Probing the End of Reionization with Highredshift Quasars

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Probing the End of Reionization
withHigh-redshift Quasars

• Xiaohui Fan
• University of Arizona
• Mar 18, 2005, Shanghai
• Collaborators Becker, Gunn, Lupton, Narayanan,
  Penterrici, Richards, Rix, Strauss, White et al.
• And SDSS collaboration

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Courtesy of Arizona graduate students
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The Highest Redshift Quasars Today

• zgt4 gt900 known
• zgt5 gt50
• zgt6 8
• SDSS i-dropout Survey
• By Fall 2004 6000 deg2 at zABlt20
• Sixteen luminous quasars at zgt5.7
• Many L and T brown dwarfs
• 30 at z6 expected in the whole survey

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Exploring the Edge of the Universe
New z7 galaxies

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High-redshift Quasars and the End of Cosmic Dark
Ages
Resolved CO emission from z6.42 quasar

• Existence of SBHs at the end of Cosmic Dark Ages
• BH accretion history in the Universe?

• Relation of BH growth and galaxy evolution?

• Probing the end of reionization?

Evolution of Quasar Density
Detection of Gunn-Peterson Trough
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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

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What Reionized the Universe?

• Based on SDSS quasar luminosity function
• Low-density relatively flat LF
• UV photons from luminous quasars and AGNs are not
  the major sources that ionized the universe

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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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Strong Evolution ofGunn-Peterson Optical Depth
Transition at z5.7?
Fan et al. 2004
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Implications of Complete Gunn-Peterson Trough

• G-P optical depth at z6
• Small neutral fraction needed for complete G-P
  trough
• By itself not indication that the object is
  beyond the reionization epoch
• The evolution of G-P optical depth
• Tracking the evolution of UV background and
  neutral fraction of the IGM
• Probe the ending of reionization

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Three stages
Pre-overlap
Overlap
Post-overlap
From Haiman Loeb
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Evolution of Ionizing Background

• Ionizing background estimated by comparing with
  cosmological simulations of Lyman absorption in a
  LCDM model
• Ionizing background declines by a factor of gt25
  from z3 to z6
• Indication of a rapid decline at zgt5.7
• Marks the tail end of reionization overlapping
  of individual HII regions at z6

Photoionizing rate
Fan et al. 2002, 2005
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Gunn-Peterson Troughs in theHighest-redshift
Quasars

• Four quasars known at zgt6.2
• Strong, deep Lya and Lyß absorption in all four
  objects immediately blueward of Lya emission
• None of the quasars at zlt6.2 shows any G-P
  troughs
• There is no Gunn-Peterson trough at zabslt5.8
• Transition happens at zgt5.8
• But LOS variation is significant

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Line of Sight Difference
Completely dark G-P trough
universe highly ionized in this line of sight!

White et al .2003
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Leaky IGM at z6

• Deep narrow band ACS imaging
• Lyß transmission point-like, coincides with
  quasar position
• ? IGM transmission at z6, not intervening
  galaxies, not lensed
• Gunn-Peterson Ly ? trough ?
• t lt 15, line of sight highly ionized (Oh
  Furlanetto 2004)

White, Becker, Fan and Strauss 2004
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Line of sight variations at the end of
overlapping?

• The last transmitting redshift ranges from 5.85
  to 6.15
• Non-uniform reionization?
• Expected if ionizing sources rare/clustered and
  HII bubbles have large sizes?

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Size of ionized bubbles at the end of reionization

• Wyithe and Loeb (2004)
• Completion of overlapping determined by the light
  crossing time of HII bubbles larger than the
  scattering of bubble formation time
• Scatter in the overlapping redshift of the order
  ?z 0.13, with a bubble size of 60 co-moving Mpc
  at z6
• Consistent with scatter seen in the last
  transmission redshift of z6 quasars

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Constraining the Reionization Epoch

• Neutral hydrogen fraction
• Volume-averaged HI fraction gt 0.1 at z6
• From G-P alone
• There is still a long way to go from tgt10 to
  t100,000
• Gunn-Peterson test only sensitive to small
  neutral fraction and saturates at large neutral
  fraction
• Need more sensitive tests to probe larger neutral
  fraction

mass ave.
vol. ave
Fan et al. in prep
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Size of Stromgren Sphere

• Size of HII region a function of quasar life-time
  and neutral fraction of the IGM
• Assume 107 yr lifetime ? n(HI) higher than 10 at
  least for some line of sight
• Calculation dependent on lifetime as well as
  detailed radiative transfer

• Sharp transition at the end of quasar proximity
  zone implies the boundary of HII region around
  quasar

Wyithe and Loeb, Mesinger and Haiman
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Put the picture together

• G-P results overlapping might be happening at
  z6 or slightly earlier
• CMB polarization shows substantial ionization by
  z17
• These two measurements are not contradictory
  combining GP with CMB ? complex reionization
  history
• First star formation happens very early?
• Reionization last from 20 to 6? (600 million
  years)
• Reionization is not a phase transition
• Multiple episodes of reionization?

?
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Probing the Reionization Epochbefore JWST

• More lines of sight from high-redshift quasars
• About 20 40 quasars 6 lt z lt 6.6 from SDSS
• Spectroscopy in far-optical and near-IR with
  large telescopes
• G-P test probing non-uniformity of the end of
  reionization
• Metal absorption lines at zgt6

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Probing the first Metals in the IGM?
10 hour Keck/ESI
J11485251

• 5 10 hour exposure in the far-optical and
  
• near-IR of z6 quasars on 6 10m class telescope
  
• High S/N to detect intergalactic CIV and SiIV
  absorption
• To probe the metal density of the IGM at zgt5
  

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Evolution of IGM CIV density

• No redshift evolution of CIV density from z2 to
  5
• IGM enriched in metal at zgtgt5
• Future observations
• Near IR spectroscopy metals at z6
• How does the IGM enrichment history trace the
  reionization history?
• Provide more sensitive probe to the neutral
  fraction?

?
Pettini et al. 2003
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Probing the Reionization Epochbefore JWST

• More lines of sight from high-redshift quasars
• About 20 40 quasars 6 lt z lt 6.6 from SDSS
• Spectroscopy in far-optical and near-IR with
  large telescopes
• G-P test probing non-uniformity of the end of
  reionization
• Metal absorption lines at zgt6
• Looking for objects at zgt7 first sources of
  light
• z6.6 is the limit of optical survey ? IR
  searches, UKIDSS, VISTA etc.
• High-redshift GRBs SWIFT!!!
• 21cm mapping of reionization
• ? mapping the complete history of reionization
  and early galaxy formation