Probing the Cosmic Evolution with the Highest Redshift Quasars

1
Probing the Cosmic Evolutionwith the Highest
Redshift Quasars

• Xiaohui Fan
• Steward Observatory
• The University of Arizona

2
Introduction

• 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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Search for the HighestRedshift Quasars

• zgt4 600 known
• zgt5 30
• zgt6 6

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 trough
• Implication on the epoch of reionization
• Collaborators Strauss, Schneider, Becker,
  White, Richards, Penterricci, Rix, Narayanan 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 30,000 quasars discovered from SDSS
  data

Stellar locus
Z3
Z4
quasar
Z5

Fan, Richards, Newberg, Strauss
7

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SDSS Data Release 1

• Websitewww.sdss.org/dr1
• Photometry
• 2100 sq. deg
• 53 million objects in u,g,r,i,z
• 2.3TB data
• Limiting mag 22.2 in r, 20.5 in z
• Spectroscopy
• 1550 sq. deg
• 186,259 objects
• 134,000 galaxies
• 18,600 quasars
• R1800, 3800-9200 A, 30km/s redshift accuracy

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SDSS at Your Service Data Release 1
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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
• Rare objects ? contaminant elimination
• Elimination of false z-band only detections ?
  improved cosmic ray rejection
• 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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Highest-Redshift Quasars

• Aug 2003
• zgt4 600 (400 from the SDSS)
• zgt5 30 (25 from the SDSS)
• zgt6 6 from the SDSS (highest redshift at z6.42)
• SDSS i-dropout Survey
• By Spring 2003 4500 deg2 at zABlt20
• Eleven luminous quasars at zgt5.7
• 20 40 at z6 expected in the whole survey

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6.42

6.28
6.21
6.18

6.07
6.05
5.99
5.95
5.85
5.82
5.74
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The Lack of Evolution in Quasar Spectral
Properties

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Chemical Enrichment at zgtgt6?

• Strong NV emission ? consistent with supersolar
  metallicity
• Fe/alpha unchanged from low-z
• If Fe is mostly made out of Type Ia SN ? 1Gyr
  delay, not enough time?
• Fe production from Pop III???
• Question what exactly can we learn 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 if LF is similar
  to that at low-z ? first stars 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 most
  massive high-z galaxy
• 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
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• Submm and CO detection
• in the highest-redshift quasar
• Dust mass 108 109
• H2 mass 1010
• 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 ?
  possibly on-going star formation with rate of
  1000 solar mass/year

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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
transpartent and the dark ages ended
? today
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The end of dark ages Movie
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Neutral fraction
UV background
Gas density
Gas temperature
Gnedin 2000
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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, Fan, White et al.
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Keck/ESI 30min exposure ?
Gunn-Peterson Trough in z6.28 Quasar
Keck/ESI 10 hour exposure ?
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Strong Evolution ofGunn-Peterson Optical Depth
Transition at z6?
Fan et al. 2003
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Gunn-Peterson troughs confirmed by new zgt6 quasars
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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 1 neutral
• Marks the end of reionization epoch??

mass ave.
vol. ave
Fan et al. in prep
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Probing the first metals?
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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
• First massive stars as the source of earliest
  metal enrichment?
• Future observations
• Near IR spectroscopy metals at z6
• Absorption from different ions ? abundance and
  ionization state of the IGM
  

?
Pettini et al. 2003
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Reionization History Combining GP test with CMB

• G-P test shows at z6, the IGM is about 1
  neutral ? the tail end of the reionization
  process
• Discovery of three G-P troughs in the three
  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 seems to be more complicated by the
  simplest theory
• Reionization is not a phase transition
• Reionization last from 20 to 6? (600 million
  years) ?
• Whats Next?
• More quasars understanding the topology of the
  reionization from multiple lines of sights
• More sensitive to large neutral fraction GRBs?
  21cm?

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Did the Universe Reionize Twice?

• Challenge
• How can first star formation happen so early
• Why does reionzation epoch last so long?
• Cen (2002), Wyithe and Loeb (2003) propose twice
  reionization
• At z20 population III stars formed by H2
  reionized the universe
• IGM heats up and raises Jean mass ? star
  formation stops and HII recombines to form the
  second dark age
• z6 pop II forming with increasing global star
  formation rate resulting in the second
  reionization

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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 detections and possible X-ray weakness
• 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