Observational Constraints of of Observational Constraints of of Reionization History in the JWST EraReionization History in the JWST Era
Xiaohui FanXiaohui Fan
University 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