The HighestRedshift Quasars: Probing the End of Cosmic Dark Ages

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The Highest-Redshift QuasarsProbing the End of
Cosmic Dark Ages

• Xiaohui Fan
• Steward Observatory
• The University of Arizona

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Quasars as Cosmology Probes

• The Study of Highest-Redshift Quasars Probes
• The epoch of first generation of galaxies/quasars
• Models of black hole formation
• Role of quasar/BH activity in galaxy evolution
• State of intergalactic medium
• Ionizing background at high-z
• History of reionization ? probing the end of
  cosmic dark ages
• Collaborators Strauss, Schneider, Becker,
  White, Richards, Penterricci, Rix, Narayanan,
  Hennawi, Carilli, Bertoldi, Walter, Cox, Lo et
  al. , SDSS Collaboration

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Exploring the Edge of the Universe
zgt7 galaxies

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SDSS at Your Service
Courtesy of Arizona graduate students
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The HighestRedshift Quasars Today

• zgt4 700 known
• zgt5 30
• zgt6 6
• Highest redshift
• z6.42

Total Discoveries
SDSS Discoveries
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17,000 Quasars from the SDSS Data Release One
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Ly a
3
2
CIV
redshift
CIII
1
MgII
OIII
Ha
0
wavelength
4000 A
9000 A
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z6 Quasars

• SDSS i-dropout Survey
• By early 2004 5000 deg2 at zABlt20
• Thirteen luminous quasars at zgt5.7
• By product gt 30 T dwarfs and large number of L
  dwarfs
• 20 40 at z6 expected in the whole survey

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Quasar Density at z6

• Based on nine zgt5.7 quasars
• Density declines by a factor of 20 from z3
• Cosmological implication
• MBH109-10 Msun
• Mhalo 1013 Msun
• How to form such massive galaxies and assemble
  such massive BHs in less than 1Gyr??
• The rarest and most biased systems at early times
• Using Eddington argument, the initial assembly of
  the system must start at zgtgt10
• ? co-formation and co-evolution of the earliest
  SBH and galaxies

Fan et al. in prep.
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Chemical Enrichment at zgtgt6

• Strong metal emission ? consistent with
  supersolar metallicity
• NV emission ? multiple generation of star
  formation
• Fe II emission ? might be from metal-free Pop III

Fan et al. 2004
Barth et al. 2003
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• Submm and CO detection
• in the highest-redshift quasar
• Dust mass 108 109Msun
• H2 mass 1010Msun
• Star forming rate 103/yr
• co-formation of SBH and
• young galaxies

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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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reionization
From Avi Loeb
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Neutral fraction
UV background
Gnedin 2000
Gas density
Gas temperature
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Increasing Lya absorption with redshift
zabs fobs/fcon -------------------------
-- 5.5 0.10 5.7
0.05 6.0 lt0.002 Zero flux over
300Å immediately blueward of Lya emission
in z6.28 quasar ? Detection of complete
Gunn-Peterson Trough tgtgt1 over large
region of IGM Becker et al. 2001

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Gunn-Peterson troughs confirmed by new zgt6 quasars
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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
• Measurement of the evolution of optical depth
• Probe the ionization state of the IGM
• Constrain the END of reionization

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Evolution of Ionizing Background

• Ionizing background estimated by comparing with
  cosmological simulations of Lyman absorption in a
  LCDM model
• Stronger constraint from the Lyß and Ly?
  Gunn-Peterson trough
• Ionizing background declines by a factor of gt25
  from z3 to z6
• Indication of a sudden change at z6?

Photoionizing rate
Fan et al. in prep
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Constraining the Reionization Epoch

• Neutral hydrogen fraction
• Volume-averaged HI fraction increased by gt100
  from z3 to z6
• Mass-averaged HI fraction gt 1
• Gunn-Peterson test only sensitive to small
  neutral fraction and saturates at large neutral
  fraction
• At z6
• Last remaining neutral regions are being ionized
• The universe is gt1 neutral
• Marks the end of reionization epoch??

mass ave.
vol. ave
Fan et al. in prep
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Comparing with Models
Mass-averaged
postoverlap
overlapping epoch
Pre- overlap
Volume-averageed
Fan et al. 2002
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The end of dark ages

• G-P test shows at z6, the IGM is about 1
  neutral ? the tail end of the reionization
  process
• Discovery of G-P troughs in the four highest
  redshift quasars known ? end of reionization at
  z6 with small dispersion among different lines
  of sight
• CMB polarization shows substantial ionization by
  z17
• Combining GP with CMB ? reionization history
• Reionization last from 20 to 6? (600 million
  years) ?
• Reionization is not a phase transition
• Reionization seems to be more complicated by the
  simplest theory

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Summary

• High-redshift quasars evolve strongly with
  redshift
• Density declines by 20 from z3 to z6
• Evolution much faster than normal galaxies
• High-redshift quasars are sites of spectacular
  star formation
• Sub-mm and CO detections ? high star formation
  rate
• Possible supersolar metallicity at zgt6 in quasar
  environment
• High-redshift quasars probe the end of
  reionization epoch
• Lya absorption increases dramatically at zgt5.7
• Consistent detections of complete Gunn-Peterson
  troughs in the highest-redshift objects
• At z6 ionizing background much lower, neutral
  fraction gt1, moderately overdense regions still
  neutral
• ? it marks the end of the reionization
  epoch when the last
  remaining HI in the IGM is being
  ionized
• ? combining with CMB results
  revealing the reionization history and the end of
  cosmic dark ages