GunnPeterson Effect and The End of Reionization

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Gunn-Peterson Effect and The End of Reionization

• Xiaohui Fan
• University of Arizona

Collaborators Becker, Carilli, Hennawi, Jiang,
Richards, Schneider, Strauss, Walter, White, et
al. SDSS collaboration
Background 46,420 Quasars from the SDSS Data
Release Three
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reionization
From Avi Loeb
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Quest to the Highest Redshift Quasars
IR survey (UKIDSS, VISTA)
SDSS

APM CCD

Radio
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The Highest Redshift Quasars Today

• zgt4 gt1000 known
• zgt6 14
• SDSS i-dropout Survey
• Completed in June 2006
• 7700 deg2, zAB lt 20
• 25 luminous quasars at 5.7ltzlt6.4
• Other on-going z6 quasar surveys
• AGES (Cool et al.) Spitzer selected, one quasar
  at z5.8
• FIRST-Bootes (Becker et al.) radio selected, one
  quasar at z6.1
• QUEST, CFHT i-dropout surveys similar to SDSS
• Future IR-based survey UKIDSS, VISTA, allows
  detection up to z8-9.

• SDSS2 faint quasars in the deep SDSS stripe
  (Jiang, XF et al.), 10 - 30 additional z6
  quasars in next three years (four z6 quasar in
  pilot obs)

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Keck/ESI 30min exposure ?
Gunn-Peterson Trough in z6.28 Quasar
Keck/ESI 10 hour exposure ?
White et al. 2003
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Three stages
Pre-overlap
Overlap
Post-overlap
From Haiman Loeb
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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

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History of ReionizationOpen Questions

• Whats the Status of IGM at z6?
• Measurements of Gunn-Peterson optical depth
• Evolution of UV background
• Constraints on IGM neutral fraction
• Was the Universe mostly neutral by z6-8?
• Distribution of dark gaps
• Evolution of Lyman alpha emitters
• What is the source of reionization?
• How to probe the neutral epoch?
• Sources at higher redshift
• New tests on neutral fraction

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Evolution of Lyman Absorptions at z5-6
?z 0.15
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Evolution of Gunn-Peterson Optical Depth
(1z)4.5
XF et al. 2006
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Accelerated Evolution at zgt5.7

• Optical depth evolution accelerated
• zlt5.7 ? (1z)4.5
• zgt5.7 ? (1z)gt11
• End of reionization?
• 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
XF et al. 2006
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Evolution of Ionization State
UV background

• UV Ionizing background
• Assuming photoionization and model of IGM density
  distribution
• 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 gt order of
  magnitude from z5.5 to 6.2

XF et al. 2006
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Relation between optical depth and neutral
fraction highly model-dependent

• Becker et al. (2006)
• optical depth evolution could be consistent with
  a smooth evolution of ionizing background for a
  log-normal density distribution of the IGM

• Relation between ? and ? dependent on IGM
  clumpiness
• Simulation results clumpiness 5 - 30, no
  strong evolution at z6
• Optical depth evolution driven by an decreasing
  background towards high-z

Becker et al. 2006
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Dark Gap Distributions

• Dark gap statistics (Songaila Cowie 2002)
• Gaps regions where all pixels have ?gt2.5
• Gaps among z6 quasars
• Average length shows the most dramatic increase
  at zgt5.8 ? IGM is dominated by long, dark gaps
• Consistent with overlap at z6-8?
• Dispersions
• Even at zgt6, gap lengths are still finite
• 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 lt30
• Independent upper limit on neutral fraction

XF et al. 2006
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Dark Gap Statistics Comparison with Simulations

• Gallerani et al. (2006)
• Early reionization (zoverlap 15)
• Late reionization (zoverlap 7)
• Significant difference in gap distribution at z6
• Allows neutral fraction constraints where G-P
  saturates

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Evolution of Proximity Zone Size Around Quasars
Haiman, Mesinger, Wyithe, Loeb et al.

• Size of Proximity Zone region
• Rp (NQ tQ / fHI )1/3
• Size of quasar proximity zone decreases by a
  factor of 2.4 between z5.8 and 6.4 (Fan et al.
  2006)
• Consistent with neutral fraction increased by a
  factor of 15 over this narrow redshift range
• Actual size of proximity zone dependent on
  details of radiative transfer and quasar model

Proximity zone size (Mpc)
XF et al. 2006
redshift
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Uncertainties in interpretation of proximity zone
sizes

• Bolton Haehnelt (2006), Maselli et al. (2006)
• Observed size of proximity zone much smaller than
  true HII region size
• Neutral fraction lt a few percent
• Consistent with G-P constraints
• Mesinger et al. (2004), Wyithe et al. (2005)
• Neutral fraction 10-30
• Better models and simulated spectra needed

Maselli et al. 2006
Bolton Haehelt 2006
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Ly ? Galaxy LF at zgt6
Iye et al. 2006 Kashikawa et al. 2006

• Neutral IGM has extended GP damping wing ?
  attenuates Ly ? emission line
• New Subaru results
• Declining density at z6-7 (2-3? result)
• Reionization not completed by z6.5
• Neutral fraction could be as high as a few tenths
  but strongly model-dependent
• cf. Malhotra Rhoads, Hu et al. lack of
  evolution in Ly ? galaxy density

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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
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Reionization by AGNs?
XF et al. 2003

• 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)
• Soft X-ray background overproduced if quasars
  produce 10 photons/H atom
• Preionization to f(HI)50 by X-rays is still
  allowed

Observerd UV background
Contributions from AGN
Hopkins et al. 2006
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Reionization by stellar sources?
Necessary for reionization 6ltzlt9 (Stiavelli et al
2003)

• 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

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Probing Reionization History

WMAP
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Probing Neutral Era

• 21cm probes
• HI emission during reionization
• 21cm Gunn-Peterson effects in high-z radio
  sources
• Metal absorption lines (Oh 2002, Becker et al.
  2005)
• Ly? galaxy distributions (e.g. Malhotra and
  Rhoads) G-P gap distribution
• GRBs

Gnedin Shiver McQuinn et al. Carilli et al.
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GRBs as Probes of Reionization
Damping wing?
GRB050904

• Detected to z6.30
• Advantages
• Bright
• Flat K-correction due to time dilation at high-z
• 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 lt 0.6 (2-sigma) by fitting both
  DLA and IGM profiles

Kawai et al. 2005
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Summary

• IGM evolution accelerated at zgt6
• Neutral fraction increased by order of mag from
  z5.5 to zgt6
• fHI a few percent, but highly model-dependent
• 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
• Density evolution of Ly? galaxies
• z6 marks the end of overlapping stage of an
  inhomogeneous reionization