The Most Distant Quasars: Probing the End of Cosmic Dark Ages

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The Most Distant QuasarsProbing the End of
Cosmic Dark Ages

• Xiaohui Fan
• Steward Observatory
• The University of Arizona

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The SDSS Collaboration
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The Most Distant QuasarsProbing the End of
Cosmic Dark Ages

• Xiaohui Fan
• Steward Observatory
• The University of Arizona

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40 Years AgoFirst Quasar 3C 273 by Maarten
Schmidt
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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

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Exploring the Edge of the Universe

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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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Outline

• SDSS Quasar Survey
• Search for the First Quasars
• Co-formation of First Quasars and Galaxies
• Lyman Absorption of z6 quasars
• Discovery of complete Gunn-Peterson troughs
• Implication on the epoch of reionization
• Collaborators Strauss, Schneider, Becker,
  White, Richards, Penterricci, Rix, Narayanan,
  Hennawi, Carilli, Bertoldi, Walter, Cox, Lo et
  al.

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SDSS Overview

• Primary Telescope 2.5m wide-field (2.5 deg)
• Imaging Survey (wide-field 54 CCD imager)
• Main Survey 10000 deg2
• Five bands, 3000 10000 Å
• rlim 22.5, zlim 20.5
• Spectroscopic Survey
• 106 galaxies (rlt17.8)
• 105 quasars ( 0 lt z lt 6.5)
• Interesting stars, radio/x-ray sources etc.

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SDSS Quasar Survey

• Color selected, flux-limited sample of 100,000
  quasars over 10,000 deg²
• Fully automated pipeline selection up to z5.5
• z band (9000 Å) allows detection of quasars up to
  redshift of 6.5
• Progress 50,000 quasars discovered from SDSS
  data

Stellar locus
Z3
Z4
quasar
Z5

Richards, Fan, Newberg, Strauss, et al. 2002
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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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Search for the First Quasars
Fan, Narayanan, Lupton, Strauss et al.

• Color selection of i-drop out quasars
• At zgt5.5, Lya enters z-band ? quasars have only
  red i-z measurement
• faint objects z-band only detections
• Technical Challenges
• Rarest objects
• One z6 quasar every 500 deg2
• Needles in a haystack ?
• one among 10 million objects and 5 million
  cosmic rays
• Key contaminant elimination
• Reliability of faint z photometry ? follow-up
  high S/N z photometry
• Major contaminants are L and T type Brown Dwarfs
  ? additional IR photometry

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Search for the First Quasars
Fan, Narayanan, Lutpon, Strauss et al.

• Separating z6 quasars and BDs
• Follow-up IR photometry
• For quasar z-J 1
• For late-L to T
• z-J gt 2

Zgt5.7 quasar
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Find the most distant quasarsneedles in a
haystack
Hobby-Eberly 9.2m
APO 3.5m
Kitt Peak 4m
Calar Alto (Spain) 3.5m
Keck 10m

• SDSS database
• 100 million objects

MMT 6.5m
4. Detailed spectra (12 new quasars at z6)
2..Photometric pre-selection 500 objects
3. Photometric and spectroscopic Identification
(50 objects)
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z6 Quasars

• SDSS i-dropout Survey
• By Dec 2003 5000 deg2 at zABlt20
• Twelve 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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The Lack of Evolution in Quasar Intrinsic
Spectral Properties

Ly a
NV
OI
Ly a forest
SiIV
Fan et al. 2004
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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
  
• Question what can we learn about star formation
  and chemical enrichment from abundance analysis
  of these most extreme environment in the early
  universe?

Fan et al. 2001
Barth et al. 2003
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Quasar Density at z6

• Based on nine zgt5.7 quasars
• Density declines by a factor of 20 from z3
• Number density implies that quasars are unlikely
  to provide enough UV background ? earliest
  galaxes ionized the universe!
• 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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Sub-mm and Radio Observationof High-z Quasars

• Probing dust and star formation in the high-z
  quasar host galaxies
• Using IRAM and SCUBA 40 of radio-quite quasars
  at zgt4 detected at 1mm (observed frame) at 1mJy
  level
• Combination of cm and submm
• ? submm radiation in
• radio-quiet quasars
• come from thermal
• dust with mass 108 Msun
• If dust heating came from starburst
• ? star forming rate of
• 500 2000 Msun/year
• ?Quasars are likely sites
• of intensive star formation

Arp 220
Bertoldi 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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Co-evolution of early galaxies and supermassive
BHs

• Presence of 109-10 solar mass BH at zgt6 ?
  it has to begin the assemble at zgt10
• High metallicity in the quasar environment ?
  recent star formation and chemical enrichment
• Presence of heated dust (submm) and gas ?
  possible on-going star formation with rate of
  1000 solar mass/year
• ? The initial assembly of SBH coeval with the
  initial assemble of host galaxy
• Spitzer and ALMA ? Probing the BH/galaxy
  formation connection

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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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A brief cosmic history

• recombination

• Cosmic Dark Ages no light
• no star, no quasar IGM HI

• First light the first galaxies
• and quasars in the universe

• Epoch of reionization radiation from the first
  object lit up and ionize IGM HI ? HII

? reionization completed, the universe is
transparent and the dark ages ended
? today
Courtesy G. Djorgovski
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Neutral fraction
UV background
Gnedin 2000
Gas density
Gas temperature
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Neutral fraction
UV background
Gas density
Gas temperature
Gnedin 2000
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The end of dark ages Movie
Courtesy of N. Gnedin
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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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VLT/FOS2
Pentericci et al. 2002

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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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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
• For uniform IGM
• Measurement of optical depth can be used to
  constrain ionizing background
• IGM is highly non-uniform
• regions with different density have different
  Lya transmission
• to constrain ionization state have to take
  into account the density distributions of the IGM

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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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Whats next?

• More quasars understanding the topology of the
  reionization from multiple lines of sights
• Evolution of heave element chemical enrichment
  and feedback from the first galaxies
• Pushing towards higher redshifts IR surveys,
  JWST ? finding the first light
• More sensitive to large neutral fraction
• GRBs? 21cm?
• Detailed comparison with CMB polarization
• ? Mapping the reionization history and the end
  of the cosmic dark ages

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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