End of Cosmic Dark Ages: Observational Probes of Reionization History

1
End of Cosmic Dark AgesObservational Probes of
Reionization History

• Xiaohui Fan
• University of Arizona
• New Views Conference, Dec 12, 2005
• Collaborators Strauss, Becker, White, Richards,
  Schneider, Gunn, Carilli et al.

2
reionization
From Avi Loeb
3
Reionzation simulation
Late, phase transition By stellar sources
Courtesy of N. Gnedin
4
Three stages
Pre-overlap
Overlap
Post-overlap
From Haiman Loeb
5
Reionization is an Interplay of

• Structure formation
• WMAP cosmology
• Star formation and feedback
• First stars
• Enrichment of IGM
• Radiative transfer
• We expect it to be a complex process

6
Open Questions

• When Early or Late
• z6 late
• z15 early
• How did reionization proceed
• Once or twice?
• Phase transition or gradual?
• Homogeneous or large scatter?
• What did it
• AGN?
• Star formation?
• Decay particles?

7
The Highest Redshift Quasars and Galaxies

• SDSS i-dropout Survey
• By spring 2005 6600 deg2 at zABlt20
• Nineteen luminous quasars at zgt5.7
• zmax6.42
• Dropout and Ly? emission galaxies
• zspec lt 6.6
• zphot 7 - 8
• GRBs
• 050904 z6.29

8
Keck/ESI 30min exposure ?
Gunn-Peterson Trough in z6.28 Quasar
Keck/ESI 10 hour exposure ?
White et al. 2003
9
(No Transcript)
10
Evolution of Lyman Absorptions at z5-6
?z 0.15
11
Accelerated Evolution at zgt5.7

• Optical depth evolution accelerated
• zlt5.7 ? (1z)4.5
• zgt5.7 ? (1z)gt11
• Dispersion of optical depth also increased
• Some line of sight have dark troughs as early as
  z5.7
• But detectable flux in 50 case at zgt6
• End of reionization is not uniform, but with
  large scatter

(1z)11
(1z)4.5
Fan et al. 2005
12
Evolution of Ionization State
UV background

• UV Ionizing background
• UV background declines by close to an order of
  magnitude from z5 to 6.2
• Increased dispersion suggests a highly
  non-uniform UV background at zgt5.8

Neutral fraction

• From GP optical depth measurement, volume
  averaged neutral fraction increase by order of
  magnitude from z5.5 to 6.2

Fan et al. 2005
13
Gunn-Peterson Troughs

• Appearance of GP troughs show large line of sight
  variations
• J1148 (z6.42) detectable flux in ?, ?, ? IGM
  highly ionized
• J1030 (z6.28) and J1623 (z6.22) no flux in ?,
  ?, ?
• Upper limit on neutral fraction
• If IGM largely neutral, GP damping wing will wipe
  out all HII region transmissions
• Existence of transmission at zgt6 places an upper
  limit of average neutral fraction
• fHI lt 30

14
Evolution of HII region Size Around Quasars
zem

• Size of quasar HII region
• Rs (NQ tQ / xHI )1/3
• Size of proximity zone decreases by a factor of
  2.4 between z5.8 and 6.4
• Neutral fraction increased by a factor of 14
  over this narrow redshift range

Fan et al. 2005
15
No Evolution in Ly ? Galaxy LF at zgt6
Malhotra Rhoads

• Neutral IGM has extended GP damping wing --gt
  attenuates galaxy Ly ? emission line
• Lack of LF evolution --gt IGM neutral fraction lt
  30 - 50 (consistent with GP measurements)
• But systematics due to galaxy clustering and
  radiative transfer

16
Probing the first metals?

• GP effect saturates at zgt6
• Metal absorption line detected at zgt6
• Using metal lines to probe reionization?

White et al. 2003
Pettini et al. 2002
17
Metal Absorption Line Probe OI 1302

• Oh (2002)
• Use OI 1302 line
• With almost identical ionization potential as HI,
  in charge transfer equilibrium
• Low abundance probing high neutral fraction
• Predict OI forest during reionization
• Becker et al. (2005)
• Detection of strong OI systems at zgt6
• No OI forest
• But most systems come from J1148, the most
  transparent line of sight
• Consistent with high ionization at z6
• Uncertainties in IGM enrichment history.

Becker et al. 2005
18
Other probe GRB
Damping wing?
GRB050904

• Detected to z6.30
• Advantages
• Bright
• Flat K-correction due to time dilation at high-z
• No proximity effect, 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 lt 0.6 (2-sigma) by fitting both
  DLA and IGM profiles

Kawai et al. 2005
19
Summary of IGM Measurements

• IGM evolution accelerated at zgt6
• Neutral fraction increased by order of mag from
  z5.5 to zgt6
• fHI a few percent
• IGM temperature evolution
• IGM evolution is not uniform
• order of mag fluctuation in large scale UV
  background
• IGM is not mostly neutral at z6
• Transmission spikes in GP trough
• Lack of evolution in Ly? galaxy LF
• z6 marks the end of overlapping stage of an
  inhomogeneous reionization

20
WMAP early reionization

• Thompson scattering of CMB photons by free
  electrons during/after reionization
• --gt polarization and large scale TE correlation
• WMAP first year
• ? 0.17 /- 0.04
• Large signal comparing to late reionization model

Kogut et al. 2003
21
WMAP early reionization

• Inconsistent with a phase transition at z6
• Early reionization at z15 - 20
• However, no direct conflict to Gunn-Peterson
  result, which is sensitive only to 1 neutral
  IGM
• Overlapping could still be at z6
• IGM has complex reionization history
• ? Feedback from Galaxy Formation

zreion 6
Gnedin 2004
22
Reionization History with Feedback
all models normalized to ?e 0.17
H2-cooling
Photo-heating
Metal Enrichment
electron fraction
redshift
Haiman and Holder 2003
By introducing highly efficient star formation at
zgt10, and feedback effect to subsequent star
formation, models can fit both GP and
polarization results
23
What ionized the Universe AGNs, Star Formation
or Else
Density of quasars
SFR of galaxies
Bouwens et al.
Exponential decline of quasar density at
high redshift, different from normal galaxies

Richards et al. 2005, Fan e al. 2005
24
Reionization by AGNs?

• Can quasars do it?
• No too few quasars
• Can low-luminosity AGNs ionize the IGM by z6?
• Stacking X-ray image of LBGs in UDF too few
  faint AGNs
• Can accretion to seed BHs ionize the IGM by z15?
• Dijkstra, Haiman Loeb (2004)
• SXRB overproduced if quasars produce 10
  photons/H atom
• Preionization to f(HI)50 by X-rays is still
  allowed
• Constraint would tighten if SXRB better resolved

25
Reionization by stellar sources?
Necessary for reionization 6ltzlt9 (Stiavelli et al
2003)
Bunker et al 2004
Bouwens et al 2005

• Large uncertainties in reionization photon
  budget
• IGM clumpiness
• UV radiation and escape efficiency
• Large cosmic variance in deep field data
• Galaxy luminosity function at high-z

26
Summary

• When?
• Reionization started early (z15 - 20, WMAP)
• And ended late (z6, Gunn-Peterson)
• How?
• History likely complex
• Not a sharp phase transition in time
• feedback from galaxy formation
• Not homogeneous in space
• large scale structure
• What?
• Likely UV photons from star formation
• Hard photons from accretion could still
  pre-ionize to low-level at high-z

27
Whats Next?
WMAP
GRB, JWST 21cm, Planck