Observation Constraints of the End of Reionization

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Observation Constraints of the End of
Reionization

• Xiaohui Fan
• University of Arizona

Collaborators Becker, Carilli, Ferrara,
Gallerani, Jiang, Richards, Roy Choudhury,
Strauss, Xu, Walter, White, et al.
Background 46,420 Quasars from the SDSS Data
Release Three
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The Highest Redshift Quasars Today

• z4 1000 known
• z6 19
• SDSS i-dropout Survey
• Completed in June 2006
• 7700 deg2, zAB
• 27 luminous quasars at 5.71
• CFHT High-z Quasar Survey (CFHTQS, Willott et al.
  astro-ph/0706091)
• Goal 400 deg2, zAB
• 4 quasars at z6
• New highest-z quasar at z6.43
• SDSS Faint Quasar Survey (SFQS)
• faint quasars in the deep SDSS stripe (Jiang, XF
  et al.),
• 300 deg2, zAB
• six z6 quasar at 20
• Goal quasar LF

• 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 i-dropout surveys similar to SDSS
• IR-based survey UKIDSS, (z5.83), VISTA, allows
  detection up to z8-9.

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Quasar Density at z6

• From SDSS i-dropout survey
• Density declines by a factor of 40 from between
  z2.5 and z6
• Cosmological implication
• MBH109-10 Msun
• Mhalo 1012-13 Msun
• rare, 5-6 sigma peaks at z6 (density of 1 per
  Gpc3)
• Assembly of supermassive BHs?
• The universe is only 20 teddington old,
  requiring non-stop Eddington accretion of 100
  Msun from z20
• Is Eddington-limited accrection from stellar
  seeds still permitted, or are alternative
  accretion modes (super-Eddington, intermediate
  mass BH) needed?

Fan et al. 2006
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The Lack of Evolution in Quasar Emission Line
Properties

z6 composite
Ly a
Low-z composite
NV
OI
SiIV
Ly a forest
Fan et al.2007

• Rapid chemical enrichment in quasar vicinity
• Quasar env has supersolar metallicity no
  metallicity evolution
• High-z quasars are old, not yet first quasars..

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Quasar Metallicity at z6
near-IR spectroscopy Gemini Keck
Jiang, XF et al. 2007
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reionization

• Two Key Constraints
• WMAP 3-yr zreion10/-3
• 2. IGM transmission zreion 6

From Avi Loeb
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End of Reionization EpochOpen 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
• HII region size distribution
• Evolution of Lyman alpha emitters
• What is the source of reionization?
• First galaxies or AGNs

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Searching for Gunn-Peterson Trough

• Gunn and Peterson (1965)
• It is observed that the continuum of the source
  continues to the blue of Ly-a ( in quasar 3C9,
  z2.01)
• only about one part of 5x106 of the total mass
  at that time could have been in the form of
  intergalactic neutral hydrogen
• Absence of G-P trough ? the universe is still
  highly ionized at z6

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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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Evolution of Lyman Absorptions at z5-6
?z 0.15
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Accelerated Evolution at z5.7

• Optical depth evolution accelerated
• z
• z5.7 ? (1z)11
• 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 z6
• 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 z5.8

Neutral fraction

• From GP optical depth measurement, volume
  averaged neutral fraction increase by 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
  strongly-evolving 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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Evolution of Proximity Zone Size Around Quasars
Shapiro, Haiman, Mesinger, Wyithe, Loeb et al.

• Size of Proximity Zone region
• Rp (LQ 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
• Can be applied to higher z and fHI with lower S/N
  data
• 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
• 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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CFHTQS results (Willott et al. 2007)

• Strong evolution in ?GP seen at z5.5, but low
  S/N
• Scaled near-zone size 6-11 Mpc at z6
• Consistent with a low fHI
• But uncertainties in zem based on Ly?
• Caution using Ly? redshift could introduce large
  uncertainty in HII region size but true
  systematic redshift difficult for faint quasars
  at z6

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Dark Gap Distributions

• Dark gap statistics (Songaila Cowie 2002)
• Gaps regions where all pixels have ?2.5
• Gaps among z6 quasars
• Average length shows the most dramatic increase
  at z5.8 ? IGM is dominated by long, dark gaps
• Consistent with overlap at z6-8?
• Dispersions
• Even at z6, 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 z6 places an upper
  limit of average neutral fraction
  et al. 2007)
• Independent upper limit on neutral fraction

XF et al. 2006
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Dark Gap Statistics Comparison with Simulations

• Gallerani et al. (2006, 2007)
• Early reionization (zoverlap 15)
• Late reionization (zoverlap 7)
• Significant difference in gap distribution at z6
• fHI
• But observed transmission peaks too wide compared
  to simulations

Distribution of width of transmission peaks
Distribution of dark gaps
5.7
6.0
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Ly ? Galaxy LF at z6
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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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 DLA and IGM profiles

Kawai et al. 2005
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What Ionized the Universe? AGNs or Galaxies
Density of quasars
SFR of galaxies

• Quasar LF at z6
• SDSS Wide 7700 deg2, 17 quasars, zAB
• SDSS Deep 150 deg2, 6 quasars, 20
• AGES 1 quasar in 5 deg2 at zAB
• Steeppening of LF
• ??L-3.1
• Comparing to ??L-2.4 at z4

Jiang, XF et al. 2007
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Reionization by AGNs?

• Can quasars do it?
• Too few quasars unless QLF remains to be steep to
  AGN luminosity
• 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 (e.g. Ricotti et al.)

Jiang, XF et al. 2007
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Summary

• IGM evolution accelerated at z6
• Neutral fraction increased by order of mag from
  z5.5 to z6
• fHI a few percent, but highly model-dependent
• z6 marks the end of overlapping stage of an
  inhomogeneous reionization
• z6 quasars are old lots of BH build-up and
  chemical enrichment at high-z
• AGN not likely sources of reionization

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Probing Reionization History

WMAP
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Surveys of quasars at z7
LBT LBC-Red i-z-Y selection (1 deg2/night)
UKIDSS YJHK photometry