.

J H K Bland-Hawthorn

Reionization Topology with Ly Emitters• Ly emitter could provide sensitive probe to

reionization history, especially during overlapping– Evolution of LF (constrain fHI)– Clustering– genus numbers

Distribution of Ly emittersover JWST FOV

McQuinn et al.Angular correlation of Ly emitters Neutral Ionized

Ly Emitter Surveys in JWST Era

• Interpretation of Ly emitters alone is highly model dependent:– Evolution of continuum

LF– Uncertainties in Ly

radiative transfer– Intrinsic clustering of

galaxies etc.• Requires surveys of

continuum and SF selected samples

intrinsic observed

Ly selected continuum selected

Rhoads 2007

Synergetic survey of galaxies in reionization era

NIRSpec FGS/TFI

Synergetic Survey of Galaxies in Reionization

Era • JWST will detect sources that

reionization the Universe at z>10– Ability to find high-z sources

limited by whether the Universe managed to make them

• Ground-based and JWST/TFI will detect Ly and HeII emitters to probe reionization history and topology

• ALMA will provide dust/star-formation/dynamics

Windhorst et al.

Wish List to Theorists• Reionization Simulation

– Volume: hundreds of Mpc– Resolution: dwarf galaxy

halos and Lyman Limit Systems

– Radiative transfer– Star formation prescriptions– Contribution from Pop III

• Ly emission physics • Understanding escape

fraction of ionization photons

Gnedin and Fan 2006

Escape Fraction: A Key Uncertainty

• Escape fraction (as a function of z, L, age) affects:– Total reionization budget– HII region sizes– Ly emitter probe

• Current measurements extremely uncertain– Shapley et al. at z~3: 2/14 detections– Siana et al. at z~1: fesc <0.02;

evolution?– Large HST surveys underway

• But how to measure it at z>6???

Siana et al. 2007

Summary• What do we know now about reionization?

– zrei = 6 - 13– Overlapping probably late with extended reionization process– AGN not likely sources of reionization; situation for galaxies uncertain

• What do we expect to know before JWST– Reionization history to z~8 from quasars/GRBs

• Needs more powerful quasar surveys (Spitzer warm and eROSITA)– Small number of Ly emitters at z=7 - 10– Lyman break-selected population at z~8-10 from WFC3: better constraints

on reionization budget– Progress in reionization simulations

• Roles of JWST– Absorption line probes using high-z quasars– Identify the reionization population– Mapping out Ly emitters at the peak of reionization, synergy with ALMA

and GSMT/ELT

Probing Reionization History

JWST, GSMT21cm, GRB, ALMA

Fan, Carilli, Keating 2006